PUBLIC  WATER-SUPPLIES 

REQUIREMENTS,  RESOURCES,  AND 

THE   CONSTRUCTION 

OF  WORKS 


BY 
F.  E.  TURNEAURE,  DR.  ENG.,  AND  H.  L.  RUSSELL,  PH.D. 

Dean  of  the  College  of  Engineering  Dean  of  the  College  of  Agriculture 

UNIVERSITY  OP  WISCONSIN 


WITH  A  CHAPTER 


Professor  of  Hydra 


SECOND  EDITION.     REVISED  AND  ENLARGED 
TOTAL    ISSUE,    SEVENTEEN    THOUSAND 


NEW  YORK 

JOHN  WILEY  &  SONS,  INC. 

LONDON:   CHAPMAN   &  HALL,  LIMITED 

1916 


COPYRIGHT,  1901,  1908, 

BY 
F.  E.  TURNEAURE  AND  H.  L.  RUSSELL 


CAT.  FOR 
PUBLIC  HEALTH 

Stanhope  ipreas 

f.  H.  GILS  ON     COMPANY 
BOSTON.    U.S.A. 


PUBLIC 
HEALTH 
LIBRARY 


PREFACE  TO   THE   SECOND   EDITION. 


SINCE  the  publication  of  the  first  edition  of  this  work,  in  1901,  there  has 
been  a  noteworthy  development  in  the  design  and  construction  of  works, 
for  public  water-supplies.  While  this  development  has  been  greatest  in 
the  methods  of  water  purification  and  in  the  construction  of  purification 
works  for  the  large  cities  of  the  country,  yet  it  may  be  said  that  the  engi- 
neering of  water-works  has  in  general  been  brought  to  a  more  scientific  as 
well  as  economical  basis.  In  the  revision  of  this  work  the  authors  have 
endeavored  to  bring  it  into  accordance  with  the  best  modern  practice. 

The  chapters  relating  to  the  purification  of  water  have  been  thoroughly 
revised,  that  on  mechanical  or  rapid  filtration  being  rewritten  and  greatly 
enlarged.  In  view  of  the  essential  differences  between  the  two  systems  of 
filtration  and  the  direction  along  which  their  development  is  taking  place 
the  authors  decided  to  change  the  term  "mechanical  filtration,"  formerly 
used,  to  "  rapid  sand  filtration,"  and  to  employ  the  term  "  slow  sand 
filtration"  for  the  other  system.  The  subject  of  coagulation  is  now  made 
an  important  part  of  the  chapter  on  Sedimentation  and  Coagulation. 
Besides  the  matter  relating  to  purification  many  other  changes  and 
additions  have  been  made  in  nearly  every  chapter.  The  most  important 
of  these  relate  to  methods  of  bacterial  examination  of  water,  the  investi- 
gation of  ground-water  and  the  construction  of  collecting  works,  data  on 
the  use  of  water,  data  on  rainfall  and  flow  of  streams,  the  construction  of 
dams,  and  the  application  of  reinforced  concrete  to  conduits,  dams, 
filters,  reservoirs,  and  tanks.  The  literature  of  each  chapter  has  also 
been  extended  and  brought  up  to  date. 

F.  E.  T. 
H.  L.  R. 

MADISON,  Wis.,  July,  1908. 


380 


PREFACE   TO   THE   FIRST   EDITION. 


THE  present  volume  has  been  prepared  with  particular  reference  to 
the  needs  of  teachers  and  students  in  technical  schools  in  which  the 
subject  of  Water-supply  receives  a  considerable  amount  of  attention. 
The  work  is  based  chiefly  upon  the  experience  of  the  first-named 
author  in  teaching  the  subject  for  a  number  of  years  in  the  institution 
with  which  he  is  connected,  and  has  been  written  with  special  reference 
to  use  in  his  own  class-room. 

In  the  discussion  of  the  various  subjects  treated,  the  endeavor  has 
been  to  lay  stress  upon  fundamental  principles  rather  than  upon  details 
of  practice,  although  methods  of  construction  have  been  freely  given 
where  they  might  serve  to  illustrate  the  principles  involved  or  bring  out 
the  effects  of  differences  in  conditions.  With  the  same  idea  in  mind 
many  problems,  usually  treated  empirically,  have  been  subjected  to 
analysis,  more  or  less  crude,  but  useful  for  calling  attention  to  certain 
general  laws  and  limitations.  It  is  believed  also  that  such  analyses  may 
often  be  of  much  assistance  in  utilizing  the  results  of  observation,  and 
that,  if  properly  applied,  they  will  aid  much  in  the  cultivation  of  the 
judgment.  The  necessity  for  the  designer  to  keep  constantly  before 
him  the  question  of  true  economy  has  been  frequently  emphasized,  and 
to  aid  the  beginner  a  brief  general  discussion  of  this  subject  has  been 
given  in  Chapter  XI.  No  apology  is  necessary  at  this  time  "for  the  com- 
paratively full  treatment  given  to  the  subject  of  the  Quality  of  Water- 
supplies  in  Chapters  VIII,  IX,  and  X.  The  authors  have  felt  that  the 
great  importance  of  questions  relating  to  the  purification  of  water  requires 
a  more  thorough  presentation  of  the  sanitary  phase  of  the  subject  than 
has  heretofore  been  customary  in  works  designed  for  engineers.  The  sub- 
ject of  Ground-water  has  also  received  considerably  more  attention  than 
is  usual,  but,  it  is  thought,  not  more  than  the  importance  of  the  subject 
will  justify. 

References  to  authorities  are  numerous,  and  the  plan  has  been  adopted 
of  giving,  at  the  end  of  each  chapter,  a  brief  list  of  the  best  literature  of 
the  subject  treated.  It  is  believed  that  this  feature  will  prove  of  value 
not  only  to  the  student,  but  especially  to  the  young  practitioner  who 
finds  it  necessary  to  make  a  special  study  of  a  particular  branch  of  the 


VI  PREFACE  TO  THE  FIRST  EDITION. 

subject.  According  to  the  authors'  view,  there  is  no  branch  of  the  pro- 
fession in  which  a  good  working  library,  consisting  largely  of  periodicals, 
is  more  necessary  than  in  that  of  municipal  or  sanitary  engineering. 

To  the  water-works  specialist  there  is  doubtless  little  that  is  new  to  be 
found  in  this  work,  but  it  is  hoped  that  the  form  in  which  a  large  amount 
of  widely  scattered  information  has  here  been  presented  will  prove  of  con- 
venience to  this  class  of  readers. 

With  regard  to  the  authorship  it  is  proper  to  say  that  Chapters  VIII, 
IX,  and  X  are  by  Prof.  Russell;  also  several  of  the  articles  of  Chapters 
XIX  to  XXIII,  which  relate  more  specifically  to  bacteriological  and 
chemical  features.  The  remainder  of  the  work,  with  the  exception  of  the 
chapter  on  Pumping-machinery,  has  been  written  by  Prof.  Turneaure. 

The  authors  desire  to  acknowledge  their  indebtedness  to  the  various 
engineers  and  water-works  officials  who  have  kindly  responded  to 
requests  for  information.  They  are  also  under  special  obligations  to 
Mr.  C.  B.  Stewart,  Assoc.  M.  Am.  Soc.  C.  E.,  for  a  very  thorough 
investigation  of  the  literature  of  the  flow  of  water  in  pipes,  the  results 
of  which  appear  on  pages  227-234,  including  the  diagram  of  Fig.  34. 
Of  the  large  number  of  original  articles  and  papers  which  have  been 
consulted,  a  great  many  have  appeared  in  the  Engineering  News,  the 
Engineering  Record,  or  the  Transactions  of  the  American  Society  of  Civil 
Engineers;  and  to  the  publishers  of  these  journals  special  thanks  are  due 
for  many  of  the  illustrations  which  appear  in  this  work. 

F.  E.  T. 

H.  L.  R. 

MADISON,  Wis.,  March,  1901 


CONTENTS. 


CHAPTER   I. 

INTRODUCTION. 

PAGE 

HISTORICAL  SKETCH.  —  Water-supplies  in  Ancient  Times  —  Water-works  of  the  Romans 
-  The  Middle  Ages  —  Development  of  Modern  Water-works  in  Europe  —  Devel- 
opment of  Water-works  in  the  United  States i 

VALUE  AND  IMPORTANCE  OF  A  PUBLIC  WATER-SUPPLY.  —  Domestic  Use  —  Commercial 

Uses  —  Public  Uses  —  Literature .  .  12 


PART    I. 

REQUIREMENTS    AND    RESOURCES. 
A.     QUANTITY  OF  WATER  REQUIRED:   SOURCES  OF  SUPPLY. 

CHAPTER  II. 

QUANTITY  OF  WATER  REQUIRED. 

Nature  of  the  Problem  —  Consumption,  How  Stated  —  Influences  Affecting  the  Con- 
sumption per  capita  —  Consumption  of  Water  for  Various  Purposes  —  Total 
Consumption  per  capita  —  Increase  in  Consumption  —  Variations  in  Consumption 
—  Consumption  in  European  Cities  —  Growth  of  Cities  —  Literature 15 

CHAPTER   III. 

SOURCES  OF  SUPPLY. 

Classification  —  Quality  of  Water  from  Various  Sources  —  Utilization  of  the  Various 

Sources 38 

CHAPTER    IV. 

THE  RAINFALL. 

Measurement  of  Rainfall  —  Rainfall  Statistics  —  Mean  Annual  Rainfall  —  Secular 
Variations  in  the  Rainfall  —  Mean  Monthly  Rainfall  —  Minimum  Yearly  Rainfall  — 
Maximum  Rates  of  Rainfall  —  Extent  of  Great  Rain-storms  — -  Literature 41 

CHAPTER    V. 

EVAPORATION  AND  PERCOLATION. 

Relation  of  Evaporation  and  Percolation  to  Stream -flow  and  to  Ground-water. 54 

EVAPORATION  FROM  WATER-SURFACES.  —  Influences  Affecting  Evaporation  —  Experi- 
ments on  Evaporation  from  Water-surfaces  —  Calculated  Evaporations  from  Water- 
surfaces 55 

vii 


Vlll  CONTENTS. 

PAGE 

PERCOLATION  AND  EVAPORATION  FROM  LAND-SURFACES.  —  Influences  Affecting  Evapora- 
tion and  Percolation  —  Effect  of  Vegetation  or  Other  Soil -covering  —  Experiments 
on  Evaporation  and  Percolation  —  Evaporation  as  Determined  from  Stream-flow  — 
Amount  of  Percolation  over  Large  Areas  —  Literature 57 

CHAPTER   VI. 

FLOW  OF   STREAMS. 

General  Methods  of  Procedure  —  Influences  Affecting  Stream-flow  —  Units  of  Measure 

—  Division  of  the  Subject 66 

MINIMUM  FLOW 68 

MAXIMUM  OR  FLOOD  FLOW.  —  General  Considerations  —  Data  of  Maximum  Rates  of 
Flow  —  Formulas  for  Flood-flow  —  Rational  Method  of  Estimating  Flood-flow  — 
Diagram  of  Flood-flows  —  Example  —  Some  Great  Floods 69 

TOTAL  FLOW  FOR  VARIOUS  PERIODS  OF  TIME.  —  Statistics  of  Stream-flow  —  Minimum 
Yearly  Flow  —  Monthly  and  Seasonal  Flow  —  Estimates  of  Flow  —  Effect  of  Lakes 
and  Ponds  on  Stream-flow  —  Example  of  Estimate  of  Flow  —  Literature 78 

CHAPTER    VII. 

GROUND-WATER. 

GENERAL  CONSIDERATIONS.  —  Occurrence  of  Ground-water  —  General  Form  of  the 
Water-table  —  Porosity  of  Soils  —  Formations  Favorable  for  the  Transmission  of 
Ground-water  —  Occurrence  of  Water-bearing  Formations 89 

FLOW  OF  GROUND-WATER.  —  Methods  of  Determining  the  Flow  of  Ground-water  — 
Formula  for  Estimating  Velocity  of  Flow  —  Direct  Method  of  Determining  Velocity 
—  Quantity  Flowing  —  Quantity  Available 94 

SPRINGS.  —  Formations  of  Springs  —  Yield  of  Springs 102 

ARTESIAN  WATER.  —  General  Conditions  —  Use  of  the  Word  "  Artesian  "  —  The  Char- 
acter and  Inclination  of  the  Strata  —  Capacity  —  Predictions  Concerning  Artesian 
Wells  —  Important  Artesian  Areas  in  the  United  States  —  Literature 106 


B.    QUALITY  OF   WATER-SUPPLIES. 

CHAPTER    VIII. 

EXAMINATION  OF  WATER-SUPPLIES. 

Scope  and  Extent  of  Examination  —  Necessity  of  Full  Data  in  Interpreting  Conditions  — 
Collection  of  Samples  —  Sanitary  Analysis  of  Water  —  Detection  of  Pollution  by 
Addition  of  Chemicals  —  Various  Analytical  Methods  —  Value  of  Different  Methods.  1 1 5 

PHYSICAL  EXAMINATION  OF  WATER.  —  Color  —  Turbidity  —  Odor  and  Taste  —  Tem- 
perature —  Chemical  Reaction 122 

CHEMICAL  EXAMINATION  OF  WATER.  —  Purpose  of  Chemical  Tests  —  Expression  of 
Chemical  Data  —  Interpretation  of  Chemical  Data  —  Total  Solids  and  Character 
of  Same  —  Loss  on  Ignition  —  Chlorine  —  Organic  Matter  —  Free  and  Albuminoid 
Ammonia  —  Oxygen  Consumption  —  Nitrites  —  Nitrates  —  Summary. 125 

BACTERIAL  EXAMINATION  OF  WATER.  —  Development  of  Methods  —  Scope  of  Bacterial 
Tests  —  Methods  of  Determining  Bacteria  —  Multiplication  of  Bacteria  in  Col- 
lected Sample  —  Quantitative  Bacterial  Analysis  —  Qualitative  Bacterial  Analysis  — 
Presumptive  Tests  —  Litmus-Lactose  Agar  Test  —  Fermentation  Tests  —  Number 


CONTENTS.  ix 

PAGE 

of  Species  —  Significance  of  Liquefying  Bacteria  —  Significance  of  Colon  Bacillus  — 
Other  Sewage  Types  —  Isolation  of  Sewage  Types  —  Animal  Tests  —  Concentra- 
tion of  Organisms  in  Water — Detection  of  Specific  Disease-bacteria  —  Isolation 
of  Typhoid  Organism  —  Isolation  of  Cholera  —  Disinfection  of  Polluted  Wells  and 
Pipes  —  Bacterial  Control  of  Filter  Operations 131 

MICROSCOPICAL  EXAMINATION  OF  WATER.  —  Scope  of  Microscopic  Examinations  — 

Direct  Microscopic  Examination  in  Filtration-work 143 

SANITARY  SURVEYS.  —  Object  and  Value  —  Literature 144 

CHAPTER  IX. 

QUALITY  O?  WATER. 

Importance  of  Quality  —  Changes  in  Quality  Determined  by  Course  of  Water  —  Require- 
ments as  to  Quality  —  Potableness  —  Water  for  Domestic  Use  —  Water  for  Manu- 
facturing Purposes  —  Distribution  of  Bacteria  in  Soil 149 

METEORIC  WATERS. —  Absorption  of  Impurities  from  Air. 153 

SURFACE-WATERS.  —  Character  Determined  by  Nature  of  Underlying  Soil  —  Surface- 
waters  as  Potable  Supplies  —  Physical  Appearance  —  Bacterial  Condition  of  Flow- 
ing Streams  —  Self-purification  of  Streams  —  Causes  of  Self-purification  of  Streams 

—  Dilution  —  Sedimentation  —  Vital     Concurrence  —  Unsuitable     Food-supply  — 
Aeration  —  Chemical   Reaction  —  Conclusion  —  Vertical   Circulation  in  Lakes  — 
Bacterial  Content  of  Open  Surface-waters  —  Natural  Purification  Processes  —  Influ- 
ence of  Vegetation  —  Odors  in  Water-supplies  —  Influence  of  Freezing  on  Bacterial 
Life 154 

SUBTERRANEAN  WATERS.  —  Change  in  Quality  Due  to  Percolation  —  Purification  of 
Water  in  the  Soil  —  Capacity  of  Soil  for  Purification  —  Extent  of  Filtration  Necessary 
to  Effect  Purification  —  Spring-waters  —  Well-waters  —  Bacterial  Content  of  Wells 

—  Effect  of  Pumping  —  Effect  of  Organic  Nutriment  on  Growth  of  Water-bacteria 

—  Artesian  Wells 169 

EFFECT  OF  STORAGE  AND  DISTRIBUTION  ON  QUALITY.  —  Improvement  of  Water  by 

Storage  —  Impairment  of  Water  by  Storage  —  Effect  of  Distribution  on  Quality — 
Literature 177 

CHAPTER    X. 

COMMUNICABLE  DISEASES  AND  WATER-SUPPLIES. 

Relation  of  Water-supplies  to  Disease  Dissemination  —  The  Germ-theory  of  Disease  — 

Specific  Nature  of  Water-borne  Disease-germs  —  Diseases  Due  to  Parasitic  Worms.  181 

INFECTIOUS  DISEASES  TRANSMISSIBLE  BY  WATER-SUPPLIES.  —  Conditions  Necessary  for 
Infection  —  Water-borne  Diseases  Affect  Intestinal  Canal  —  The  Most  Important 
Water-borne  Diseases  —  Typhoid  Fever  —  Typhoid  Fever  and  Sewage  Pollution  — 
Mohawk  Valley  Epidemic  —  Lowell-Lawrence  Epidemic  —  Pollution  of  Lake-towns 

—  Typhoid  and  Polluted  Wells  —  Outbreaks  Inaugurated  from   Single  Cases  — 
Typhoid  Rates  an  Index  of  Quality  of  Water  —  Diminished  Typhoid  Rates  Incident 
to  Improved  Supplies  —  Seasonal  Distribution  of  Typhoid  Fever  —  Asiatic  Cholera 

—  Cholera  Outbreaks  traced  to  Water-supplies  —  Anthrax  —  Other  Water-borne 
Diseases  —  Gastro-intestinal  Disturbances  —  Dysentery  —  Malaria 183 

VITALITY  OF  PATHOGENIC  BACTERIA  IN  WATER.  —  Conditions   Affecting  Vitality  — 

Vitality  of  Typhoid  Organism  —  Cholera  —  Anthrax  — Literature 199 


X  CONTENTS. 

PART    II. 
THE   CONSTRUCTION   OF   WATER-WORKS. 

CHAPTER   XL 

GENERALITIES  PERTAINING  TO  WATER-WORKS  CONSTRUCTION. 

GENERAL  ARRANGEMENT  OF  WATER-WORKS.  —  Classification  —  Works  for  the  Collec- 
tion of  Water  —  Works  for  the  Purification  of  Water  —  Works  for  the  Distribution 
of  Water  —  Arrangement  of  Works  —  Systems  of  Operation  —  Comparison  of  the 
Various  Systems  —  Existing  Works  as  Affecting  Choice  —  The  Dual  System 206 

PRINCIPLES  OF  ECONOMIC  CONSTRUCTION.  —  The  General  Problem  —  Methods  of  Com- 
paring Cost  —  Method  of  Capitalization  —  Method  of  Annual  Expense  —  Depre- 
ciation of  Structures  —  Annuity  Table  —  Provision  for  the  Future  —  Estimates  of 
Cost  —  Literature ; 21^ 

CHAPTER   XII. 

HYDRAULICS. 

Purpose  of  the  Chapter  —  Units  of  Measure  —  Notation  —  Weight  of  Water  —  Pressure 

of  the  Atmosphere  —  Vapor  Tension  of  Water  —  Pressure  of  Water 223 

FLOW  OF  WATER  THROUGH  ORIFICES.  —  Form  and  Proportion  of  Orifices  —  Flow 
through  Small  Orifices  —  Large  Rectangular  Vertical  Orifices  —  Circular  Vertical 
Orifices 226 

FLOW  OF  WATER  OVER  WEIRS.  —  Sharp-crested  Weirs  —  Submerged  Weirs  —  Weirs  of 

Various  Sections 228 

FLOW  OF  WATER  THROUGH  PIPES.  —  General  Relations  between  Velocity  and  Pressure  — 
Nature  of  Fluid-friction  —  General  Formulas  —  Coefficients  and  Formulas  for  Cast- 
iron  Pipes — Comparison  of  Various  Formulas  —  Diagram  Recommended  for  Use 
in  the  Design  of  Distributing  Systems  —  Effect  of  Age  of  Service  on  Loss  of  Head  — 
Friction  Loss  in  Service-pipes  —  Coefficients  for  Riveted  Pipes  —  Friction  Loss  in 
Wood-stave  Pipe  —  Measurement  of  Flow  through  Large  Pipes  —  Minor  Losses  of 
Head  —  Hydraulics  of  Fire-streams  —  Friction  Loss  in  Fire-hydrants  —  Water- 
hammer  235 

FLOW  OF  WATER  IN  OPEN  CHANNELS.  —  Formulas  Employed  —  Measurement  of  Water 

Flowing  in  Open  Channels 256 

A.  WORKS   FOR  THE  COLLECTION  OF  WATER. 

CHAPTER  XIII. 

RIVER   AND   LAKE   INTAKES. 

General  Conditions 259 

RIVER  INTAKES.  —  Location  —  Intakes  in  Large  Streams  Varying  Little  in  Stage  — 
intakes  in  Streams  of  Ordinary  or  Great  Variation  in  Water-level  —  Intake-works  for 

Gravity-supplies 259 

LAKE  INTAKES.  —  Location  —  The  Intake  Conduit  —  Protection-works  —  Obstruction 

of  Intakes  by  Anchor-ice  —  Literature 266 


CONTENTS.  XI 


CHAPTER    XIV. 

WORKS   FOR  THE   COLLECTION   OF  GROUND-WATER. 

PAGE 

Classification 274 

WORKS  FOR  UTILIZING  THE  FLOW  FROM  SPRINGS.  —  Objects  to  be  Attained  —  Ordinary 

Forms  of  Collecting-basins  —  Methods  of  Increasing  the  Flow 274 

THE  HYDRAULICS  OF  WELLS.  —  A .  Principles  Governing  the  Flow  into  Ordinary  Wells 
and  Galleries  —  General  Form  of  Ground-water  Surface  —  Derivation  of  Formula 
for  Flow  —  Calculation  of  Flow  —  Effect  on  the  Yield  of  a  Change  in  the  Various 
Elements  —  Flow  into  Galleries  —  B.  Principles  Governing  the  Flow  into  Artesian 
Wells  —  C.  Considerations  of  General  A  p plication  —  Pipe-friction  and  other  Losses 
of  Head  —  Effect  of  Depth  of  Well  —  Mutual  Interference  of  a  Number  of  Wells  — 
Determination  of  Yield  by  Tests  —  Wells  Sunk  into  Strata  in  which  the  Flow  Takes 
Place  through  Fissures 277 

CONSTRUCTION  OF  WELLS.  —  Forms  of  Construction  —  Location  of  Wells  —  Relative 
Advantages  of  Large  and  Small  Wells  —  Large  Open  Wells  —  Size  and  Depth  of 
Wells  —  Construction  —  Yield  —  Examples  —  Shallow  Tubular  Wells  —  Methods 
of  Sinking —  Strainers  —  General  Method  of  Operating  a  Well-system  —  Arrange- 
ment and  Spacing  of  Wells  —  Size  of  Well  —  Details  of  Connections  —  The  Clogging 
of  Wells  —  Tests  —  Yield  —  Examples  —  Deep  and  Artesian  Wells  —  Comparison 
with  Shallow  Wells  —  Boring  Deep  Wells  —  Casing  of  Wells  —  Cost  —  Arrange- 
ment —  Size  and  Spacing  —  Methods  of  Operation  —  Examples  of  Artesian-well 
Plants  —  Yields  —  Failure  of  Wells 292 

HORIZONTAL  GALLERIES  AND  WELLS.  —  Filter-galleries  —  Examples  —  Tunnels  in  Rock 
—  Wells  and  Galleries  near  Streams  —  Horizontal  or  Push  Wells  —  Filter-cribs  — 
Literature.  . . 318 


CHAPTER    XV. 

IMPOUNDING-RESERVOIRS. 

CAPACITY.  —  Use  and  Value  of  Storage  —  Factors  to  be  Considered  —  Appropriation  of 
Surface-waters  —  Computation  of  Storage  —  Storage  Calculation  from  the  Sudbury 
River  Records  —  Capacity  of  a  System  of  Reservoirs 327 

LOCATION  AND  CONSTRUCTION.  —  Considerations  Affecting  Location  —  Surveys  and 
Preliminary  Work  —  Depth  of  Reservoir  —  Cleaning  the  Site  —  Shallow  Flowage  — 
Maintenance  —  Literature 333 

CHAPTER  XVI. 

EARTHEN  DAMS. 

GENERAL  CONSIDERATIONS.  —  The  Requisites  of  a  Dam  —  Kinds  of  Dams  —  The  Dam 

as  a  Porous  Structure 339 

THE  EARTHEN  EMBANKMENT.  —  Advantages  and  Requisite  Conditions  —  Forms  of 
Construction  —  Stability  of  the  Various  Forms  of  Embankments  —  Material  for 
Embankments  —  Core-walls  —  Embankment-slopes  —  Height  above  Water-line  — 
Width  of  Top  —  Preparing  the  Foundation  —  Construction  of  the  Embankment  — 
Hydraulic  Dam-construction  —  Slope-protection  —  Embankments  and  Founda- 
tions of  Porous  Material  —  Outlet-pipes  —  Gate-chambers  —  Valves  and  Sluice- 
gates —  Waste-weirs  —  Care  of  Floods  during  Construction  —  Cost  —  Literature. .  341 


Xii  CONTENTS, 


CHAPTER    XVII. 

MASONRY    DAMS. 

PAGB 

THE  DESIGN.  —  General  Conditions  —  The  External  Forces  Acting  upon  a  Dam  —  Inter- 
nal Stresses  —  Conditions  of  Stability  —  Allowable  Pressure  —  Weight  of  Masonry 

—  A.  Stability  of  Low  Dams  —  Calculation  of  Section  —  B.  Stability  of  High  Dams 

—  General  Statement  of  the  Problem  —  Wegmann's  Method  of  Determining  the 
Profile  —  Effect  of  Approximations  in  the  Foregoing  Treatment  —  Use  of  a  Standard 
Profile  —  Approximate  Triangular  Profile  —  Forces  not  Considered  in  the  Preceding 
Analysis  —  Top  Width  and  Height  above  Water-line  —  Curved  Dams 374 

CONSTRUCTION.  —  The  Foundation  —  Construction  of  the  Masonry  —  Imperviousness 

—  Earth  Backing  for  Masonry  Dams  —  Draw-off  Arrangements  —  Masonry  Waste- 
weirs  —  Other     Examples    of    Dams  —  Dams    of   the    Buttress    Type  —  Cost  — 
Literature 392 

CHAPTER  XVIIL 
TIMBER  DAMS;  STEEL  DAMS;  LOOSE-ROCK  DAMS. 

TIMBER  DAMS.  —  Use  of  Timber  Dams  —  Examples  of  Timber  Dams 41  a 

LOOSE-ROCK  DAMS.  —  Examples 414 

STEEL  DAMS.  —  Steel  Cores  —  Dams  Wholly  of  Steel  —  Literature 415 

B.  WORKS  FOR  THE  PURIFICATION  OF  WATER. 

CHAPTER  XIX. 

OBJECTS  AND  METHODS  OF  PURIFICATION. 

Purification  of  Water  for  Manufacturing  Purposes  —  Purification  of  Water  for  Domestic 

Purposes  —  Outline  of  Methods  of  Purification  Employed  —  Literature 419 

CHAPTER  XX. 

SEDIMENTATION. 

The  Character  of  the  Suspended  Matter  —  Limitations  of  Artificial  Sedimentation  — 

Methods  of  Sedimentation 424 

PLAIN  SEDIMENTATION.  —  Action  of  Subsidence  —  Time  Required  for  Subsidence  — 
Bacterial  Efficiency  of  Sedimentation  —  Bacterial  Content  of  Reservoir  Sediment  — 
Experimental  Data  on  the  Action  of  Finely  Divided  Matter  in  Water 426 

SEDIMENTATION  WITH  COAGULATION.  —  The  Use  of  Coagulants  —  The  Action  of  Various 
Coagulants  —  The  Amount  of  Chemical  Required  —  Time  of  Subsidence  —  Effi- 
ciency of  Sedimentation  with  Coagulation 431 

SETTLING-BASINS.  —  Methods  of  Operation  —  Number  and  Size  of  Basins  —  Form  of 
Basin  —  Arrangement  of  Pipes,  Continuous-flow  System  —  Arrangement  of  Pipes, 
Intermittent  System  —  Drain-pipes  —  Clear-water  Well  —  Preparation  and  Control 
of  Coagulant  —  Examples  of  Settling-basins  —  Literature 438 

CHAPTER  XXI. 

SLOW  SAND  FILTRATION. 

Historical  —  Types  of  Sand  Filters '. 450 

THEORY  AND  EFFICIENCY  OF  FILTRATION.  —  General  Results  of  Filtration  —  Theory  of 
Filtration  —  Bacteria  in  the  Effluent  —  Efficiency  of  Filtration  —  Passage  of  Bac- 
teria Confirmed  by  Disease  Outbreaks  —  Death-rates  as  Measures  of  Efficiency 453 


CONTENTS.  Xlll 

PAGE 

CONSTRUCTION  AND  OPERATION.  —  Rate  of  Filtration  —  Capacity  —  Number  and  Size 
of  Beds  —  General  Construction  —  Necessity  of  Covering  Filters  —  The  Filtering- 
sand  —  Friction  in  the  Sand-layer  —  Thickness  of  Sand-bed  —  The  Depth  of  Water 
on  the  Filter  —  Drainage  Systems  —  Loss  of  Head  in  the  Drainage  System  —  Maxi- 
mum Total  Loss  of  Head  —  Inlet-pipes  —  Outlet-pipes  and  Apparatus  for  Regu- 
lating the  Head  —  Automatic  Regulation  —  Other  Pipes  and  Valves  —  General 
Arrangement  of  Piping  —  Pure-water  Reservoir  —  Cleaning  Filters  —  Period  of 
Service  —  Effect  of  Scraping  on  Efficiency  of  Filtration  —  Sand-washing  —  Bac- 
terial Control  of  Filter  Operations  —  Preliminary  Treatment  —  Double  Filtration  — 
Intermittent  Filtration  —  Literature  —  Cost  of  Filters  —  Cost  of  Operation 461 

CHAPTER  XXII. 

RAPID    SAND    FILTRATION. 

General  Description  of  the  Rapid  Sand  Filter  —  Types  of  Construction  —  Principles  of 
Operation  —  Experiments  on  Rapid  Filters  and  Results  of  Operation  —  General 
Arrangement  of  Plant — Details  of  Construction  and  Operation — Cost — Literature  502 

CHAPTER  XXIII. 

MISCELLANEOUS   PURIFICATION  PROCESSES. 

Special  Forms  of  Filters  —  Aeration  —  Softening  of  Water  —  Chemistry  of  Water- 
softening  —  General  Features  —  Softening  of  Water  for  Boiler  Use  —  Bacterial 
Efficiency  of  the  Softening  Process  —  Removal  of  Iron  from  Waters  —  Application 
of  Electricity  to  Water-purification  —  The  Anderson  Revolving  Purifier —  Steriliza- 
tion and  Distillation  —  Purification  by  the  A  ddition  of  Chemicals  —  Ozone  —  Chlo- 
rinated Lime  —  Peroxide  of  Hydrogen  —  Copper  Sulphate  —  Literature  .........  530 

C.  WORKS  FOR  THE  DISTRIBUTION  OF  WATER. 

CHAPTER   XXIV. 

PIPES  FOR  CONVEYING  WATER. 

Materials  Employed  —  Stresses  to  be  Considered 551 

CAST-IRON  PIPE.  —  General  —  Thickness  and  Weight  of  Cast-iron  Pipe  —  Joints  — • 
Special  Castings  —  Material  and  Method  of  Manufacture  —  Durability  of  Cast-iron 
Pipe 555 

WROUGHT-IRON  AND  STEEL  PIPE.  —  Advantages  —  Quality  of  the  Material  —  Thickness 

of  Shell — Joints  —  Special  Details — Coating  of  Steel  Pipe — Durability  of  Steel  Pipe  565 

WOODEN  PIPE.  —  Advantages  —  Bored  Pipe  —  Stave  Pipe  —  General  Requirements  for 
Staves  and  Bands  —  Size  of  Bands  —  Spacing  of  Bands  —  Coupling-shoes  — 
Specials  —  Leakage  and  Durability  of  Wooden  Pipe. . 571 

OTHER  MATERIALS  EMPLOYED  FOR  WATER-PIPE.  —  Cement  Pipe  - —  Vitrified-clay  Pipe 

—  Materials  for  Service  Pipes  —  Literature 581 

CHAPTER  XXV. 

CONDUITS  AND  PIPE-LINES. 

Classes  of  Conduits  —  Capacity  of  Conduits  —  Single  or  Double  Conduits  —  Location 

of  Conduits 586 

CANALS.  —  Use  of  Canals  —  Slopes  and  Velocities  —  Cross-sections  —  Other  Details  — 

Flumes 589 


XIV  CONTENTS. 

PAGE 

MASONRY  AQUEDUCTS.  —  Advantages  of  Masonry  Aqueducts  —  Size  of  Cross-section, 
Velocity  and  Slope  —  Materials  Employed  —  Form  and  Stability  of  Section  — 
Constructive  Features  —  Special  Details — Tunnels  —  Aqueducts  of  Vitrified  Pipe  . .  593 

PIPE-LINES.  —  The  General  Design  —  Material  to  be  Employed  —  The  Profile —  Pres- 
sures to  be  Assumed  —  Calculation  of  Size  of  Pipe  —  Construction  —  Plan  and  Profile 

—  Trenching — Foundations  —  Laying  of  Pipe  —  Testing  and  Inspection  —  Cover- 
ing of  Pipe  —  Appurtenances  and  Special  Details  —  Provision  for  Expansion  and 
Contraction  —  Manholes  —  Stop-valves  —  Air-valves  —  Blow-off    Valves  —  Seii- 
acting  Shut-off    Valves  —  Check-valves  —  Pressure-regulation  Devices  —  Terminal 
Arrangements  —  Crossings  —  Bridges  —  Protection  of  Exposed  Pipes  —  Submerged 
Pipes 601 

COST  OF  CONDUITS  AND  PIPE-LINES.  —  Canals  and  Masonry  Aqueducts  —  Pipe-lines  — 

Literature 624 

CHAPTER  XXVI. 

PUMPING-MACHINERY. 

Introductory  —  Energy  Expended  in  Pumping  Water  —  Work  and  Power  Equivalents  — 

Classification  of  Energy  Losses 630 

SOURCES  OF  POTENTIAL  ENERGY.  —  Available  Sources  —  Fuel  —  Water-power. 636 

GENERATION  AND  CONVERSION  OF  ENERGY.  —  Ordinary  Efficiency  of  Generators  and 
Motors  —  The  Steam-boiler  —  The  Steam-engine  —  Use  of  Steam  Expansively  — 
Use  of  Condensers  —  Average  Steam  Consumption  —  Effect  of  Operating  at  Part 
Load  —  Heat-engines 637 

THE  TRANSMISSION  OF  ENERGY.  —  Methods  of  Transmission  and  General  Efficiencies  — 
Direct  Connection  —  Shafting  —  Gearing  —  Belts  —  Rope  Transmission  —  Wire- 
rope  Transmission  —  Pneumatic  Transmission  —  Hydraulic  Transmission  — Elec- 
trical Transmission 644 

THE  PUMP  IN  GENERAL.  —  Classification  of  Pumps  —  (i)  Displacement  Pumps  —  Recip- 
rocating Pumps  —  The  Steam-pump  —  Rotary  Pumps  —  Air-  and  Steam-displace- 
ment Pumps  —  Continuous-flow  Pumps  —  (2)  Impeller  Pumps  —  Action  of  Impeller 
Pumps  —  The  Centrifugal  Pump  —  Jet-pumps  —  (3)  Impulse  Pumps  —  (4) 
Bucket  Pumps 649 

PUMP  DETAILS.  —  General  Rules  —  Valves  —  Air-  and  Vacuum-chambers  —  Suction- 
pipes  —  Location  of  Pumping-machinery  with  Respect  to  the  Level  of  the  Water 
Drawn  From 663 

DUTY  AND  EFFICIENCY  OF  PUMPING-MACHINERY.  —  Measures  of  Duty  —  Ordinary  Duty 
and  Efficiency  of  Pumping-machinery  —  Methods  of  Analyzing  Power  Losses  — 
Capacity  of  Pumping-machinery  —  Comparison  of  the  Economy  of  Different  Designs 

—  Examples  —  Literature 670 

CHAPTER  XXVII. 

DISTRIBUTING  AND   EQUALIZING  RESERVOIRS. 

Office  —  Kinds  of  Reservoirs  —  Capacity  —  Location  —  Elevation 689 

EARTHEN  AND  MASONRY  RESERVOIRS.  —  Form  and  Arrangement  —  Depth  —  Embank- 
ment Construction  —  Linings  —  Masonry  Walls  —  Arrangement  of  Pipes,  Valves, 

etc.  —  Covered  Reservoirs  —  Masonry  Reservoirs  —  Cost 694 

STAND-PIPES  AND  TANKS.  —  Capacity  —  Location  —  Stand-pipes  —  General  Propor- 
tions—  Forces  and  Stresses  —  Material  Employed  —  Plate  Thickness  —  Riveting 

—  Bottom    Details  —  Foundation    and   Anchorage  —  Pipes   and    Valves  —  Other 


CONTENTS.  XV 

PAGE 

Details  —  Encased  Stand-pipes  —  Elevated  Tanks  —  Economy,  Form,  and  Propor- 
tions —  Stresses  in  Tank  —  The  Tower  —  Anchorage  —  Inlet  Pipe  —  Masonry 
Towers  —  Wooden  Tanks  —  Reinforced  Concrete  Tanks  —  Storage  of  Water  under 
Pressure  —  Literature 711 

CHAPTER  XXVIII. 

THE    DISTRIBUTING    SYSTEM. 

General  Requirements  —  The  Pressure  Required  —  Number  and  Size  of  Fire-streams  — - 
Location  of  Hydrants  —  General  Arrangement  of  the  Pipe  System  —  Maximum 
Rates  of  Supply  for  Different  Areas  —  Velocities  of  Flow  for  Fire  Supplies  —  Loss  of 
Head  in  Distributing-pipes  —  General  Problems  Pertaining  to  the  Flow  through 
Compound  Pipes  —  Calculation  of  the  Pipe  System  —  Separate  Services  for  Different 
Zones  of  Elevation] —  Location  of  Pipes  and  Valves  —  Hydrants  —  Depth  of  Cover- 
ing for  Distributing-pipes  —  Service  Connections  —  Other  Details  —  Special  Fire- 
protection  Systems  —  Records  and  Maps  —  Literature „ . .  742 

CHAPTER  XXIX. 

OPERATION  AND  MAINTENANCE. 

Conduits  and  Pipe-lines  —  Pumping-stations  —  Distributing-reservoirs,  Stand-pipes,  and 
Tanks 7;3 

THE  DISTRIBUTING  SYSTEM.  —  Mains  and  Service-pipes  —  Valves  and  Hydrants  — 

Detection  and  Prevention  of  Waste  —  Meters „ . .  781 

FINANCIAL.  —  General  Considerations  —  Expenses  and  Charges  to  be  Met  —  Relative 
Cost  of  Different  Services  —  Sources  of  Revenue  —  Water  Rates  —  Literature 789 


PUBLIC  WATER-SUPPLIES. 


CHAPTER   I. 

INTRODUCTION. 

HISTORICAL   SKETCH. 

i.  Water-supplies  in  Ancient  Times. — The  earliest  method  of  artifi- 
cially obtaining  a  water-supply  was  doubtless  by  the  digging-  of  wells. 
These  were  naturally  at  first  mere  shallow  cavities  scooped  out  of  the 
ground  in  moist  places,  such  as  are  used  at  the  present  time  by  savage 
tribes ;  but  as  necessity  arose  and  the  use  of  implements  developed, 
these  wells  were  gradually  deepened. 

The  digging  of  wells  dates  from  a  very  early  period.  In  the 
vicinity  of  the  pyramids  there  still  exist  wells  which  were  in  use  when 
those  great  works  were  constructed.  Joseph's  well  at  Cairo  is  perhaps 
the  most  famous  of  all  ancient  wells.  It  is  a  remarkable  work  and 
exhibits  in  a  high  degree  the  skill  of  the  people  of  ancient  Egypt  in 
matters  pertaining  to  construction.  It  is  excavated  in  solid  rock  to  a 
depth  of  297  feet  and  consists  of  two  stories  or  lifts.  The  upper  shaft 
is  1 8  by  24  feet,  and  165  feet  deep;  the  lower  is  9  by  15  feet  and 
reaches  to  a  further  depth  of  1 30  feet.  Water  is  raised  in  two  lifts  by 
means  of  buckets  on  endless  chains,  those  for  the  lower  level  being 
operated  by  mules  in  a  chamber  at  the  bottom  of  the  upper  shaft,  to 
which  access  is  had  by  means  of  a  spiral  pathway  winding  about  the 
well.* 

Frequent  mention  is  made  by  the  old  historians  of  important  wells 
in  ancient  Greece,  and  remains  of  such  works  are  numerous  in  Assyria, 
Persia,  and  India.  Probably  the  deepest  wells  were  dug  by  the 
Chinese,  depths  of  1500  feet  or  more  being  reached  by  methods 
almost  identical  with  those  now  in  common  use. 

*  Ewbank's  Hydraulics,  p.  45. 


2  INTRODUCTION. 

Besides  the  digging  of  wells,  the  ancients  executed  many  works 
for  the  storage  and  conveyance  of  water.  In  Jerusalem  underground 
cisterns  were  built  for  the  storage  of  rain-water;  and  other  reservoirs 
were  constructed  near  the  city  to  store  the  water  which  was  brought 
thither  in  masonry  conduits.  Aqueducts  were  also  built  in  ancient 
Greece,  one  mentioned  by  Herodotus  as  built  to  supply  the  city  of 
Samos  being  still  in  good  preservation.  Some  of  these  ancient 
aqueducts  included  inverted  siphons  of  cut-stone  blocks.  Ruins  of 
extensive  underground  reservoirs  are  to  be  found  on  the  site  of  ancient 
Carthage,  which  it  is  believed  were  constructed  prior  to  the  capture 
of  the  city  by  the  Romans.  Works  for  irrigation  in  Egypt,  Assyria, 
and  India  were  established  on  an  immense  scale,  one  reservoir  in 
Egypt,  Lake  Maeris,  having  had,  it  is  said,  an  area  of  30,000  acres. 
In  the  Presidency  of  Madras,  India,  the  English  found  at  the  time  of 
their  occupation  about  50,000  reservoirs  for  irrigation  purposes,  the 
construction  of  which  had  involved  the  building  of  30,000  miles  of 
earth  embankment.  Many  of  these  reservoirs  were  doubtless  of  ancient 
construction. 

2.  Water-works  of  the  Romans — Among  ancient  systems  of  water- 
supply  the  works  of  no  other  nation   equaled   those  of  the  Romans, 
either  in  point  of  size  or  number ;   and  no  city  in  the  Roman  Empire 
was  more  abundantly  supplied  than  the  city  of  Rome  itself.      Previous 
to  about  312  B.C.  Rome  obtained  its  water  from  the  Tiber  and  from 
springs   and  wells   in  the    immediate   vicinity,    but  this   water   finally 
became  so  badly  polluted  that  a  purer  supply  was  sought  from  distant 
sources. 

3.  Aqueducts. — The   conveyance  of  water  from  these  new  sources 
necessitated  the  construction    of  long  conduits   or  aqueducts.      These 
were  often    led  through  hills  in  tunnels,    or  carried    over  valleys   on 
long  lines  of  arches  that  are  to  this  day  the  object  of  our  wonder  and 
admiration.      The  Romans,    and  indeed  the  Greeks,   well  understood 
the  principle   of  the  inverted   siphon,  and  used  it  on  occasion;  as,  for 
example,    in  the  works  of  Lyons,    France,  where  they  constructed  a 
siphon  consisting  of  nine  miles   of  lead   pipe  from  12  to    18  inches  in 
diameter,  working  under  a  2OO-foot  head.      The  only  materials,  how- 
ever,   which    could   be  used   for  this   purpose  were    stone,    lead,    and 
pottery,  iron  pipes  being  unknown;  and   the   engineers   of  that  time 
adopted  what  was  doubtless  the  most  economical  method  of  crossing 
depressions,  that  is,  by  carrying  the  conduit  on  arches. 

The  first  aqueduct  built  to  supply  Rome  was  called  the  Aqua 
Appia,  after  its  builder,  Appius  Claudius.  It  was  constructed  about 


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312  B.C.  and  had  a  length  of  about  u  miles.  A  second  was  built 
about  270  B.C.  with  a  length  of  39.5  miles,  1080  feet  of  which  was 
supported  on  arches.  Others  were  constructed  from  time  to  time  until, 
with  the  completion  of  the  Anio  Novus  about  52  A.D.,  there  were  nine 
aqueducts  furnishing  water  to  the  city  of  Rome.  These  are  described 
in  detail  by  Frontinus,  a  Roman  surveyor  and  water  commissioner,  in 
a  work  written  A.D.  97,*  in  which  he  also  gives  much  interesting 
information  concerning  the  various  matters  coming  within  his  official 
duties.  Five  more  aqueducts  were  constructed  after  the  time  of 
Frontinus,  the  last  dating  about  305  A.D.  The  aggregate  length  of 
the  fourteen  was  359  miles;  and  aggregate  length  of  arches,  50  miles. 
In  cross-section  the  aqueducts  of  Rome  varied  from  3  to  8  feet  in 
height  by  2^  to  5  feet  in  width,  and  were  built  with  vertical  sides  and 
flat  or  arched  roofs.  The  interior  was  finished  with  great  care  to 
secure  imperviousness,  but  in  spite  of  this  they  were  constantly  getting 
out  of  repair. 

The  Romans  not  only  built  works  for  supplying  their  chief  city, 
but  also  executed  many  works  of  great  importance  in  all  parts  of  the 
Empire,  as  at  Paris  and  Lyons  in  France,  Metz  in  Germany,  and 
Segovia  and  Seville  in  Spain.  One-half  of  the  aqueduct  at  Metz  is  still 
in  use,  although  built  in  the  year  130  A.D.  That  at  Nimes,  France, 
is  famous  for  its  great  aqueduct  bridge,  the  Pont  du  Gard,  where  three 
tiers  of  arches  rise  to  a  maximum  height  of  158  feet. 

4.  Distribution  System. — The  distribution  of  water  in  this  age  was 
by  no  means  general.      In  Rome  the  water  from  the  aqueducts  first 
passed  into  large  cisterns,  and  from  these  was  distributed  through  lead 
pipes  to  other  cisterns,  and  to  the  fountains,  baths,  and  various  public 
buildings,  and  to  private  consumers.      The  last  class  was  very  limited 
in  number,  most  of  the  people  being  obliged  to  get  their  supply  from 
the  public  fountains.      Each  service  required  a  separate  pipe  leading 
from  the  distributing  cistern,  and  the  amount  of  water  to  which  the 
consumer  was  entitled  was  measured  by  means  of  a  short  tube  of  speci- 
fied diameter.      At  the  time  of  Constantine  there  were  in  Rome    1 1 
great   thermae,    926    public    baths,     1212    public    fountains,    and    247 
reservoirs,  t 

5.  Quantity  of  Water  Supplied. — The  amount  of  water  supplied  to 
ancient  Rome  was  very  liberal.      It  has  been  estimated  as  high  as  400 
million  gallons  per  day  at  the  time  of  Frontinus,  but  after  a  careful 
study  of  the  evidence,  and  allowing  for  the  fact  that  usually  some  of 


*  See  reference  (13),  p.  14. 

\  Lanciani.     The  Ruins  and  Excavations  of  Ancient  Rome  (1897),  p.  56. 


8  INTRO D  UCTION. 

the  aqueducts  were  out  of  repair,  Mr.  Herschel  estimates  the  probable 
quantity  delivered  within  the  city  at  about  50  million  gallons  daily,  or 
about  50  gallons  per  capita.  Even  at  the  latter  figure  the  supply  must 
be  considered  as  very  liberal. 

6.  Quality  of  Water. — The  ancients  had  some  clear  notions  con- 
cerning the  quality  of  water-supplies.      In  his  time,  Hippocrates  knew 
something  of  the  danger  of  drinking  water  which  had  passed  through 
lead  pipes,  and  even  recommended  the  boiling  and  filtering  of  polluted 
water.      At   Rome   the    different    aqueducts    brought   waters    of  quite 
different  qualities.      The  best  was  used  for  domestic  purposes  and  the 
other  for  baths  and  various  public  purposes,  the  water  from  one  aque- 
duct being  of  such  poor  quality  that  as  a  rule  it  was  used  only  for 
irrigation   and   for  supplying  the  basin  of  a  marine   circus.      In  some 
cases   water   was  passed    through  artificial   reservoirs  to    purify   it  by 
sedimentation. 

7.  The  Middle  Ages. — The  fall  of  Rome  brought  with  it  the  destruc- 
tion of  the  aqueducts  and  the  general  neglect  of  the  entire  subject  of 
water-supply.      The   Popes    maintained    with    various   interruptions   a 
supply  to  the  city  of  Rome,  and   a  few  other  important  cities  were 
scantily  provided  with  water.      In  other  places,  however,  the  supplies 
entirely  ceased ;  and  it  is  said  that  in  some  cases  the  inhabitants  even 
forgot  the  use  to  which  the  old  works  had  been  put. 

The  terrible  ravages  of  pestilence  during  the  Middle  Ages  were 
doubtless  due  in  large  measure  to  the  use  of  grossly  polluted  water, 
and  it  was  not  until  about  the  end  of  the  sixteenth  century  that  general 
improvement  began  to  be  made  in  sanitary  matters.  However,  as 
exceptions  to  this  there  should  be  mentioned  the  construction  of  a  few 
important  works  in  Spain  by  the  Moors,  such  as  those  at  Cordova  in 
the  ninth  century,  and  the  repair  of  the  Roman  aqueduct  at  Seville  in 
1172. 

Paris  depended  entirely  on  the  river  Seine  for  its  water-supply  until 
a  small  aqueduct  was  constructed  in  1183,  but  as  late  as  1550  the 
supply  amounted  to  only  one  quart  per  head  per  day.  In  London 
small  quantities  of  spring-water  were  brought  to  the  city  as  early  as 
1235  by  means  of  lead  pipes  and  masonry  conduits.  The  first  pump 
was  erected  on  the  old  London  bridge  in  1582  for  the  purpose  of 
supplying  the  city  through  lead  pipes.  In  Germany  water-works  were 
constructed  as  early  as  1412,  and  pumps  were  introduced  in  Hanover  in 
1527.  Mention  should  here  be  made  also  of  the  aqueduct  of  Zempola 
in  Mexico,  constructed  by  a  Franciscan  monk  between  1553  and  i57°> 
which  for  two  centuries  served  to  convey  water  from  Zempola  to 


HISTORICAL   SKETCH.  9 

Otuinba.      It    had   a   length   of  27.8   miles    and   included   three   arch 
bridges  of  a  maximum  height  of  124  feet.* 

8.  Development  of  Modern  Water-works  in  Europe. — During  the 
seventeenth  and  eighteenth  centuries  progress  was  slow,  and  confined 
mainly  to  the  cities  of  Paris  and  London.  Pumps  operated  by  water- 
power  were  erected  in  Paris  in  1608.  The  aqueduct  of  Arcueil  was 
completed  in  1624  and  delivered  about  200,000  gallons  per  day,  but 
at  the  end  of  the  seventeenth  century  the  supply  to  Paris  was  as  yet 
only  2^  quarts  per  head.  In  London  various  pumps  were  erected  on 
the  bridge  from  time  to  time  which  drew  their  supply  from  the  river 
and  were  operated  by  the  current.  In  1619  the  New  River  Company 
was  incorporated  and  laid  its  pipes  throughout  the  city.  It  received 
its  supply  from  the  New  River,  and  for  the  first  time  the  general  prin- 
ciple was  adopted  of  supplying  each  house  with  water.  This  company 
still  supplies  a  part  of  London. 

The  application  of  steam  to  water-pumping  in  the  eighteenth  cen- 
tury gave  a  great  impetus  to  the  development  of  water-works. 
Probably  the  first  use  of  steam  for  this  purpose  was  in  London  in  1761. 
A  steam-pump  was  also  erected  in  Paris  in  1781  and  another  in  1783, 
and  a  second  in  London  in  1787.  In  all  these  instances  the  supplies 
were  taken  directly  from  the  adjacent  rivers. 

Since  1800  the  supplies  of  both  London  and  Paris  have  been 
greatly  augmented  from  various  sources.  Some  of 'the  works  are  very 
noteworthy,  as,  for  example,  the  two  aqueducts,  of  respectively  8 1 . 5 
and  1 08  miles  in  length,  constructed  to  bring  spring-water  to  the  city 
of  Paris. 

In  1890  the  supply  of  Paris  was  about  65  gallons  per  capita,  of 
which  about  three-fourths  was  drawn  from  rivers  and  used  for  street- 
washing  and  other  public  purposes,  while  only  one-fourth,  or  about  16 
gallons  per  capita,  was  drawn  from  springs  and  used  for  domestic 
purposes.  The  latter  quantity  having  been  found  inadequate,  an 
additional  supply  of  about  30  million  gallons  was  brought  to  the  city 
in  1892  by  means  of  another  aqueduct  63  miles  long,  thus  giving  an 
additional  supply  of  about  12  gallons  per  head.  A  still  further  addi- 
tion of  some  i  5  million  gallons  has  recently  been  provided  for. 

The  water-supply  of  London  was  brought  under  municipal  manage- 
ment in  1904,  previous  to  which  time  the  city  was  supplied  by  eight 
separate  companies.  About  55  per  cent  of  the  supply  is  from  the 
Thames,  25  per  cent  from  the  Lea,  and  20  per  cent  from  springs  and 
wells  in  the  chalk.  All  river-water  is  filtered.  The  total  population 

*  Eng.  News,  1888,  xx.  p.  2. 


I O  INTR  OD  UC  riON. 

supplied  is  about  6,000,000,  and  the  rate  of  consumption  is  about  40 
gallons  per  capita  daily. 

Notwithstanding  the  early  existence  of  public  water-supplies  in  a 
few  cities,  the  general  development  of  water-works  was  very  slow  in 
the  first  half  of  this  century ;  for  example,  as  late  as  1 864  there  had 
been  constructed  in  Germany  but  twenty-four  water-works.  During 
the  last  thirty  years,  however,  the  development  in  all  civilized  coun- 
tries has  been  very  great,  and  the  rate  of  growth  has  constantly  in- 
creased. 

9.  For  many  years  the  larger  pipes  were  usually  of  wood,  made 
by  boring   out   logs   to  a  diameter  of  6  or  7  inches.      Cast-iron  pipes 
came  into  general  use  about  1800;  and  in  1820  the  New  River  Com- 
pany of  London  replaced   its  wooden  mains  with  cast-iron  ones  at  a 
cost  of  $1,500,000.     At  one  time  this  company  had  about  400  miles  of 
wooden  pipe  in  use,  and   often  as  many  as  ten  lines  of  pipe  were  laid 
side  by  side  to  form  a  single  main. 

"When  water  first  began  to  be  supplied  to  each  house  it  was  thought 
quite  impracticable  to  furnish  a  continuous  supply.  Instead,  the  water 
was  turned  on  for  only  a  few  hours  in  the  twenty-four,  at  which  time 
the  consumers  were  obliged  to  lay  in  their  supply  for  the  day.  For 
sanitary  reasons,  and  as  a  matter  of  convenience,  the  constant-supply 
system  came  into  general  use  in  spite  of  the  many  arguments  against 
it.  It  was  introduced  in  London  in  1873,  but  as  late  as  1891,  35  per 
cent  of  the  total  supply  was  still  on  the  intermittent  system. 

In  Europe  the  question  of  quality  has  received  as  much  attention 
as  that  of  quantity.  Great  expense  is  borne  to  secure,  if  possible, 
water  from  springs  or  mountain  streams,  but  where  this  is  impractica- 
ble, efficient  purification  works  are  established.  In  the  early  part  of 
this  century  some  use  was  made  in  Paris  of  artificial  filters  for  purifying 
the  water  from  the  Seine;  but  filtration  on  a  large  scale  was  first 
inaugurated  by  the  Chelsea  Company  in  London,  which  in  1829  started 
the  first  large  sand  filter  similar  to  those  now  in  such  extensive  use. 
In  the  last  twenty-five  or  thirty  years  the  use  of  such  filters  has  rapidly 
extended  until  now  it  is  a  rare  exception  to  find  a  European  city  using 
unfiltered  surface-water. 

10.  Development    of  Water-works    in  the  United  States.  —  Early 
Works. — The  first  works  in  America  for  the  supply  of  water  to  towns 
were  those  of  Boston.      They  were  built  in  1652   and  served  to  bring 
water  by  gravity  from  springs.      The  first  instance  where  machinery 
was  used  was  at  Bethlehem,  Pa.,  the  works  of  which  were  put  into 
operation   June   20,    1754.      In  this  case  also  the  water  was  from   a 


HISTORICAL    SKETCH.  II 

spring,  which  is  still  in  use  as  a  water-supply.  It  was  forced  by  a 
pump  of  lignum  vitae  of  5 -inch  bore  through  hemlock  logs  into  a 
wooden  reservoir.  Eight  years  later  the  builder  of  these  works,  Hans 
Christ.  Christiansen,  replaced  the  wooden  pump  by  three  iron  ones  of 
4-inch  bore  and  1 8-inch  stroke  which  were  in  use  for  seventeen  years* 
The  next  works  constructed  were  probably  those  at  Providence,  R.  I., 
in  1772;  and  the  next,  those  at  Morristown,  N.  J.,  put  into  operation 
in  1791,  and  which  still  furnish  water  to  the  town. 

The  first  use  of  the  steam-engine  was  at  Philadelphia  in  1800. 
These  curious  engines  were  constructed  largely  of  wood,  even  the 
boiler  being  partly  of  this  material.  The  duty  was  4,790,000  foot- 
pounds per  100  pounds  of  coal.*  Steam  was  applied  to  New  York's 
water-supply  in  1804,  these  works  having  been  inaugurated  in  1799. 

In  the  United  States,  as  in  Europe,  wooden  pipes  were  at  first  used, 
but  it  is  stated  by  Chanute  t  that  cast-iron  pipes  were  used  in  Phila- 
delphia as  early  as  1804,  thus  antedating  by  a  few  years  their  use  in 
London. 

Besides  the  works  above  mentioned  some  others  were  constructed 
at  an  early  date,  the  total  number  in  1800  being  16.  Important  steps 
in  advance  were  made  by  the  construction,  in  1822,  of  the  enlarged 
works  at  Philadelphia  and,  somewhat  later,  of  the  gravity  works  of 
New  York  and  Boston. 

ii.  Progress  since  1850.  — The  principal  development  in  this 
country  has  taken  place  since  1850,  and  the  improvements  made  have 
been  very  marked.  Among  these  have  been  the  perfection  of  cast-iron 
pipe ;  the  improvements  of  pumping  machinery,  whereby  a  duty  is  now 
obtained  greatly  in  excess  of  what  was  considered  possible  twenty-five 
years  ago;  the  manufacture  of  the  smaller  pumps  on  a  commercial 
scale,  thus  greatly  reducing  the  cost  to  small  towns ;  the  adoption  of 
direct-pumping  systems  for  small  towns,  thus  also  in  many  cases  greatly 
reducing  first  cost;  and  the  development  of  the  ground  and  artesian 
water-supplies  in  the  Western  States.  The  public  water-supply  has 
now  come  to  be  so  much  of  a  necessity  that  it  is  rare  to  find  a  village 
of  2000  inhabitants  without  its  public  supply. 

The  growth  in  the  number  of  water-works  since  1850  is  shown  by 
the  following  table  taken  from  the  '  '  Manual  of  American  Water- 
works "  for  1891  and  1897.  It  gives  the  total  number  of  water-works 
in  existence  at  the  end  of  various  years,  and  the  number  built  in  each 
period. 

*  Illustrated  description  in  Eng.  News,  1887,  xvii.  p.  247. 
f  Trans.  Am.  Soc.  C.  E.,  1880,  ix.  p.  220. 


12 


IN  TROD  UCTION-. 


Number  of 

Number  of 

Year. 

Number  of 
Works. 

Works  Built 
in  each 

Year. 

Number  of 
Works. 

Works  Built 
in  each 

Period. 

Period. 

1850 

8l 

1875 

422 

17Q 

1855 

106 

23 

1880 

598 

I76 

1860 

136 

30 

1885 

1013 

415 

1865 

162 

26 

1890 

1878 

865 

1870 

243 

81 

I896 

3196 

I3l8 

The  new  works  built  between  1 890  and  1 896  were  of  course  mainly 
for  small  towns,  but  a  large  amount  of  work  has  also  been  done  each 
year  in  increasing  the  supplies  for  the  larger  cities.  In  1880  the  total 
population  supplied  was  11,809,231,  while  in  1890  it  was  22,814,061, 
nearly  one-half  of  the  increase  being  due  to  the  increase  in  population 
•of  cities  already  supplied  in  1880.  The  total  estimated  cost  of  the 
works  up  to  1891  was  $543,000,000;  number  of  miles  of  mains  32,400, 
taps  2,213,000,  and  hydrants  220,000. 

12.  Present  Conditions  and  Necessities. — As  regards  the  improve- 
ment in  the  quality  of  water  supplied  not  so  much  progress  has  been 
made  as  in  increasing  the  quantity,  and  in  this  respect  this  country  is 
far  behind  Europe.  A  large  proportion  of  our  largest  cities  use  water 
taken  directly  from  streams  more  or  less  polluted  by  sewage,  and  as 
yet  few  of  these  supplies  are  subjected  to  any  purification  process. 
The  problem  here  is  rendered  especially  difficult  by  reason  of  the  enor- 
mous quantities  of  water  used  by  American  cities  as  compared  with 
those  of  other  countries. 

From  this  statement  of  present  conditions  it  is  evident  that  the 
engineering  work  of  the  future  lies  principally  in  the  development  of 
new  and  better  sources  of  supply,  in  providing  increased  quantities  for 
our  rapidly  growing  cities,  and  especially  in  the  improvement  of  the 
quality  of  existing  supplies.  In  the  management  of  water- works,  also, 
much  needs  to  be  done  in  the  direction  of  waste  prevention,  both  to 
reduce  the  immediate  cost  of  operation  and  in  many  places  to  render  it 
possible  to  install  purification  works  at  a  reasonable  expense. 


VALUE   AND   IMPORTANCE   OF   A   PUBLIC   WATER-SUPPLY. 

13.  Domestic  Use. — The  most  important  use  of  a  public  water- 
supply  is  that  of  furnishing  a  suitable  water  for  domestic  purposes. 
The  absolute  necessity  of  a  supply  of  some  sort  for  such  purposes  in  a 
large  city  is  well  appreciated,  but  the  value  of  purity  is,  by  many,  not 
rated  as  high  as  it  should  be.  The  transmission  of  certain  diseases 


VALUE  AND    IMPORTANCE   OF  A    PUBLIC    WATER-SUPPLY.        13 

such  as  cholera  and  typhoid  fever  by  polluted  water  is  now  universally 
recognized,  and  the  value  to  a  city  of  a  pure  supply  when  compared  to 
one  constantly  polluted  by  sewage  can  scarcely  be  overestimated. 
Many  examples  of  the  benefits  arising  from  the  introduction  of  new  or 
improved  supplies  are  given  in  Chapter  X.  (f  \  \  \ 

A  public  supply  of  pure  water  is  of  great  value  not  only  in  large 
cities,  but  in  the  smaller  towns  and  villages.  Too  often  a  supply  for  a 
village  is  designed  with  almost  exclusive  reference  to  fire-protection, 
and  little  attention  is  paid  to  the  quality  of  the  water,  the  people 
expecting  to  depend  on  wells  as  before.  As  a  rule,  however,  a  good 
pure  water  is  quite  as  much  to  be  desired  in  this  case  as  for  a  city 
supply,  and,  if  provided,  will  in  many  cases  be  quite  as  fully  utilized. 

Another  highly  important  function  of  a  water-supply  is  that  of 
furnishing  the  necessary  flushing-water  for  a  sanitary  system  of 
drainage.  The  most  satisfactory  and  economical  method  yet  found 
for  disposing  of  the  organic  wastes  of  a  community  is  by  the  water- 
caVriage  system.  Such  a  sewerage  system  is  manifestly  of  but  slight 
value  to  the  public  at  large  without  the  coexistence  of  a  public  water- 
supply,  as  otherwise  the  necessary  water  for  the  flushing  of  closets — 
the  most  important  function  of  a  sewerage  system — can  be  afforded 
by  but  few. 

Besides  furnishing  an  improved  supply  from  the  sanitary  stand- 
point, a  public  works  may  often  be  made  to  furnish  a  water  which  for 
other  reasons  will  be  of  greatly  increased  value  to  the  domestic 
consumer ;  such  as  a  soft  water  in  place  of  a  hard  well-water — a  point 
of  very  considerable  importance  to  both  domestic  and  commercial 
users. 

14.  Commercial   Uses. — The    commercial    value  of  a  good  water- 
supply  is  appreciated  when  one  considers  the  large   number  of  manu- 
facturing interests  which  require  for  their  operation  large  quantities  of 
suitable     water.       Such     establishments     as     sugar-refineries,     starch- 
factories,  bleaching  and  dyeing  houses,  breweries,  chemical  works,  and 
various  other  factories  require  an   abundant  water-supply,  and  in  some 
cases  a  water  of  a  high  degree  of  purity.     The  question  of  water-supply 
indeed  often  determines  the  location  of  such  factories.      Large  quanti- 
ties are  also  used  for  operating   elevators,  for  boiler  purposes,  and  for 
many  other  uses  that  may  be  classed  as  commercial. 

15.  Public  Uses. — The  most  important  public  use  of  a  water-supply 
is  perhaps  in  extinguishing  fires.      The  economic  value  of  a  good  fire- 
protection  system  is  directly  shown  in  the  reduced  rates  of  insurance 
which  follow  its  introduction  or  improvement.     -Instead  of  distributing 


14  INTRO  D  UCTION. 

a  heavy  fire-loss  among  the  people  of  a  community  through  high  rates 
of  insurance  it  is  assuredly  much  better  economy  to  contribute  to  the 
maintenance  of  a  public  water-works,  which  at  the  same  time  provides 
a  suitable  water  for  other  purposes.  To  permit  of  the  establishment  of 
certain  classes  of  factories  it  is  absolutely  essential  that  an  efficient  fire- 
protection  be  furnished. 

Other  important  public  uses  of  a  water-supply  are  in  street-sprink- 
ling and  sewer-flushing,  in  furnishing  water  for  public  buildings,  and 
for  drinking  and  ornamental  fountains.  A  real  value  exists  in  the 
improved  appearance  which  may  be  given  a  city  by  the  use  of  water  in 
fountains  and  for  lawns  and  public  parks;  and  indeed  all  the  benefits 
accruing  from  a  good  water-supply  act  indirectly  to  increase  the 
desirability  of  a  town  for  many  purposes  and  to  enhance  the  value  of 
the  property  therein. 

LITERATURE. 

1.  Ewbank.      Hydraulic    and    other   Machines   for  Raising   Water.      New 

York,  1876. 

2.  d'Avigdor.      Water-works,    Ancient    and    Modern.      Engineering,    1876, 

xxi.  p.  403. 

3.  Grahn.     Statistik  der  stadtischen  Wasserversorgung.     Munich,  1878. 

4.  Chanute.     Annual  Address.    Trans.  Am.  Soc.  C.  E.,  1880,  ix.  p.  217. 

5.  Higgins.     The  Old  Water-supply  of  Seville.     Proc.  Inst.  C.  E.,  LXXVIII. 

P.  334- 

6.  Early  American    Pumping  and  Distributing  Plant.     Eng.  News,    1887, 

xvii.  p.  247. 

7.  The  Aqueduct  of  Zempola,  Mexico.     Eng.  News,  1888,  xx.  p.  2. 

8.  Manual  of  American  Water-works.      New  York,  1891. 

9.  Croes.      The  Water-works  of  Carthage.     Eng.  Record,  1891,  xxv.  p.  8. 

10.  Evolution  of  Water-supplies.      Eng.  Record,  1896,  xxxiv.  p.  162. 

11.  Lanciani.     The   Ruins   and    Excavations    of   Ancient    Rome.     Boston, 

1897. 

12.  Wegmann.     The  Water-works  of  Laodicea,  Asia  Minor.     Eng.  Record, 

1899,  XL.  p.  354. 

13.  Herschel.     Frontinus,   and  the  Water-supply  of  Rome.     Boston,  1899. 

A  translation  of  Frontinus,    with  many  valuable  comments  on  the 
water-supply  of  Rome. 

14     The  Center  Square  Water-works  of  Philadelphia;  the  Source  of  Water- 
supply  from  1801  to  1815.     Eng.  News,  1903,  XLIX.  p.  422. 

15.  Riggs.     The  Ancient  Water-tanks  of  Aden,  Arabia.     Eng.  News,  1904, 

LII.  p.  25. 

1 6.  Fisher.      London  Water-supply;    Old  and    New    Methods.      Westminster 

Rev.,  1905,  CLXIII.  p.  31. 

17.  Ancient  Water-supply  of  Athens.     Engr.,  1906,  ci.  p.  215. 


PART  I. 
REQUIREMENTS  AND  RESOURCES. 

A.    QUANTITY  OF  WATER  REQUIRED:  SOURCES  OF  SUPPLY. 


CHAPTER   II. 
QUANTITY   OF   WATER   REQUIRED. 

16.  Nature  of  the  Problem.  —  One  of  the  first  questions  to  be 
answered  when  a  new  or  enlarged  water-supply  is  under  consideration 
is  that  relating  to  the  quantity  which  will  be  required  when  the  works 
are  completed,  and  for  a  certain  period  in  the  future.  In  the  nature  of 
the  case  this  problem  can  be  solved  only  approximately.  Since  the 
total  quantity  consumed  is  sure  to  increase  in  the  future,  the  chief  effect 
of  an  error  in  the  estimate  will  be  to  vary  the  date  at  which  an  enlarge- 
ment of  the  capacity  will  be  required ;  but  even  so,  to  secure  the  most 
economical  construction  it  is  necessary  that  as  close  an  estimate  be 
made  as  possible. 

In  estimating  consumption  there  will  arise  two  cases: 

(1)  The  case  of  a  town  being  supplied  for  the  first  time; 

(2)  The  case  of  an  enlargement  of  an  old  supply. 

In  the  first  case  an  estimate  of  the  immediate  future  consumption 
must  be  made  by  a  study  of  the  consumption  of  towns  of  similar 
characteristics,  taking  into  consideration  the  various  modifying  influ- 
ences. In  the  second  case  the  consumption  is  already  known,  and  that 
for  a  few  years  in  the  future  can  be  readily  estimated.  In  both  cases, 
estimates  for  long  periods  ahead,  such  as  twenty  or  thirty  years,  are 
very  uncertain.  To  be  of  any  value  they  must  be  based  upon  a  careful 
study  of  the  circumstances  affecting  increase  in  population  and  the 
use  of  water. 

15 


1 6  QUA  NT  IT  Y  OF   WA  TER   REQ  UIRED . 

N 

Estimates  of  consumption  should  include  not  only  the  average 
quantity  which  will  be  required,  but  also  the  variation  in  the  consump- 
tion, in  order  that  the  various  parts  of  the  works — the  reservoirs, 
pumps,  and  distributing  system — may  be  properly  proportioned. 

17.  Consumption,  How  Stated. — Consumption  is  usually  stated  in 
terms  of  the  average  daily  consumption  per  capita  throughout  the  year 
on  the  basis  of  the  total  population  of  the  town  or  city.  In  large  cities 
the  total  population  corresponds  nearly  to  the  number  of  consumers, 
but  in  small  towns  ^  and  villages  only  a  small  percentage  of  the  inhabi- 
tants may  be  users,  and  the  statistics  for  such  places  are  of  little  value 
unless  the  number  of  takers  or  taps  is  also  given. 

The  amount  consumed  is  determined  in  various  ways.  Where 
pumps  are  used  it  is  obtained  by  multiplying  the  number  of  strokes 
made  by  the  pumps  by  the  displacement  of  the  plungers,  no  allowance 
ordinarily  being  made  for  slip.  The  resulting  error  will  not  usually 
exceed  2  or  3  per  cent,  and  is  not  of  great  consequence  in  this  connec- 
tion, but  occasionally,  as  in  the  case  of  leaky  suction-mains  or  well- 
tubes,  large  quantities  of  air  are  pumped  and  the  ' '  slip  ' '  becomes  very 
great.  In  gravity  works,  the  water  is  more  or  less  accurately  measured 
by  weirs,  or  by  the  known  capacity  of  certain  pipes  or  conduits,  or  is 
merely  guessed  at. 

In  whatever  way  determined,  the  total  amount  is  stated  as  the 
consumption.  It  therefore  includes  all  water  supplied,  whether  used, 
or  wasted,  or  lost  through  broken  pipes  or  mains.  Sometimes,  also,  it 
includes  water  used  in  the  condenser  of  the  pumping-engine  in  cases 
where  it  should  be  deducted. 

18.  Influences  Affecting  the  Consumption  per  Capita. — One  of  these 
influences  is  the  number  of  inhabitants  in  the  town  or  city.  This 
element  affects  the  per  capita  consumption  chiefly  by  affecting  the 
extent  to  which  use  is  made  of  private  sources  of  supply.  Thus  in 
large  cities  the  use  of  the  public  supply  is  almost  a  necessity,  while  in 
small  towns  and  villages  the  private  supplies  may  remain  in  use  to  a 
large  extent  long  after  the  introduction  of  the  public  supply. 

The  nature  of  the  industries  of  a  town  is  a  large  factor  in  determin- 
ing the  amount  of  water  used ;  also  the  wealth  and  habits  of  the  people, 
and  the  extent  to  which  water  is  used  for  fountains,  watering  of  lawns, 
street-sprinkling,  and  other  public  purposes.  Climate  has  also  a  very 
considerable  influence,  especially  as  to  the  amount  used  for  sprinkling 
purposes  and  that  which  is  wasted  in  winter  to  prevent  freezing.  It  is 
probable,  however,  that  the  most  important  factors  in  determining  the 
consumption  is  the  degree  of  care  taken  to  detect  leakage  or  waste, 


CONSUMPTION  FOR    VARIOUS  PURPOSES.  I/ 

and  the  fact  as  to  whether  the  water  is  sold  by  measure  or  otherwise. 
Good  quality,  abundant  quantity,  and  high  pressure  tend  to  increase 
the  consumption  by  encouraging  a  more  liberal  use  and  often,  at  the 
same  time,  greater  wastefulness. 

In  many  cases  the  introduction  of  a  new  or  an  improved  water- 
supply  is  followed  by  such  an  increase  in  consumption  that  the  time 
comes  sooner  than  expected  when  the  new  works  are  no  longer 
adequate  to  supply  the  demand.  When  estimating  the  probable  con- 
sumption under  the  second  case,  i.e.,  the  enlargement  of  an  old 
supply,  it  is  necessary  then  that  the  figures  relating  to  the  old  works 
be  used  with  considerable  caution.  Important  changes  in  the  character 
of  a  city  sometimes  also  occur,  and  with  small  towns  such  changes  may 
take  place  very  rapidly.  These,  however,  can  scarcely  be  predicted. 

19.  Consumption  of  Water  for  Various  Purposes. — In  order  to  make 
an  intelligent  application  of  data  pertaining  to  the  use  of  water,  some 
knowledge  is  desirable  of  the  consumption  for  various  purposes.     This 
information  is  especially  useful  in  the  design  of  works  for  places  of 
peculiar  characteristics,  in  the  design  of  the  different  parts  of  a  dis- 
tributing   system,    and    of    separate    supplies    for    different    purposes. 
Unfortunately  but  little  accurate  information  relating  to  the  consump- 
tion of  water  for  different  purposes  is  to  be  had,  as  the  use  of  meters 
for  all  consumers  is  of  rare  occurrence. 

The  different  uses  of  water  may  conveniently  be  divided  into  four 
general  classes:  (i)  Domestic  use;  (2)  Commercial  use;  (3)  Public 
use ;  (4)  Loss  and  waste. 

Probably  the  best  analysis  yet  made  of  the  subject  of  water-con- 
sumption for  different  purposes  is  that  by  Brackett,*  and  in  the 
following  discussion  his  paper  has  been  freely  drawn  upon ;  other  data 
are  taken  from  various  city  reports. 

20.  Domestic   Use. — The    following    table,   mainly  from    Brackett, 
gives  a  good  notion  of  the  actual  quantities  used  for  domestic  purposes 
and  the  variation  in  the  consumption  due  to  differences  in  the  character 
of  the  population.     The  figures  are  from  metered  supplies  and  represent 
what  may  be  considered  as  legitimate  consumption,  even  though  con- 
siderable water  may  have  been  wasted. 

The  consumption  per  capita  is  seen  to  vary  from  6.6  to  59  gallons 
per  day  for  the  lowest  and  highest  class  of  dwellings  respectively;  and 
the  average  for  a  town  varies  from  11.2  gallons  for  Fall  River,  a 
manufacturing  city,  to  44. 3  gallons  for  Brookline,  a  wealthy  suburb  of 

*  Trans.  Am.  Soc.  C.  E.,  1895,  xxxiv.  p.  185.  See  also  Jour.  New.  Eng.  W.  W. 
Assn.,  June,  1904,  p.  107. 


18 


QUANTITY  OF   WATER   REQUIRED. 


Boston.  From  these  data  it  would  appear  that  for  a  metered  supply 
the  domestic  use  may  easily  vary  from  1 5  to  40  gallons,  but  that  an 
allowance  of  20  to  30  gallons  would  in  most  cases  be  abundant. 

TABLE  No.  1. 

CON-SUMPTION    PER    CAPITA    FOR    DOMESTIC    PURPOSES    AS    DETERMINED    BY    METER 

MEASUREMENTS. 


City. 

Numberof 
Persons. 

Consump- 
tion per 
Capita  in 
Gallons. 

Remarks. 

Boston   Mass  

1,461 
8,432 
1,844 
1,699 
4,140 
2,450 
3,005 
170 
70,000 
90,942 
I87 
809 
8,183 

5,089 
34,ooo 
13,000 

59 
32 
16.6 
46.1 

44-3 
26.5 
6.6 
25-5 

II.  2 

16.8 
23-4 
15-6 
25-5 

18.6 

20.6 

21.3 

Highest-cost  apartment-houses  in  city. 
Moderate-class  apartment-houses. 
Poorest-class  apartment-houses. 
Boarding-houses. 
Average  of  all  dwellings  supplied  by  meter. 
All  houses  supplied  with  modern  plumbing. 
These  families  have  but  one  faucet  each. 
The  most  expensive  houses  in  the  city. 
Average  of  all. 
Whole  domestic  consumption. 
Cedar  Street,  best  class  of  houses. 
Austin  Street,  cheaper  houses. 
Houses  renting  from  $250  to  $600  each,  having 
bath  and  two  water-closets. 
Middle  class,  average  rental  $200. 
Average  of  all. 
Total  domestic  and  commercial  use. 

<  t           <  « 

•  «           « 

«           « 

Brookline,  Mass.. 
Newton,  Mass.  .  .  . 

Fall  River,  Mass.. 

Worcester,  Mass.  . 
«              >  i 
London,  Eng  

<  i             « 

Yonkers,  N.  Y.... 
Madison,  Wis  

With  an  unmetered  supply  the  domestic  consumption  and  waste 
may  be  many  times  greater  than  the  figures  given  above.  In  Boston 
the  estimated  actual  domestic  consumption,  including  waste,  was  in 
1892  (for  the  Cochituate  works)  62.24  gallons  per  capita  out  of  a 
total  of  94.93  gallons.  In  Philadelphia,  a  city  having  an  unmetered 
service,  meters  were  placed  experimentally  upon  the  services  of  twenty 
residences  in  different  parts  of  the  city.  The  consumption  for  four 
of  these  services  averaged  149  gallons  per  head  per  day,  the  highest 
rate  being  181  gallons.  In  several  other  cases  the  rate  averaged  from 
40  to  60  gallons,  while  in  some  it  was  as  low  as  9  gallons.  In  1893, 
142  houses  were  inspected  and  the  average  consumption  found  to  be 
222  gallons  per  capita. 

21.  Commercial  Use. — Under  this  head  are  included  all  uses  for 
mechanical,  trade,  and  manufacturing  purposes.  Large  users  of  water 
for  such  purposes  are  office  buildings  and  stores,  hotels,  factories, 
elevators,  railroads,  breweries,  sugar-refineries,  and  a  few  other  indus- 
tries. In  1892  the  consumption  in  Boston  for  various  commercial 
purposes  as  determined  mostly  by  meters  was  as  follows: 


CONSUMPTION  FOR    VARIOUS  PURPOSES. 


Office-buildings  and  stores,  gals,  per  head  for  total  population 11.17 


Steam-railroads, 

Sugar-refineries, 

Factories, 

Breweries, 

Steamers  and  shipping, 

Elevators  and  motors, 

Saloons, 

Hotels, 

Miscellaneous, 


Total 


2.26 
1.70 
2.15 
0.89 
0.90 

2-95 
1.16 
1.62 
5-47 

30.27 


Similar  statistics  for  1880  indicated  a  consumption  of  about  25 
gallons  per  capita.  At  Syracuse,  N.  Y.,  in  1888-89,  7-2  gallons  per 
capita  were  used  in  operating  elevators  and  23.2  gallons  for  other  com- 
mercial purposes.  In  New  York  City  the  consumption  for  commercial 
purposes  is  about  24  gallons  per  capita.  Mr.  Brackett  considers  that 
35  gallons  per  capita  should  be  allowed  in  making  provision  for  the 
future  supply  of  Boston. 

In  smaller  cities  the  consumption  for  commercial  purposes  would 
in  many  cases  be  much  less,  while  in  some  it  might  be  more.  In 
Fall  River,  for  example,  in  1892  the  commercial  consumption  was 
estimated  at  2  gallons  per  capita,  this  low  value  being  due  to  the  fact 
that  most  of  the  factories  at  that  place  get  their  supply  directly  from 
the  river.  In  Yonkers,  N.  Y. ,  a  fully  metered  town  (population 
34,000),  the  consumption  for  commercial  purposes  was,  in  1897,  27.4 
gallons  per  capita,  the  total  being  1 02  gallons.  Considering  the 
above  data,  it  is  probably  fair  to  estimate  the  consumption  for  com- 
mercial purposes  at  from  5  to  35  gallons  per  capita  according  to  the 
nature  of  the  town. 

22.  Public  Use. — This  includes  the  water  used  for  schools  and 
other  public  buildings,  street-sprinkling,  water-troughs  and  fountains, 
sewer-flushing  and  the  flushing  of  water-mains,  fire-extinguishment, 
and  a  few  other  occasional  uses.  Water  for  such  purposes  is  seldom 
measured,  but  the  amount  is  not  likely  to  exceed  on  the  average  a  few 
gallons  per  capita,  although  the  rate  of  consumption  is  far  from  being 
uniform.  In  the  following  table  is  given  the  consumption  for  various 
public  purposes  in  Boston  for  1892,  and  in  Fall  River  for  1899,  the 
water  being  in  both  cases  partly  metered  and  partly  estimated. 

Fall  River. 

1.36          , 

1.02 

.48 

I.QI 

.II 

•  33 
.36 


Boston. 
Public  buildings,  schools,  etc.,  gals,  per  capita 2.30 


Street-sprinkling, 

Sewer-flushing, 

Water-troughs  and  fountains, 

Fires, 

Blowing  off  dead  ends, 

Miscellaneous, 


1. 00 
.10 

.25 

.10 


Total, 


3-75 


5-57 


2O  .        QUANTITY  OF   WATER  REQUIRED. 

In  many  places  much  more  water  is  used  for  sprinkling  purposes 
than  the  quantities  given  above.  Estimates  for  a  few  places  are  as 
follows:  In  Minneapolis,  in  1897,  5  gallons  per  capita;  in  Indianapolis, 

3  gallons;   Rochester,  N.    Y.,    3  gallons;   Newton,   Mass.,  4  gallons; 
Madison,  Wis.,   10  gallons.*    Street-sprinkling  is  carried  on  for  about 
half  the  year  only,   so  that  the  actual  rate  of  consumption  is   about 
double  these  figures.      Lawn-sprinkling  in  public  parks  would  add  very 
little.      Assuming  an  amount  for  this  purpose  equal  to  Ta¥  inch  in  depth 
per  day,  and  allowing  10  acres  for  each  25,000  inhabitants,  the  average 
used  would  be  equal  to  about  I  gallon  per  head  per  day  for  the  period 
of  two  or  three  dry  months. 

For  fire  purposes  the  average  consumption  is  very  small,  but  at 
times  the  rate  is  very  high.  (See  Art.  32.) 

Few  American  cities  use  any  considerable  quantity  of  water  for 
ornamental  purposes,  and  it  might  be  well  to  consider  whether  a  part 
of  the  large  amounts  wasted  in  some  of  our  cities  might  not  be  more 
advantageously  used  in  adding  to  the  attractiveness  of  public  parks  and 
squares  by  means  of  ornamental  and  drinking  fountains.  The  amount 
of  water  used  in  some  of  the  ornamental  fountains  in  the  European 
capitals  is  at  times  very  large,  but  does  not  add  greatly  to  the  average 
consumption.  In  Paris  the  average  is  estimated  at  only  about  2.4 
gallons  per  capita  daily,  although  there  are  many  fountains  using  from 

4  to   loo  gallons  per  second.     These,  however,  are  allowed  to  play 
only  at  certain  hours  or  on  special  occasions. 

The  total  consumption  for  public  purposes  may  finally  be  estimated 
at  from  3  to  10  gallons  per  head,  averaging  perhaps  5  gallons,  the 
amount  depending  largely  on  the  item  of  street-sprinkling. 

23.  Loss  and  Waste. — The  enormous  quantities  of  water  (150  to 
300  gallons  per  head  per  day)  used  by  some  of  the  large  cities  of  the 
United  States,  when  compared  with  the  foregoing  data  from  metered 
supplies,  indicate  that  a  very  large  percentage  of  the  water  furnished  is 
lost  through  leakage  or  is  wasted  by  the  consumer.  The  chief  causes 
of  such  waste  are  bad  plumbing,  leaky  mains,  waste  to  prevent  freez- 
ing, and  willful  or  careless  waste.  The  waste  by  the  domestic  con- 
sumer has  already  been  considered  under  domestic  consumption.  With 
metered  supplies,  water  may  still  be  badly  wasted  by  the  consumer, 
but  such  being  paid  for  at  regular  rates,  it  must  be  considered  as  legiti- 
mate consumption.  But  when  all  services  are  metered  and  a  liberal 
allowance  is  made  for  public  uses,  there  is  still  a  large  amount  of  water 
apparently  furnished  which  is  not  accounted  for. 

This-  discrepancy  or  loss  is  due  to  three  causes:  errors  in  meters, 

*  Boston  Met.  Dist.,  1901,  2.13  gal.  See  table  in  Jour.  New.  Eng.  W.  W.  Assn., 
June  1904,  p.  126. 


CONSUMPTION  FOR    VARIOUS  PURPOSES. 


21 


This  discrepancy  or  loss  is  due  to  three  causes  :  errors  in  meters, 
errors  in  estimating  the  pumpage  due  to  the  slip  of  the  pumps,  and 
actual  loss  through  leaks  and  breakages.  Meters,  when  old,  will  tend 
to  register  less  than  the  true  amount,  especially  when  measuring  small 
quantities ;  furthermore,  the  actual  amount  pumped  is  nearly  always 
less  than  that  figured  from  plunger  displacement,  and  to  correct  this, 
error  an  insufficient  allowance,  or  no  allowance  at  all,  may  be  made. 
Both  these  errors  act  to  increase  the  apparent  loss.  Probably  their 
combined  effect  will  rarely  be  less  than  5  per  cent  of  the  total  amount 
pumped,  and  may  easily  reach  10  per  cent.  The  actual  loss  is,  there- 
fore, often  considerably  less  than  the  apparent  loss. 

In  the  following  table  *  are  given  data  showing  the  amount  of  water 
unaccounted  for  in  certain  cities  where  all  or  nearly  all  water  used  is 
metered.  The  use  for  public  purposes  has  been  taken  into  account 
so  that  the  amount  unaccounted  for  represents  closely  the  leakage  and 
errors  of  measurement. 

The  towns  of  Milton  and  Belmont,  Mass.,  belong  to  the  Boston 
Metropolitan  district,  and  receive  their  water  through  Venturi  meters. 
All  consumers  are  also  metered.  The  water  unaccounted  for  amounts 
in  these  places  to  from  2000  to  5000  gallons  per  mile  of  pipe. 


Unaccounted  for. 

Total 

Popula- 

Consump- 

of 

City  or  Town. 

tion 
1900. 

tion  Gal- 
lons per 
Consumer. 

Taps 
Metered. 

Per  cent. 

Gallons 
per 
Consumer. 

Gallons 
per  Day 
per  Mile 

of  Pipe. 

\Vare,  Miass  

8,263 

44  o 

IOO    O 

30  8 

17    ^ 

1  1  2OO 

Wellesley,  Mass  

^,072 

SO.O 

IOO.O 

41  .  s 

2O  8 

3,4CO 

Yonkers,  N.  Y  

47,0-20 

80.0 

IOO.O 

4O.  7 

4^  •  7 

23,340 

Fall  River,  Mass  

104,860 

40-5 

96.0 

21.5 

8-5 

IO,OOO 

\Vorcester,  M!ass. 

1  18  4.20 

68  o 

04.    ^ 

46  c 

3i  6 

2O  8oO 

Brockton,  Miass.     .    .    . 

4.0,063 

•?6  o 

QO    O 

I?  8 

12    2 

6  200 

Woonsocket,  R.  I.     ... 

28,204 

28.6 

86.7 

23.0 

6.6 

4,37«> 

24.  Leakage  from  mains  has  been  directly  determined  in  several 
cases.  Tests  of  comparatively  new  pipe  systems  indicate  a  leakage  of 
from  500  to  1 200  gallons  per  day  per  mile,  and  one  engineer  specifies 
a  maximum  allowable  leakage  of  60  to  80  gallons  per  mile  per  inch 
of  diameter  of  pipe.f  Certain  tests  of  pipes  in  several  German  and 
Dutch  cities  showed  leakages  of  less  than  300  gallons  per  mile.J  A 

*  Jour.  New  Eng.  W.  W.  Assn.,  June,  1904,  p.  132. 
t  Trans.  Am.  Soc.  C.  E.,  1897,  xxxvin.  p.  30. 
$  Jour.f.  Gasbel.  u.   Wasservers.,  1894,  p.  722. 

0621 


'  22 


QUANTITY  OF   WATER  REQUIRED, 


test  of  a  24-inch  main  by  Mr.  Brush  *  showed  a  leakage  of  6400  gal- 
lons per  day  per  mile,  under  a  pressure  of  no  pounds  per  square  inch. 
In  large  systems,  cases  of  breakages  of  4-  and  6-inch  mains  have 
occurred  which  have  remained  long  undiscovered,  the  water  flowing 
away  through  adjacent  sewers  at  rates  as  high  as  100,000  gallons  per 
24  hours.  In  1902  the  amount  supplied  to  Stoneham,  Mass.,  was  re- 
duced from  800,000  gallons  per  day  to  330,000  gallons  by  the  repair  of 
four  large  leaks  in  the  street  mains,  which  had  been  discovered  by 
special  investigation.  During  the  same  year  eight  leaks  in  the  Boston 
works  were  found  to  be  wasting  about  650,000  gallons  per  day. 

Pipe-leakage  is  likely  to  increase  as  the  system  gets  older,  on 
account  of  the  loosening  of  joints  through  settlement,  increased  leakage 
of  valves,  etc.  As  a  general  estimate  Mr.  Kuichling  f  uses  the  values 
of  2500  to  3006  gallons  per  mile  of  pipe.  This  is  equivalent  to  from 
3  to  10  gallons  per  capita,  the  population  per  mile  of  pipe  usually 
ranging  from  about  300  to  1000. 

Considering  these  various  facts,  the  total  amount  of  water  lost  or 
unaccounted  for  in  metered  supplies  may  be  placed  at  from  15  to  30 
gallons  per  capita. 

25.  Total  Consumption  per  Capita.  —  Recapitulating  the  above  esti- 
mates for  various  purposes,  we  have,  as  reasonable  extreme  and  average 
values  for  those  supplies  having  a  fairly  good  meter  system  : 


Use.- 

Gallons  per  Capita. 
Daily. 

Minimum. 

Maximum. 

Average. 

Domestic             

15 

5 
3 
IS 

40 
35 

10 

30 

25 
20 

5 
25 

Commercial     .    .  '.    .    . 

Public  

Loss 

Total    

38 

"5 

75 

As  it  will  seldom  occur  that  for  any  given  place  the  conditions  are  all 
favorable  for  a  minimum  or  a  maximum  use  for  all  purposes,  the  above 
totals  are  to  be  considered  as  much  more  extreme  figures  than  the 
separate  items. 

For  the  Boston  Metropolitan  district  the  result  of  a  careful  analysis 
of  data  by  Brackett  places  these  figures  as  follows :  Domestic,  25  gal- 

*  Trans.  Am.  Soc.  C.  E.,  1888,  IX.  p.  89. 

f  Trans.  Am.  Soc.  C.  E.,  1897,  xxxvm.  p.  19. 


CONSUMPTION  FOR    VARIOUS  PURPOSES.  2$ 

Ions;   commercial,  23.5    gallons;  public,    7    gallons;  loss   and    waste, 
about  65  gallons.* 

TABLE    NO.    2. 

CONSUMPTION   OF    WATER   IN    AMERICAN    CITIES   AND   TOWNS   IN    1890  AND    1905. 


City. 

Population. 
1900. 

Popula- 
tion per 
Tap. 
1890. 

Per  cent 
of  Taps 
Metered. 
1890. 

Consump- 
tion per 
Inhabitant 
Daily. 
1890. 

Per  cent 
of  Taps 
Metered. 
1905- 

Consump- 
tion per 
Inhabitant 
Daily. 
1905- 

Chicago         

1,  608  600 

7    I 

2     ? 

I4O 

Philadelphia     .... 
St.  Louis  

1,293,700 

^7^,  2OO 

6.1 
ii  8 

o-3 

8    2 

132 

72 

I.O 

7   o 

230 
Q2 

Boston 

t?6o  900 

6  6 

r    n 

80 

r   o 

Cleveland 

08  1  800 

8    7 

is 

IO3 

o  •  w 
68 

•"•D1 

Buffalo 

?C2  4OO 

6  * 

0  •" 

O    2 

186 

L6I 

San  Francisco  .... 
Cincinnati  

342,800 
•22  ?,QOO 

9  •  9 

41.4 
41 

61 

112 

21 
12 

3^4 
96 
I  3O 

Detroit  

28?,7OO 

'  O 
C     I 

2    I 

161 

Q 

1  88 

Milwaukee    

28?,?OO 

II    I 

•21     Q 

I  IO 

80 

O  j 

Louisville 

2O4  72O 

II    O 

5Q 

74 

8 

81 

Minneapolis      .... 
Providence    .    . 

202,720 
1  7  r  600 

I6.5 

9       A 

6-3 

62    4 

75 
48 

47 
86 

76 
68 

Indianapolis      .... 
Kansas  City     .... 
St.  Paul     

169,160 
163,750 
162,06^ 

35-6 

12    7 

7.6 

4.  2 

7i 
60 

10 

38 

38 

82 

73 
s6 

Rochester  

162,600 

<  .4 

II  .4 

66 

41 

88 

Toledo 

1  31  820 

18  6 

9       A 

72 

7O 

7e 

Columbus,  O  
Worcester,  Mass.     .    . 
Fall  River,  Mass.     .    . 
Memphis,  Tenn.      .    . 
Lowell,  Mass  
Atlanta,  Ga  

125,560 
118,420 
104,860 
102,320 
94,970 
80,870 

u-5 
8.9 
14.9 
xi.  9 

9.2 
20.  o 

6.4 
89.4 
74-6 

3-7 
22.9 
89.6 

78 

59 
29 
124 
66 
36 

76 

95 
97 

20 
69 
IOO 

ij 
110    , 

75 
42 

IOO 

58 
6< 

Dayton,  Ohio  .... 
Nashville,  Tenn.      .    . 
Camden,  N  J.     ... 
Yonkers,  N.  Y.     ... 
Newton,  Mass.     .    .    . 
Aurora,  111. 

85,333 
80,870 

75>94o 
47,93° 
33,587 

24  14.7 

20.0 
14-9 

12.0 

i:ft 

3-8 
o  8 

s2:4 

67.4 

IO    3 

47 
146 

131 
68 
40 

4O    7 

70 

52 
3 

36  t 

70 
148 
i55 
"5 
58 
c6t 

Madison,  Wis.      .    .    . 
Ashland,  Wis  
Champaign    &  Urbana, 
111. 

19,164 
13,074 

14  826 

II  .0 

9-9t 
7  of 

31.0 

2.8 
2    ^ 

40 
90 

4*t 

ow-  1 
97 

A 

46 

81 

A? 

Chippewa  Falls,  Wis. 
Middleborough,  Mass. 
Beloit,  Wis  

8,094 
6,885 
10,436 

7-6] 
7-4T 

11.7 

IO    2f 

6.6 

24.0 
10  ot 

to  \ 
13-8 
21 
64  1 

47 

+5 

IOO 

38 

I  30 

Foxbo  rough,  Mass. 
Clinton,  111. 

3,266 

44^2 

8.7 
4    it 

34-o 

•2     O 

44-0 

27    o 

46 
i  it 

63 

oot* 

Shenandoah,  la.  .    .    . 
Melrose,  Mass.     .    .    . 

3,573 
12,962 

15-  st 

4.2 

.':> 

i-7t 

'; 

39t 
7if 

3 

35 

112 

26.  In  Table  No  2  are  given  data  concerning  consumption  and  the 
use  of  meters  in  various  cities  for  1890  and  1905,  complied  mainly  from 
the  Manual  of  American  Water-works  for  1890,  and  from  a  paper  by 

*  Jour.  New  Eng.  W.  W.  Assn.,  June,  1904,  p.  127. 
t  1895. 


24  QUANTITY  OF   WATER  REQUIRED. 

Bailey  containing  statistics  for  136  large  cities.*  The  very  considerable 
increase  in  consumption  in  nearly  every  city  during  the  period  from 
1890  to  1905  is  noteworthy.  In  some  cases  this  increase  is  evidently 
much  beyond  any  legitimate  increase  in  demand.  The  great  increase  in 
the  use  of  meters  is  also  noteworthy. 

For  cities  above  25,000  inhabitants  the  size  has  no  apparent  relation 
to  the  consumption.  This  fact  is  more  clearly  shown  by  the  average 
consumption  for  groups  of  cities  of  different  size.  Mr.  Kuichlingf 
finds  for  100  of  the  largest  cities  in  the  United  States  and  Canada  the 
following  averages  for  1895  : 

For  Cities  of  a  Population  of  Consumption  per  Capita. 

1,000,000  and  more 106  gallons. 

600,000  to  300,000 122         " 

300,000  to  100,000 106         " 

100,000  to    50,000 105         " 

50,000  to    30,000      .    .    . 105         " 

The  large  value  for  the  second  group  is  due  to  the  high  consumption  of 
220  gallons  for  Pittsburg.  For  towns  smaller  than  the  above  the  consump- 
tion is  generally  lower,  partly  on  account  of  a  less  commercial  use  and 
partly  because  the  water  is  used  by  only  a  portion  of  the  community. 

In  a  general  way  the  effect  upon  consumption  of  the  ratio  of  popu- 
lation to  taps  is  observable  for  the  various  cities,  but  too  many  other 
elements  enter  to  enable  any  definite  relation  to  be  traced.  The  great 
irregularity  in  consumption  among  the  large  cities,  and  the  enormous 
quantities  used  by  some,  can  be  explained  only  on  the  supposition  that 
a  large  part  of  the  water  is  wasted  and  lost.  The  effectiveness  of 
meters  in  preventing  very  high  rates  of  consumption  is  clearly  brought 
out  by  the  table  ;  for  with  two  exceptions,  no  city  having  20  per  cent  of 
its  taps  metered  has  a  consumption  appreciably  above  100  gallons. 

From  statistics  of  the  consumption  for  1900  in  136  cities  having  a 
population  exceeding  25,000  the  relation  of  consumption  to  meters  is 
roughly  given  by  the  following  averages  :  \ 

Per  cent  of  Taps  Average  Consumption. 

Metered.  .  Gallons  per  capita. 

Less  than  10 153 

10  to  25 no 

25  to  50 104 

More  than  50 62 

27.  Increase  in  Consumption. —  For  many  years  past  there  has  been 
a  large  and  steady  increase  in  the  consumption  of  water.  This  is  due 
chiefly  to  the  more  general  use  of  water  and  to  an  increase  in  the 

*  Eng.  News,  1901,  XLV.  p.  279. 

t  Trans.  Assn.  C.  E.  of  Cornell  University,  1898,  p.  10. 

J  Eng.  News,  1901,  XLV.  p.  279. 


INCREASE  IN  CONSUMPTION. 


number  of  fixtures  in  the  houses  supplied  ;  but  where  no  restriction  has 
been  imposed  upon  the  use  of  water  the  waste  has  increased  even  faster 
than  the  legitimate  use,  so  that  in  many  cases  the  consumption  has 
become  enormously  high. 

To  exhibit  the  general  tendency  the  consumptions  per  capita  for 
several  large  cities  for  the  period  from  1875  to  1900-05  have  been 
plotted  in  Fig.  3.  The  curves  for  the  cities  of  Chicago  and  Philadelphia 


A^ 


#00      'OS    /875 


209 


J50 


'90 


/900 


FIG.   3.  —  VARIATION  IN  YEARLY  RATES  OF  CONSUMPTION. 

show  in  what  manner  the  unrestricted  use  of  water  is  likely  to  raise  the 
consumption.  Omitting  such  cases  of  excessive  rates  of  increase,  there 
still  remains  a  marked  tendency  towards  an  increased  consumption  of 
water.  With  originally  low  rates  of  consumption  this  increase  is  large 
even  with  well-metered  cities,  such  as  Providence,  for  example,  with  82 
per  cent  metered.  This  is  also  well  shown  in  the  figures  of  Table  No.  2. 
Of  the  ten  largest  cities  having  over  50  per  cent  of  taps  metered  in 
1905,  all  but  three  showed  a  considerable  increase  in  consumption,  the 
average  rate  for  these  cities  increasing  from  65  gallons  in  1890  to  78 
gallons  in  1905.  The  city  of  Milwaukee  (Fig.  3)  is  a  good  example  of 
the  restraining  effect  of  meters  in  a  large  city.  About  80  per  cent  of 
the  taps  were  metered  in  1905. 

Some  of  the  cities,  such  as  Boston  and  St.  Louis,  have  good  systems 
of  inspection,  and  the  consumption,  though  not  excessive,  is  yet 
increasing  at  quite  a  high  rate. 


26  QUANTITY   OF  WATER  REQUIRED. 

It  would  therefore  appear  that  even  with  the  best  systems  the  per- 
capita  consumption  of  water  is  likely  to  continue  to  increase  for  some 
time  to  come.  In  case  the  use  of  water  is  already  restricted,  it  would 
not  in  general  be  safe  to  estimate  the  amount  of  this  increase  at  less 
than  10  or  15  gallons  for  the  next  decade.  Where  few  meters  are  used 
at  present,  the  consumption  could  in  many  cases  be  greatly  reduced  by 
their  introduction,  or  by  a  better  inspection  system. 

The  difficulty  of  estimating  future  consumption  is  illustrated  by  the 
case  of  Boston.  In  the  investigation  for  the  Metropolitan  district, 
made  in  1894,  it  was  estimated  that  100  gallons  per  capita  would  be 
sufficient  for  thirty  years  to  come.  As  a  matter  of  fact  the  consumption 
in  the  district  increased  from  83  gallons  in  1893  to  129  gallons  in  1905. 

28.  Variations  in  Consumption. — The  foregoing  articles  have  dis- 
cussed only  the  average  consumption  throughout  the  year.     There  will 
now  be  considered  the  variations  which  occur  in  the  consumption  from 
time  to  time. 

For  the  design  of  the  different  parts  of  the  works  it  is  desirable  to 
know  the  monthly,  the  daily,  and  the  hourly  variations.  The  varia- 
tions for  periods  of  one  month  or  more  are  of  use  in  questions  pertaining 
to  large  storage-reservoirs,  while  those  for  short  periods  of  a  few  days 
or  hours  are  of  use  in  the  design  of  pumps,  service-reservoirs,  and 
mains.  For  example,  if  no  storage  exists  between  the  pumps  and  the 
consumer,  then  the  pumps  must  be  designed  to  furnish  water  at  the 
maximum  possible  rate  of  consumption,  while  with  a  certain  amount  of 
storage  they  may  be  designed  with  only  sufficient  capacity  to  supply 
water  at  the  maximum  daily  rate  or  at  the  maximum  weekly  rate. 
Likewise  with  no  storage  the  source  of  supply,  whether  surface-water 
or  ground-water,  must  have  a  capacity  sufficient  at  all  times  to  supply 
water  at  the  maximum  rate.  With  more  or  less  storage  the  capacity 
of  the  source  can  be  more  or  less  reduced. 

29.  Monthly  Variations. — In  nearly  all  cases  the  rate  of  consump- 
tion reaches  a  maximum  in  the  summer  owing  to  the  use  of  water  for 
street-  and  lawn-sprinkling.     This  high  rate  usually  extends  over  two 
or  three  months.     A  secondary  maximum  often  occurs  in  the  winter, 
due  to  the  waste  of  water  to  prevent  freezing,  but  the  use  of  meters 
will  largely  prevent  excessive  variations  from  this  cause.     In  extreme 
cases,    however,    the   winter    consumption    may   be   very   high.      For 
example,    during    the    severe    winter    of    1898-99    service-pipes    quite 
generally  froze  in  many  places  in  the  Northwestern  States,  and  in  some 
of  these  towns  the  waste  of  water  to  prevent  further  freezing  raised  the 
daily  consumption  to   300  or  400  gallons  per  capita  for  several  weeks. 


VARIATIONS  IN   CONSUMPTION. 


The  occurrence  of  a  large  fire  at  such  a  time  would  be  likely  to  prove 
disastrous.  Such  a  contingency  should,  however,  be  met  by  using  a 
more  ample  margin  of  safety  in  the  depth  at  which  the  pipes  are  laid, 
and  need  only  be  considered  to  a  slight  extent  as  a  possible  element 
in  causing  high  consumption. 

The  monthly  variations  in  consumption  for  several  places  are  illus- 
trated by  the  curves  of  Fig.  4 ;  and  further  data  relating  to  monthly 
rates  are  given  in  Tables  No.  3  and  3a. 


/so 
no 
/oo 

so 

60 


no 

100 
90 
60 

ISO 

tio 

100 
50 
60 


fall  - 


I  I 


.  df. 


FIG.  4. — RATIOS  OF  MONTHLY  TO  AVERAGE  CONSUMPTION. 

From  the  diagrams  and  table  it  may  be  concluded  that  the  maxi- 
mum monthly  rate  will  seldom  exceed  125  per  cent  of  the  average, 
it  being  in  fact  much  below  this  figure  for  most  places  represented. 
The  diagram  further  shows  that  excessive  consumption  is  likely  to  con- 
tinue for  two  or  three  consecutive  months,  averaging  for  this  longer 
period  a  rate  of  1 10  to  115  per  cent  of  the  yearly  average. 

30.  Daily  Variations. — The  maximum  daily  rate  is  usually  esti- 
mated at  about  150  per  cent  of  the  average.  In  the  tables  very  con- 
siderable differences  are  to  be  noted  in  the  ratios  for  different  places, 
these  being  caused  by  a  variety  of  conditions,  some  accidental  and 


28 


QUANTITY  OF   WATER   REQUIRED. 


TABLE    NO.    3. 

MAXIMUM   MONTHLY  AND   DAILY   RATIOS   EXPRESSED   AS   PERCENTAGES   OF   AVERAGE 

CONSUMPTION. 


Ratio  of 

Ratio  of 

Ratio  of 

Ratio  of 

Maximum 

Maximum 

Maximum 

Maximum 

City. 

Monthly  to 

Daily  to 

City. 

Monthly  to 

Daily  to 

Average 

Average 

Average 

Average 

Consumption 

Consumption. 

Consumption. 

Consumption. 

Chicago  .    .    . 

1  08 

116 

Louisville  .    .    . 

127 

135 

Philadelphia   . 

no 

122 

Columbus      .    . 

107 

157 

Boston.    .    .    . 

114 

119 

Fall  River.    .    . 

115 

Cincinnati   .    . 

124 

*53 

Dayton  .... 

118 

;7s 

Cleveland    .    . 

114 

146 

Newton      .    .    . 

125 

143 

Buffalo     .    .    . 

1  68 

Pawtucket     .    . 

in 

153 

Detroit     .    .    . 

117  . 

I5° 

Woonsocket,R.I. 

122 

155 

Milwaukee  .    . 

H3 

Marquette,  Mich. 

139 

194 

TABLE    NO.    3A.* 

MAXIMUM    MONTHLY,    WEEKLY   AND    DAILY   RATIOS    FOR    MASSACHUSETTS   CITIES,    EXPRESSED 

AS    PERCENTAGES. 
A  verages  for  Six   Years, 


City  or  Town. 

Population, 
1900. 

Average 
Daily 
Consumption, 
per  Capita, 
Gallons. 

Percentages  of  Maximum 
to  Average  Consumption. 

Monthly. 

Weekly. 

Daily. 

Worcester  (less  than  6  years)  . 
Fall  River  

118,421 
104,863 
94,969 
91,886 

73,597 
62,559 
62,442 
40,063 
35,956 
3i,036 
26,121 
23,481 

19,935 
19,822 

15,487 
14,478 

14,254 
13,884 
13,609 
13,463 
11,523 
n,335 
11,302 
10,813 
9,816 

58 
36 

79 
81 

67 

55 
96 

3° 
67 
46 
32 
76 
85 
42 
53 
4i 
73 
70 

37 
61 
89 
36 

£ 

62 

39 

117 

121 
117 
H3 

116 

III 
"3 
134 
114 

116 
129 

H5 
124 
146 
124 
114 
123 
140 
119 

121 
114 
I30 
122 
125 
138 

128 

130 
130 
138 
125 

*34 
126 

164 
119 
127 
142 

135 
1  60 

147 
127 
128 
145 
163 
119 

136 
127 
i54 
i43 
128 
167 

165 
15° 

!50 

1  80 
177 

164 

151 
232 
178 

147 
i93 

1  88 

184 
1  66 
i8a 

i57 
218 

222 
220 
158 
155 

245 
194 
169 

233. 

Lowell    

Cambridge    

Lynn  and  Saugus    

Lawrence  

New  Bedford    .    . 

Brockton   

Salem     .    . 

Taunton    

Gloucester 

Waltham  (5  years  only).    .    . 
Brookline 

Hyde  Park  and  Milton  .    .    . 
Wakefield  and  Stoneham  .    . 
Newburyport    

Woburn 

Beverly  .... 

Marl  borough    

Milford  and  Hopedale    .    .    . 
Peabody 

Attleborough 

Framingham 

Gardner    .... 

Abington  and  Rockland     .    . 

*  From  Mass.  Bd.  Health  Report,  1900,    p.  613. 


VARIATIONS  IN   CONSUMPTION.  29 

some  constant.  For  the  larger  cities  the  ratio  of  150  per  cent  appears 
to  be  a  fair  maximum,  but  for  the  smaller  cities  the  ratio  is  frequently 
over  200  per  cent.  Generally  speaking,  the  lower  the  average  consump- 
tion the  greater  the  variation.  The  maximum  daily  rate  will  usually 
occur  in  the  month  of  maximum  consumption,  and  a  rate  considerably 
above  the  average  for  the  month  will  obtain  for  several  consecutive 
days.  Thus  where  the  maximum  daily  consumption  is  150  per  cent  of 
the  average,  the  maximum  weekly  consumption  is  likely  to  be  about 
130  per  cent  of  the  average,  but  for  longer  periods  of  time  the  rate 
will  approach  the  monthly  maximum. 

31.  Ordinary  Hourly  Variations.  —  If  there  were  no  waste  or  leak- 
age, the  consumption  during  several  hours  of  the  night  would  be  almost 
nothing  and  the  relative  variations  in  consumption  throughout  the  24 
hours  would  be  very  great.  Whatever  leakage  exists  is  nearly  constant 
and  tends  therefore  to  decrease  these  variations.  During  the  summer, 
when  the  monthly  rate  is  high,  the  hourly  rate  is  also  likely  to  be  high, 
as  the  excessive  use  of  water  at  that  time  of  the  year  is  largely  due  to 
lawn-  and  street-sprinkling,  which  usually  occurs  at  a  time  of  day  when 
the  consumption  for  other  purposes  is  large.  This  results  in  a  very 
high  hourly  rate.  To  prevent  this  excessive  rate  many  towns  have 
regulations  requiring  the  sprinkling  of  lawns  to  be  done  at  special  hours 
when  the  demand  for  other  purposes  is  somewhat  lessened.  The  con- 
sumption in  the  winter,  although  it  may  be  great,  is  more  uniform 
throughout  the  24  hours,  as  the  waste  at  this  time  of  year  will  be  the 
greatest  at  night.  In  small  cities  the  demand  is  likely  to  be  more 
irregular  than  in  large  cities. 

Measurements  made  in  Boston  in  August,  1893,  gave,  for  the 
Mystic  works,  the  following  rates  of  consumption  for  different  portions 
of  the  day,  expressed  as  gallons  per  head  per  day. 

i  to  4  A.M 40.8  gallons  i  to  4  P.M 98.2  gallons 

4  to  7    "    58.6     "  4  to  7    "       79.5       « 

7  to  10  "    103.8     "  7  to  10  "       61.9       «* 

10  A.M.  to  I  P.M.  .  .    93.0  "  10    P.M.  to  I  A.M 52.9         «« 

Average 73.6  gallons 

The  maximum  rate  for  3  hours  was  thus  103.8  gallons,  or  141  per  cent 
of  the  average;  and  from  7  A.M.  to  7  P.M.  the  rate  was  127  per  cent 
of  the  average  for  the  day.  Referring  to  Table  No.  3  and  assuming 
the  variation  on  the  day  of  greatest  draught  to  be  the  same  as  here 
given,  the  maximum  draught  from  7  to  10  A.M.  for  the  year  would 
then  be  141  per  cent  of  119  per  cent  =  168  per  cent  of  the  daily 
average  for  the  year.  The  large  consumption  from  I  to  4  A.M.  must 
have  been  mostly  waste. 


QUANTITY  OF   WATER  REQUIRED. 


In  Detroit  the  maximum  hourly  demand  in  1894  and  in  1895  was 
1 78  per  cent  of  the  average  yearly  rate. 

Mr.  Coffin  found  for  Attleboro,  Mass,  (population  7577  in  1890), 
a  rate  for  the  maximum  month  of  122  per  cent  of  the  average  yearly 
rate,  maximum  week  134  per  cent,  maximum  day  155  per  cent,  maxi- 
mum hour  of  maximum  day  333  per  cent,  maximum  two  continuous 
hours  312  per  cent,  and  minimum  hour  45  per  cent.  The  average  rate 
AM  RM  AM  p.  M 

^   ?   4-    6    8    /O  /?  £  4-    6    G    /O  /?  2  4-    fi   8    /O  /2  2    4-    6   fi 


60t 


~>c  fe  57< '/ 


3/.Kfa 


TVC 
t.  1 1 


A* 


fin 


A 


V2  ~<?  ~4    66  X?  J2  £   46  6   /O  /£  £   4    6  8   P  /£  £  -?   6  &    '0  & 
A  M:  B  M.  AM-  P.  M. 

FIG.  5.  —  HOURLY  VARIATIONS  IN  CONSUMPTION. 

from  10  A.M.  to  3  P.M.  for  three  days  in  the  month  of  maximum   con- 
sumption  was  230  per  cent  of  the  average.* 

In  Fig.  5  are  plotted,  for  two  days  each,  the  hourly  rates  of  con- 
sumption, expressed  as  percentages  of  the  average  hourly  rate  for  the 
entire  day,  for  the  cities  of  New  York  City,f  Rochester, J  N.  Y., 
Binghamton,^  N.  Y.,  Des  Moines,§  la.,  Rockford,||  111.,  and  Rock 
Island,^]"  111.  For  the  city  of  Rockford  the  high  consumption  during 
sprinkling  hours,  6  to  8  P.M.,  is  notable,  and  for  all  places  the  large 
consumption  during  the  night.  The  total  per-capita  consumption  of 
these  places  was  for  1895  approximately  as  follows:  New  York  City, 
100  gallons;  Rochester,  71  gallons;  Binghamton,  135  gallons;  Des 

*  Trans.  Am.  Soc.  C.  E.,  1897,  xxxvm.  p.  27. 

t  Report  of  J.  R.  Freeman  on  the  water-supply  of  New  York  City,  1900. 

J  Ogden.     Sewer  Design  (New  York,  1899).     §  Eng,  News,  1896,  xxxv.  p.  130. 

||   Reports  of  city  officers,  1895.     ^  Report  by  D.  W.  Mead,  10^5. 


VARIATIONS  IN  CONSUMPTION. 


Moines,  43  gallons ;  Rockford,  90  gallons ;  and  Rock  Island,  200 
gallons.  It  will  be  noted  that,  in  general,  those  places  having  the 
largest  consumptions  show  the  smallest  percentage  variation  through- 
out the  day.  This  is  due  to  the  excessive  leakage  and  waste  which 
occurs  in  these  places,  and  which  is  nearly  uniform.*  If  the  maximum 
ratios  of  the  diagrams  be  multiplied  by  the  maximum  daily  ratio  of, 
say,  150  per  cent,  there  results  for  the  maximum  hourly  ratios  for  the 
entire  year  the  values  175,  210,  180,  238,  220,  and  183  per  cent, 
respectively.  Regarding  rates  for  longer  periods  than  one  hour  it  is 
to  be  noted  from  the  diagram  that  a  rate  nearly  equal  to  the  maximum 
is  likely  to  continue  for  4  or  5  hours. 

To  illustrate  the  effect  of  temperature  and  precipitation  upon  the 
daily  consumption  and  its  variation,  four  diagrams  of  hourly  consumption 
for  Detroit  are  given  in  Fig.  5a.f  Curve  I  represents  the  effect  of 
extreme  cold  weather;  curve  II  that  of  hot  dry  weather;  curve  III 
average  conditions ;  and  curve  IV  Sunday  consumption. 

200 


{75 


50 


-4 


A 


•I 


2! 


I  /50%  of  Yearly  Consumpticn 

II  &*•     » 

in  /oo% "    " 


i     i 


i     i 


i     i 


46       8 

A.M. 


/0/22 


/0/224       66 
Noon  f>M. 

Hour 
FIG.  5a.  —  HOURLY  VARIATIONS  IN  CONSUMPTION,  DETROIT,  MICH. 

3.2.  Consumption  for  Large  Fires.  —  Large  fires  occur  but  seldom, 
and  in  most  of  the  statistics  already  given,  especially  those  relating  to 
hourly  rate,  it  is  safe  to  say  that  nothing  more  than  an  ordinary  fire 
has  been  involved,  such  as  would  require  much  less  than  the  maximum 

*  This  point  is  well  brought  out  by  Mr.  J.  R.  Freeman  in  his  report  on  the  water. 
supply  of  New  York  City,  in  which  he  shows  graphically  that  the  hourly  rates  of  con- 
sumption of  New  York,  Brooklyn,  Fall  River,  and  Woonsocket  differ  by  nearly  a  constant 
quantity,  although  the  average  daily  consumptions  are  widely  different.  (See  Eng.  Record^ 
1900,  XLII.  p.  103.)  t  Trans.  Am.  Soc.  C.  E.,  1901,  XLVI.  p.  413. 


32  QUANTITY  OF   WATER   REQUIRED. 

rate  of  supply.  The  consumption  for  large  fires  must  then  be  consid- 
ered in  addition  to  the  rates  given  above. 

The  maximum  rate  of  fire  consumption  in  gallons  per  capita  per 

day  for  a  town  or  city  of  average  character  may  be  taken  equal  to  — ^-, 

V* 

where  x  =  population  in  thousands.  This  is  based  on  Kuichling's 
estimate  of  the  required  number  of  fire-streams,*  and  assumes  250 
gallon  streams. 

If  the  average  consumption  is  100  gallons  per  capita,  then  the  fire 
rate  in  per  cent  of  the  average  will  be  as  follows  for  different-sized 
cities : 

Rate  of  Fire  Consumption  in  Percentage 

Population.  of  Average,  when  Average  equals  100 

Gallons  per  Day. 

1,000 1000  per  cent. 

5.000 447 

10,000 316 

50,000 I4I 

100,000 100 

200,000 71 

300,000 58 

500,000 45 

For  other  average  values  of  the  daily  consumption  the  percentages 
would  vary  accordingly,  being  greater  for  smaller  consumptions.  In 
the  case  of  small  cities  the  fire  rate  is  evidently  the  principal  factor  to 
be  considered;  in  large  cities  it  is  of  much  less  relative  importance. 
The  duration  of  the  above  rate  of  fire  consumption  may  be  several 
hours ;  it  has  been  estimated  by  Freeman  at  about  six  hours  as  a  maxi- 
mum for  the  full  number  of  streams. 

33.  Maximum  Hourly  Rate. — The  chance  of  a  large  fire  occurring 
at  the  same  time  as  the  maximum  consumption  for  other  purposes  is 
exceedingly  remote,  so  that  in  obtaining  the  probable  hourly  maximum 
some  reduction  may  be  made  in  the  figure  obtained  by  combining  both 
maxima. 

The  maximum  hourly  rate  for  a  city  of  50,000  inhabitants,  with 
100  gallons  per  capita  as  the  average  consumption,  may,  for  example, 
be  estimated  about  as  follows : 

Maximum  daily  ratio  =  175  per  cent  of  average. 

Max.  hourly  ratio  of  maximum  daily  =150  per  cent  of  175  per  cent 
=  262  per  cent  of  average. 

Fire  consumption =  141    "      "      "         " 

Total =  4Q3    "      "      "  , 

*  Trans.  Am.  Soc.  C.  E.,  1897,  xxxvin.  p.  16.  For  further  discussion  of  this 
subject  see  Chapter  XXVIII. 


CONSUMPTION  IN  EUROPEAN  CITIES. 


33 


This  total  may  be  reduced  to,  say,  375  per  cent  of  the  average,  or  375 
gallons  per  day,  as  the  maximum  rate.  It  would  not,  however,  be  safe 
to  assume  a  much  lower  rate,  as  the  average  daily  for  an  entire  month 
is  likely  to  be  '130  per  cent  of  the  average,  which  would  give  for  the 
ordinary  hourly  maximum  130  x  150  =  195  per  cent.  Adding  the  fire 
demand,  the  maximum  becomes  336  per  cent,  or  336  gallons  per  day. 

34.  Consumption  in  European  Cities. — The  consumption  of  water  in 
European  cities  is  much  less  than  in  American  cities.  This  is  due  in 
part  to  the  more  general  use  of  meters  in  Europe,  but  it  is  also 
undoubtedly  true  that  water  is  used  less  lavishly  and  wastefully  there 
than  here.  Moreover,  in  the  United  States  much  more  water  is  lost 
by  leakage,  the  pipes  usually  being  much  larger  and  in  many  cases 
probably  not  so  well  laid.  It  is  believed,  however,  that  a  considerable 
part  of  the  difference  is  due  to  a  greater  legitimate  demand  in  this 

TABLE    NO.  4. 

CONSUMPTION    OF   WATER    IN    EUROPEAN    CITIES. 


City. 

Estimated 
Population. 

1  Consumption  per  Capita 
Daily.  Gallons. 

City. 

Estimated 
Population 

Consumption  per  Capita  j 
Daily.  Gallons. 

England,  1896-97  :* 

5,7OO,OOO 

849,093 
790,000 
680,140 
436,260 
420,000 
415,000 
272,781 
165,000 
93,575 

1,427,200 
330,000 
281,700 
276,500 
144,600 
139,800 
89,700 
62,OOO 

2,500,000 
406,919 
401,930 

42 
40 

34 

28 

31 
43 

21 
24 

43 
59 

18 

20 

34 

21 

25 
26 

78 

20 

53 
202 

3i 

France,    1892  (Bechmann): 

252,654 
148,220 
125,000 
107,000 
70,778 
60,855 

481,500 

437,419 
192,000 
130,000 
8o,000 
7O,OOO 
515,000 
240,000 
489,500 
1,365,000 
960,000 
8lO,OOO 
423,600 
680,000 

58 
26 
13 
32 
3 
264 

53 
264 

21 
II 

60 

61 

20 

53 

20 
2O 
40 

61 
38 
34 

Liverpool  

Nantes  

Birmingham 

Rouen  

Bradford  

Brest  

Leeds  

Sheffield  

Other     countries,     1892-96 
(Bechmann): 

Naples 

Nottingham    • 

Brighton  

Plymouth  

Rome 

Germany,  1890  (Lueger): 
Berlin  

Florence  

Zurich 

Dresden  

Diisseldorf  

Rotterdam 

Stuttgart  

Brussels 

Dortmund  

Vienna  •  . 

St    Petersburg 

France,  1892  (Bechmann): 

Bombay  

Marseilles  

Lyons     

*  Compiled,  except  the  figures  for  London,  by  Hazen.    Eng.  News,  1899,  XLI.  p.  in. 


34 


QUANTITY  OF   WATER  REQUIRED. 


country  ;  a  demand  caused  in  some  cases  by  a  higher  commercial  con- 
sumption and  in  general  by  a  larger  domestic  use  due  to  the  less 
economical  habits  of  the  people  and  to  the  use  of  a  larger  number  of 
fixtures.  In  Table  No.  4  is  given  the  consumption  per  capita  for 
several  cities  in  various  European  countries. 

The  use  of  water  for  public  purposes  in  seven  German  cities  varied 
from  i  to  12  gallons  per  capita  in  1888-1890,  this  being  from  2  per 
cent  to  33  per  cent  of  the  total  consumption.  In  Berlin  2.5  per  cent 
is  used  for  street-sprinkling,  3  per  cent  for  sewer-flushing,  and  7  per 
cent  for  fountains.  In  Dresden  3.7  per  cent  of  the  entire  consumption 
is  used  for  public  fountains.*  In  Paris  35  per  cent,  or  20  gallons  per 
capita,  is  used  for  street-washing. 


J60 


FIG.  6.  —  PERCENTAGE  GROWTH  OF  CITIES. 

35.  Growth  of  Cities.  —  A  necessary  factor  in  any  estimate  of  future 
consumption  is  that  of  future  population.  The  rate  of  growth  of  differ- 
ent cities  is  exceedingly  various,  but  of  any  one  city  it  is  likely  to  be 

*  Handbuch  der  Ingenieurwissenschaften,  p.  69. 


GROV/TH  OF  .CITIES* 


35 


fairly  constant  for  several  years,  or  at  least  will  vary  but  slowly.  The 
older  and  the  larger  the  city  the  more  uniform  the  rate  of  growth,  and, 
barring  national  disasters,  a  fairly  close  estimate  can  be  made  for  two 
or  three  decades  in  the  future.  In  the  case  of  many  American  cities 
the  rate  is  still  undergoing  large  variations,  and  predictions  are  very 
uncertain. 

For  a  city  with  a  steady  rate  of  growth  the  percentage  added  eacfr. 
decade  or  shorter  period  is  very  nearly  constant;  and  to  estimate  the 
future  population  it  is  only  necessary  to  apply  this  constant  percentage 
successively  for  as  many  periods  as  desired.  If  the  percentage  is 
changing,  then  a  varying  rate  must  be  used,  which  can  only  be  pre- 
dicted by  a  study  of  the  changes  in  the  rates  in  past  years  and  a 
knowledge  of  such  local  conditions  as  are  likely  to  affect  the  city's 
growth.  To  facilitate  such  estimates  the  percentage  increase  for  each 
decade  should  be  plotted,  and  any  marked  tendency  to  change  can  then 
be  allowed  for  in  extending  the  curve  forward. 

In  Fig.  6  are  plotted  such  percentages  for  several  cities  of  differing 
characteristics.  The  percentages  for  London  are  remarkably  constant,, 


cx**w 

// 

/ 

«; 

^ 

/  / 

/' 

isoqooo 

SOQpOO 
£ 

, 

^ 

£l 

.>"''' 

ti 

^?' 

v 

<$'' 

'" 

/ 

^> 

-''' 

^ 

•'$:- 

•^ 

f 

^ 

r' 

^^ 

^f 

i£* 

S 

rd 

Boston 
Londo, 

CTen- 
7  (/nne 

wile  C/t 

c/<?y 

Pop. 

96  m 

10  in 

/302 

^ 

^* 

Ber/ir. 

Pfi/too 

f/ac/ut 

fafdi 

'burtis 
•  Ore  A. 

J 

• 

• 

7OJJ 

1672 

C/?/c<r< 

JO 

• 

- 

• 

/<S<9d 

5     20      IS      /O       S       0       S      /O      /S     20      IS     30      JJ"     •*)    45 

Years  Before  and  After  r?eacn/ng  a  Popu/af/on  of  967,000 

FIG.  7.— POPULATION  CURVES  PLOTTED  WITH  REFERENCE  TO  BOSTON,  MASS. 
and  in  estimates  for  the  future  a  rate  of  20  might  reasonably  be 
assumed.  Several  of  the  other  cities  have  reached  a  nearly  uniform 
rate,  while  in  some  the  rate  is  still  likely  to  undergo  great  changes. 
In  estimating  the  population  of  London  for  forty  years  in  the  future  the 
Royal  Commission  in  1893  used  the  percentage  for  the  decade  1881  to 
1891,  a  value  of  18.2.  The  data  for  Boston,  New  York,  Philadelphia* 


36  QUANTITY  OF    WATER  REQUIRED. 

and  Chicago  are  as  compiled  by  Brackett  in  Appendix  No.  I  of  the 
Report  of  the  State  Board  of  Health  of  Massachusetts  upon  a  Metro- 
politan Water-supply.  They  represent  in  each  case  the  population 
within  a  I  5  mile  radius. 

36.  Another  method  of  estimating  future  population  is  to  study  the 
growth  of  various  larger  cities  from  the  period  at  which  their  population 
equaled  the  present  population  of  the  city  in  question;  and,  taking 
account  of  differing  characteristics,  to  deduce  therefrom  the  probable 
future  population  required.  This  method  was  used  as  an  aid  in  predict- 
ing the  future  population  of  Boston  in  the  report  above  referred  to,  and 
the  diagram  employed  is  reproduced  in  Fig.  7.  It  exhibits  the  curves 
for  several  cities,  so  plotted  as  to  intersect  at  the  point  corresponding 
to  a  population  of  967,000,  the  population  of  Boston  in  1894. 

An  objection  to  this  method  of  estimation  is  that  it  is  based  upon  a 
comparison  of  rates  of  growth  of  cities  of  widely  varying  characteristics, 
and  of  rates  relating  to  very  different  periods  of  time.  Thus  the  growth 
of  Boston  in  1 900  is  compared  with  that  of  New  York  in  1 860,  when 
industrial  conditions  were  materially  different  from  those  at  the  present 
time. 

LITERATURE. 

1.  Harlow.     The   Consumption  and  Waste  of  Water  delivered    by  Public 

Works.     Trans.  Am.  Soc.  C.  E. ,   1877,  vi.  p.   107. 

2.  Brush.     Some  Facts  in  Relation  to  Friction,  Waste,  and  Loss  of  Water 

in  Mains.     Trans.  Am.  Soc.  C.  E.,   1888,  xix.  p.  89. 

3.  Manual  of  American  Water- works.      1890-1  and  1897. 

4.  Freeman.     The  Arrangement  of  Hydrants  and  Water-pipes  for  the  Pro- 

tection of  a  City  against  Fire.     Jour.  New  Eng.  W.  W.  Assn.,   1892, 
vii.  p.  49 

5.  Report  of  the  Royal  Commission  on  the  Water-supply  of  the  Metropolis. 

London,  1893. 

6.  Halbertsma.      Dichtigkeitsproben   an   Rohrnetzen.     Jour.    f.    Gasbel.    u. 

Wasservers.,  1894,  xxxvu.  p.  722. 

7.  Brackett.     Consumption  and  Waste  of  Water.     Trans.  Am.  Soc.  C.  E., 

1895,  xxxiv.  p.   185. 

8.  Kuichling.     The  Financial   Management  of  Water-works.      Trans.   Am. 

Soc.  C.  E.,  1897,  xxxvin.  p.  i. 

9.  Crandall.      Loss  of  Water  from  Pipes.     Jour.  New  Eng.  W.    W.   Assn., 

1898,  xii.  p.  245. 

10.  Report  on  the  Extension  and  Improvement  of  the  Water-supply  of  Phila- 

delphia,   1899.      Abstract,   Eng.   News,     1899,    XLII.    p.    230;  Eng. 
Record,  1899,  XL.  p.  404. 

11.  Freeman.      The    Water- waste    and    Water  supply    of    New    York    City. 

Report  to  the  Comptroller.      1900. 

12.  The  Water-supply   of  the  City   of    New   York.      1900.      Issued   by  the 

Merchants'   Association.      Contains  reports  by  J.   J.  R.  Croes   and 
Foster  Crowell  on  the  use  and  waste  of  water. 


GROWTH  OF  CITIES.  37 

13.  Bailey.     The    Effect  of   Water   Meters    on  Water    Consumption    in   the 

Larger  Cities  of  the  United  States.     Eng.  News,  1901,  XLV.  p.  279. 

14.  The  Consumption  of  Water  in  Municipal  Supplies  and  the  Restriction  of 

Waste.     Discussion.     Trans.  Am.  Soc.  C.  E.,  1901,  XLVI.  p.  407. 
15     The  Consumption  of  Water  in  Cities  and  Towns  in  Massachusetts.     Re- 
port, Mass.  Board  of  Health,  1900.     Eng.  News,  1902,  XLVIII.  p.  414. 

1 6.  Report  of   the  Commission    on  Additional  Water-supply  for  New  York 

City,   1904,  App.  ix.  p.  945. 

17.  Shedd.     Requisite  Amount  of  Water  for  a  Public   Supply.     Jour.  New 

Eng.  W.  W.  Assn.,   1904,  xvm.  p.    i. 

1 8.  Brackett.     Report   on   the    Measurement,    Consumption    and    Waste    of 

Water  Supplied  to  the  Metropolitan  Water  District.  Report  Boston 
Met.  Water  Board,  1904,  XLIX.  p.  363.  Jour.  New  Eng.  W.  W.  Assn., 
1904,  xvm.  p.  107. 

19.  Fuertes.     Waste  of  Water  in  New  York  and  its  Reduction  by  Meters 

and  Inspection.  A  Report  to  the  Committee  on  Water-supply  of  the 
Merchants'  Association  of  New  York  City,  1906. 

20.  Johnson.     Some  new  facts  relating  to  the  Effect  of  Meters  on  the  Con- 

sumption of  Water.  Jour.  New  Eng.  W.  W.  Assn.,  1907.  Eng. 
News,  1907,  LVII.  p.  342. 


CHAPTER   III. 
SOURCES   OF   SUPPLY. 

37.  Classification. — The   sources   of  water-supply  may  be   divided 
into   the   following   classes   according   to  the  general  source  and  the 
method  of  collection: 

A.  Surface-waters: 

1 .  Rain-water  collected  from  roofs,  etc. 

2.  Water  from  rivers. 

3.  Water  from  natural  lakes. 

4.  Water  collected  in  impounding  reservoirs. 

B.  Ground- waters : 

5.  Water  from  springs. 

6.  Water  from  shallow  wells. 

7.  Water  from  deep  and  artesian  wells. 

8.  Water  from  horizontal  galleries. 

Each  of  the  above  sources  except  the  first  and  last  are  at  present  fur- 
nishing many  cities  in  the  United  States  with  a  more  or  less  satisfactory 
water. 

38.  Quality  of  Water  from  Various  Sources. — The    kind    of  water 
which  a  region  can  furnish  depends  on  its  climatic,  geologic,  and  topo- 
graphic  features.       Much  good   water  has  been   obtained  from  small 
streams   in   the  rougher  portions  of  the  United   States  where  sites  for 
reservoirs  can  readily  be  found  and  where  collecting  areas  are  sparsely 
populated;  but  in  a  large  portion  of  the  country  such  a  source  of  supply 
is  impracticable  or  undesirable,  and  in  these  localities  we  find  that  the 
ground-water    supplies    have    been    more    largely   developed.       Many 
supplies  drawn  from  lakes  and  rivers  are  also  in  use  in  all  parts  of  the 
country,  but  until  some  method  of  purification  is  generally  adopted  they 
will  not  be  as  a  rule  very  satisfactory.      These  sources  must,  however, 
continue  to  furnish  a  large  and  increasing  number  of  cities  with  water 
as  the  supplies  from  the  first-mentioned  source  become  more  and  more 
fully  utilized. 

Ground-waters  are  as  a  rule  of  better  quality  from  a  sanitary  point 

38 


UTILIZATION  OF   THE    VARIOUS  SOURCES. 


39 


of  view  than  surface-waters,  but  in  many  cases  they  will  not  be 
altogether  satisfactory  until  processes  for  the  removal  of  iron  and  of 
hardening  impurities  are  adopted. 

39.  Utilization  of  the  Various  Sources. — The  following  table  gives 
the  number  of  water-works  obtaining  their  supply  from  the  various 
sources  indicated,  and  the  percentage  of  the  total  number  supplied  from 
each  source.  Under  Northeastern  States  are  included  Pennsylvania, 
New  Jersey,  and  all  to  the  north  and  east;  North  Central  includes  all 
others  to  the  north  of  the  Ohio  River  and  east  of  the  Mississippi  River ; 
Southeastern,  all  remaining  States  east  of  the  Mississippi;  and  Western, 
all  west  of  it* 

TABLE   NO.  5. 

SOURCES    OF   WATER-SUPPLIES    IN   THE    UNITED    STATES. 


Source. 

Northeastern 
States. 

Southeastern 
States. 

North  Central 
States. 

Western 
States. 

Total 
Number. 

Per  cent  of 
Grand  Total. 

Surface-waters: 

iif\ 

t  TA 

ocf\ 

Roc 

33° 

A 

117 
f\o 

250 

025 

6f. 

129 

24 
A(\ 

6     a 

1J5 

4° 

213 

•3 
Of. 

•15 

3 

Total  

ATc 

~Q     ff 

Ground-waters. 
Shallow  wells               

O1D 

A4J 

193 

329 

oQr» 

Q£  - 

3».2 

I3O 

41 

nR 

300 

25-7 

39 

59 

9» 

J45 

341 

Galleries  and  tunnels  

300 

72 

27 

103 

14.9 

Combinations  ....    

9 

Q 

!3 

34 

R/i 

33 

04 

2.  5 

Total  

rfin 

AA.> 

Surface-  and  ground-waters. 

511 

TA 

409 

fir 

54«2 

6T 

v^ 

37 

T  A. 

4 

31 

0.9 

L7 

•  5 

Total  

7f. 

X7 

53 

72 

254 

.0 

T  OT  Q 

34° 

7*5 

335O 

No.  of  Works. 


The  number  of  filtered  supplies  in  1 896  was  as  follows : 

Surface-waters. . . . , 179 

Ground-waters 23 

Surface-  and  ground-waters 29 


Total 


231 


*  From  Eng.  News,  1898,  XL.  p.  9,  and  Manual  Am.  W.  W.,  1897. 


40  SOURCES   OF  SUPPLY. 

In  Europe  a  much  larger  proportion  of  the  public  supplies  is  derived 
from  ground-water  sources  than  is  the  case  in  this  country.  In 
Germany,  for  example,  in  1884,  of  the  total  population  having  a  public 
water-works  the  following  percentages  drew  their  supply  from  the 
various  sources  indicated :  * 

River-  and  other  surface-water 27.9  per  cent. 

Spring-water 13.8    "      " 

Other  ground-water 58.3    "       " 

In  France,  out  of  a  total  population  of  about  12  millions  living  in 
cities  of  over  5000  inhabitants,  the  following  percentages  were,  in 
1892,  supplied  with  water  from  the  sources  indicated  :t 

Rivers 14  per  cent. 

Springs 23     "      " 

Other  ground-water •. 14     "      " 

Combinations  . 49     "      " 

*  Jour.  f.  Gasbel  M.  Wasservers.,  1884,  p.  411. 

f  Bechmann.     Distribution  d'eau  (Paris,  1899),  n.  p.  330. 


CHAPTER  IV. 


THE   RAINFALL. 

40.  The  rainfall  being  manifestly  the  source  of  all  water-supply, 
whether  caught  as  it  flows  over  the  surface  or  first  allowed  to  percolate 
into  the  ground  to  furnish  water  for  wells  and  springs,  it  is  desirable 
to  commence  the  discussion  of  the  quantity  available  from  the  different 
sources  with  a  study  of  the  rainfall.      The  yield  of  a  given  source  is  the 
product  of  several  factors,  of  which  the  rainfall  is  but  one;  and  in  many 
cases  it  is  quite  as  easy  or  even  easier  to  estimate  the  value  of  this 
product  directly  as  to  determine  it  from  a  consideration  of  the  several 
factors.      In  other  cases,  however,  this  cannot  be  done,  and  to  enable 
the  data  already  collected  regarding  the  various  elements  to  be  intelli- 
gently used  in  the  solution  of  new  problems,  a  careful  study  of  each  of 
these  elements  is  necessary. 

41.  Measurement  of  Rainfall. — The  amount  of  rainfall  is  expressed 
in  inches  of  depth  upon  a  horizontal  surface,  snowfall  being  reduced  to 


UJ. 


FIG.  8. — ORDINARY  RAIN-GAUGE. 

its  equivalent  amount  of  rainfall.     The  ordinary  rain-gauge  used  by 
the  Weather   Bureau   is  illustrated  in  Fig.   8.     The   diameter  of  the 

41 


42  THE   RAINFALL. 

receiver  A  is  8  inches,  and  the  entire  height  of  the  instrument  is 
2  feet.  The  rim  is  beveled  to  a  sharp  edge  and  is  accurately  circular. 
The  water  which  falls  into  the  receiver  is  conveyed  into  the  collecting- 
tube  C,  of  one-tenth  the  cross-section  of  the  receiver,  and  the  amount 
of  water  so  collected  is  determined  by  a  measuring-stick  of  cedar.  In 
this  way  small  rainfalls  can  be  readily  measured.  Large  rainfalls 
overflow  into  the  outer  cylinder,  which  is  also  used  as  a  collector  for 
snow. 

While  the  actual  measurement  is  thus  simple,  the  collection  of  the 
correct  amount  of  water  is  not  easy.  It  is  found  that  the  amount  of 
water  collected  depends  largely  upon  the  location  of  the  gauge. 
Variations  as  great  as  50  per  cent  have  been  observed,  due  to  differ- 
ences in  location  in  regard  to  buildings  and  other  objects,  and  to  the 
elevation  of  the  gauge  above  the  ground.  In  general  the  greater  the 
elevation  of  the  gauge  the  less  the  amount  of  water  collected.  The 
reason  for  this  has  been  quite  conclusively  shown  to  be  due  to  the 
greater  velocity  of  the  wind  at  the  greater  elevation,  less  water  being 
collected  the  stronger  the  wind.* 

The  errors  of  collection  due  to  wind  eddies  caused  by  buildings, 
trees,  etc.,  are  of  much  greater  importance  than  those  due  to  elevation, 
and  to  avoid  these  the  gauge  should  be  located  some  distance  from  all 
disturbing  objects  and  not  much  above  the  ground.  In  cities,  the  best 
place  is  on  the  roofs  of  flat  buildings,  and  this  is  the  location  usually 
selected  by  the  Weather  Bureau.  Such  locations,  though  free  from 
disturbances  caused  by  other  buildings,  are  not  as  trustworthy  as  is 
desirable,  and  it  is  estimated  by  the  Bureau  that  the  amounts  regis- 
tered by  its  gauges  are  from  5  to  10  per  cent  too  small. t 

Besides  inaccuracies  due  to  exposure,  there  are  slight  inaccuracies 
in  the  measurement  of  small  rainfalls  in  dry  weather  due  to  evaporation 
from  the  gauge,  and  very  considerable  errors  in  the  measurement  of 
snowfalls. 

With  the  ordinary  rain-gauge  it  is  impracticable  to  determine  rates 
of  rainfall  for  short  periods  of  time,  the  records  usually  obtained  from 
these  gauges  being  merely  the  total  amounts  of  rainfall  for  each 
twenty-four  hours.  For  estimating  flood-volumes  from  small  areas, 
however,  it  is  important  to  know  the  rate  of  rainfall  for  much  shorter 
periods  than  one  day.  For  this  purpose  self-recording  gauges  are 
essential,  that  is,  gauges  which  give  a  continuous  record  of  the  rainfall 
or  a  record  taken  at  such  short  intervals  as  to  be  for  all  practical  pur- 


*See  reference  (2),  p.  50. 

f  Bulletin  D,  Weather  Bureau,  1897,  p.  9. 


RAINFALL   STATISTICS.  43 

poses  continuous.     Various  forms  have  been  devised,  some  weighing 
the  water,  others  recording  by  volume.* 

42.  Rainfall  Statistics  for  a  large  number  of  stations  can  now  be 
readily  obtained    from  the  monthly  reports  of  the  Weather  Bureau. 
Since   1888  observations  relating  to  excessive  rainfalls  have  been  made 
with  self-recording  rain-gauges,  the  number  of  stations  provided  with 
such  gauges  in   1900  being  about  seventy.     The  data  of  importance  in 
connection  with  water-supply  questions   are  the  mean  yearly  rainfall, 
the   deviation   from  this  in  dry  years,  the  monthly  rainfall,  and  finally 
the  maximum  depth  of  rain  falling  in  a  single  day  or  less. 

43.  Mean  Annual  Rainfall. — The  mean  annual  rainfall  and  the  prin- 
cipal  drainage  areas  of  the  United  States  are  shown  in  Fig.  Q.f     The 
maximum  rainfall  is  seen  to  be  along  a  narrow  belt  of  the  North  Pacific 
coast,  where  it  considerably  exceeds  60  inches.     Towards  the  interior 
the  amount  rapidly  falls  off,  and  between  the  Sierras  and  the  Rocky 
Mountains  it  ranges  from  5  to  1 5  inches.     East  of  the  Rockies  there  is 
a  gradual   increase   eastward   and  southward   to  a  maximum  along  the 
Gulf  of  60  inches,  and  from  40  to  50  inches  on  the  Atlantic  coast. 

44.  Secular  Variations  in  the  Rainfall. — The  question  of  a  gradual 
change  in  the  yearly  rainfall  is  one  the  solution  of  which  would  doubt- 
less require  data  covering  several  centuries.     The  rainfall  for  a  partic- 
ular locality  may  average  considerably  below  the  mean  for  many  years, 
after  which  may  follow,  perhaps,  an   equally  long  period  of  surplus. 
In  an   analysis  of   several  records   extending  over  many  years  it  was 
found  that   during  an  83-year  period  at  New  Bedford,  Massachusetts, 
the  averages  for  ic-year  periods  were  as  high  as  16  per  cent  above  the 
mean  and  n  per  cent  below;  for  6o-year  periods  the  extremes  were,  at 
St.  Louis,  17  per  cent  and   13  per  cent,  and  at  Cincinnati,  20  per  cent 
and    17  per   cent.     For  a  2  5 -year  period  the  extreme  variations  were 
10  per  cent  for  both  New  Bedford  and  St.  Louis.  \ 

The  variations  or  cycles  above  referred  to,  that  extend  over  several 
years,  are  in  some  cases  very  marked,  but  they  are  very  erratic  and  as 
yet  quite  incapable  of  being  predicted.  In  Fig.  10  are  plotted  what 
are  called  progressive  averages  of  precipitation  for  three  sections  of  the 
country,  and  the  actual  precipitation  for  Madison,  Wisconsin,  for  a 
number  of  years.  The  progressive  averages  for  each  section  are  found 
by  first  averaging  the  yearly  rainfalls  for  three  or  four  stations ;  then 

*  For   a   description   of   various  forms    of    self-recording   gauges    see    references    (7) 
and  (9),  p.  51. 

t  From  a  paper  by  John  C.  Hoyt  in  Trans.  Am.  Soc.  C.  E.,  1907,  Lix.  p.  431. 
J  Bulletin  D. 


44 


THE   RAINFALL. 


SECULAR    VARIATIONS  IN    THE   RAINFALL. 


45 


these  averages  are  further  modified  to  give  a  smoother  curve  by  the 
formula 


_ 

C 


FIG.  10. — SECULAR  VARIATIONS  IN  THE  RAINFALL. 

where  a,  b,  c,  d,  and  e  are  the  rainfalls  for  successive  years,  and  c'  is 
the  progressive  average  for  the  middle  year.  In  this  way  any  gradual 
change  in  the  rainfall  can  be  more  clearly  brought  out.  In  the 
diagram  the  ordinates  represent  inches  above  or  below  the  mean.  The 
gradual  increase  for  a  long  period  of  time  in  the  rainfall  at  the  stations 
representing  New  England  is  very  striking,  although  this  is  shown  by 
other  records  to  be  quite  local  in  extent.  Other  changes  for  consider- 
able lengths  of  time  are  to  be  noted  in  the  diagram,  and  it  is  clearly 
to  be  seen  that  a  record  covering  twenty  or  thirty  years  is  of  no  value 
in  studying  the  question  of  secular  variation.  The  diagram  for 


46  THE   RAINFALL. 

Madison,  Wisconsin,  is  of  course  very  rough,  but  shows  the  same 
general  variation  as  that  just  above  it.  If  the  portion  of  the  curve  for 
the  years  1880  to  1895  alone  be  considered,  a  very  rapid  and  persistent 
decrease  in  the  rainfall  would  be  noted. 

45.  Mean  Monthly  Rainfall. — The  monthly  distribution  of  the  rain- 
fall is  of  great  importance  in  all  questions  relating  to  the  utilization  of 
water  for  power  purposes  or  for  the  supply  of  cities.  The  rain  falling 
in  the  summer  months,  when  vegetation  is  using  a  maximum  of  water 
and  evaporation  is  rapid,  is  of  but  little  value  for  supplying  water  to  the 
streams.  It  is  the  winter  and  spring  rains  which  must  largely  be  relied 
upon  to  fill  reservoirs  and  to  raise  the  low  ground-water  to  its  normal 
level. 

Fig.  1 1  *  shows  graphically  the  mean  monthly  distribution  of  the 
rainfall  for  several  stations  representative  of  the  different  sections  of  the 


•ppinni  ii  ii  ii  innnn  n  inni  n  imi  u  n  HI  n  11 11  IHHHI  HI 


FIG.  u. — MONTHLY  VARIATIONS  IN  RAINFALL. 

country.      The  ordinates  represent  the  percentage  of  the  total  yearly 
rain  falling  in  the  month. 

In  the  eastern  and  southern  parts  of  the  country  the  distribution  is 
quite  uniform,  the  variation  here  being  greatest  along  the  south  Atlantic 
coast,  as  shown  in  the  diagram  for  Charleston.  As  we  go  farther 
north  and  west  to  Detroit,  Madison,  and  North  Platte,  a  great  change 

*  Bulletin  D. 


MINIMUM    YEARLY  RAINFALL. 


takes  place,  a  larger  and  larger  percentage  of  the  rain  falling  in  the 
summer  months.  This  is  a  very  advantageous  distribution  for  vegeta- 
tion, but  a  very  poor  one  for  furnishing  surplus  water.  The  diagram 
for  Santa  Fe  is  typical  of  New  Mexico  and  Arizona,  and  that  for 
Spokane  of  the  northern  plateau.  The  distribution  along  the  entire 
Pacific  coast  is  very  similar  to  that  at  San  Francisco. 

Numerical  data  relating  to  the  distribution  of  the  yearly  rain  are 
given  in  Table  No.  6. 

46.  Minimum  Yearly  Rainfall. — In  Table  No.  6  are  given,  for 
several  representative  stations,  the  mean  yearly  rainfall ;  the  propor- 
tion of  the  yearly  rain  falling  during  the  six  months  from  June  to 
November,  inclusive;  the  percentage  of  the  mean  yearly  rain  which 
fell  in  the  driest  year  covered  by  the  records ;  the  percentages  for  the 
two  driest  consecutive  years,  and  likewise  for  the  three  driest  consecu- 
tive years ;  and  the  number  of  years  of  records  from  which  the  data 
have  been  collected.  The  records  close  with  1896. 

TABLE    NO.  6. 

GENERAL    RAINFALL    STATISTICS    FOR    THE    UNITED    STATES. 


Station. 

G 

'c5 
Pt 
>> 

3 

of  Summer 
utumn  Rain 
*n  Yearly. 

t  Driest  Year 
an  Year. 

'C 

Q 

1. 

Q 

V 

£ 

M 

i 

I 

o  . 

> 

S3 

Per  cen 
and  A 
to  Me 

Per  cen 
to  Me 

Per  cen 
estYe 

Per  cen 
estYe 

£8 

il 

£ 

North  Atlantic  : 

A  c    A 

CO 

60 

7O 

80 

7Q 

AC      8 

co 

74 

78 

82 

/y 

4  H 

New  York                  

A  A      7 

C2 

62 

77 

80 

6l 

42    ^ 

C2 

7O 

7C 

So 

72 

42    Q 

c  i 

60 

71 

74 

JC 

South  Atlantic: 

e-5    7 

61 

7C 

8O 

81 

26 

OJ'  1 

AQ  .  I 

61 

48 

cc 

62 

80 

48  o 

CO 

81 

88 

87 

C.A.  I 

t>< 

74 

77 

8^ 

27 

Key  West                  

q»    2 

7O 

61 

7-2 

/1Q 

Gulf  and  Lower  Mississippi: 

48    2 

A'i 

67 

7c 

7C. 

2C. 

S2    ^ 

42 

76 

80 

8q 

24. 

62  6 

ci 

68 

7e 

78 

26 

60  ^ 

CO 

64 

7c 

77 

26 

47.  7 

58 

CQ 

6e. 

72 

26 

Nashville    

CQ     2 

46 

67 

7-7 

8a 

oo 

Vicksburg.  

C2    7 

4^ 

7O 

74 

R-i 

42 

Ohio  Valley: 

^6.6 

C-3 

7O 

78 

8q 

42.  1 

CQ 

60 

72 

71 

62 

42    2 

c  r 

CQ 

76 

82 

27 

17    o 

48 

74 

81 

8s 

or 

Cairo  

42.6 

47 

62 

75 

81 

25 

48 


THE   RAINFALL. 


TABLE    NO.  6.— Continued. 

GENERAL    RAINFALL    STATISTICS    FOR    THE    UNITED    STATES. 


Station. 

G 

"3 

Pi 
>, 
1 
I 

G~ 

££ 
& 

Per  cent  of  Summer 
and  Autumn  Rain 
to  Mean  Yearly. 

Per  cent  Driest  Year 
to  Mean  Year. 

Q 
o 

H£- 

«J    Cfl 

§> 

Is 

Per  cent  Three  Dri- 
est Years. 

Number  of  Years' 
Record. 

Lake  Region: 

00       O. 

«?8 

60 

7e 

QT 

$*•  3 

oo    e 

^6 

6< 

72 

jJ 
Af) 

36  6 

CJ4 

71 

74 

/V 

81 

on    7 

61 

6<; 

81 

88 

26 

Upper  Mississippi  Valley: 

do  8 

^2 

c  e 

6=; 

7e 

60 

oo    q 

58 

t;6 

68 

70 

26 

o  j     o 

CA 

66 

80 

86 

0  T      O 

c  c 

66 

74 

Ju 

C-5 

00       0 

*8 

OQ 

eR 

Jj 
68 

r>j 
28 

<3O    7 

6^ 

C7 

78 

7Q 

24 

St    Paul  i.    .    ,.  

28.2 

6-? 

eo 

£4 

/v 

7e 

OQ 

The  Plains: 

"31  .  d 

6-3 

£7 

6-; 

7O 

27 

TQ    8 

62 

CJ 

«;8 

7<j 

22 

18.1 

61 

«^6 

67 

72 

22 

14..  3 

48 

CQ 

71 

77 

27 

TO    7 

ee 

•3Q 

62 

7d 

27 

The  Plateau: 

2    8 

<3Q 

2C 

en 

46 

21 

7  .  1 

4Q 

C2 

88 

QO  ' 

I  ^ 

II  .  7 

6* 

44 

7Q 

80 

IQ 

14.   6 

60 

ea 

6-* 

66 

-77 

12    I 

2C 

S7 

6-^ 

72 

TQ 

18.8 

an 

ce 

6d 

74 

2Q 

18.6 

18 

7-1 

84 

8d 

1C 

Walla  Walla  

jc  .4 

38 

46 

81 

86 

27 

Pacific  Coast: 

77.O 

aa 

64 

68 

77 

34 

46    2 

OJ 

67 

7O 

7Q 

27 

Red  Bluff      

04   4 

07. 

C2 

6d 

e;8 

2C 

IQ    Q 

16 

d2 

67 

8d 

47 

2T    4 

17 

Cl 

7^ 

78 

47 

17    2 

JC 

oa 

d8 

CQ 

2d 

Q    ^ 

18 

61 

6^ 

74- 

IQ 

San  Dieero.  . 

Q.7 

z8 

•^o 

«?d 

61 

d7 

By  an  examination  of  data  relating  to  stream-flow  it  is  found  that 
the  months  from  June  to  November  are  the  six  months  in  which  the 
rainfall  has  in  general  the  least  direct  effect  upon  stream-flow.  The 
percentages  of  the  yearly  rain  falling  in  these  months  have  therefore 
been  given  in  the  table. 

In  England  it  was  formerly  the  practice  in  designing  water-works 
to  assume  as  the  mean  rainfall  for  the  three  driest  years  83^  per  cent 
of  the  mean,  but  further  investigation  led  to  the  adoption  of  80  per  cent 
as  a  more  reliable  figure.  Similar  ratios  have  also  been  made  use  of 


MAXIMUM  KATES   OF  RAINFALL.  49 

to  a  considerable  extent  in  this  country,  but  from  the  above  table  it  is 
evident  that  in  many  localities  it  would  not  be  safe  to  use  over  75  per 
cent,  or  even  less.  The  very  low  percentages  for  some  of  the  stations 
must  be  taken  as  an  indication  of  what  may  occur  at  any  point  in  a 
comparatively  wide  territory  in  each  case.  For  example,  at  Madison, 
Wisconsin,  the  rainfall  in  1895  was  but  39  per  cent  of  an  average,  and 
this  was  both  preceded  and  followed  by  years  of  low  rainfall,  thus 
giving  the  very  low  percentages  of  58  and  68  for  the  two  and  three 
driest  years.  This  extreme  drought  was  very  local,  but  it  shows  what 
may  happen  at  rare  intervals  in  that  part  of  the  country. 

The  lowest  percentages  for  the  one,  two,  and  three  driest  years, 
with  the  exception  of  a  few  extreme  cases,  are  about  the  same  over  a 
large  portion  of  the  United  States  and  may  reasonably  be  placed  at 
about  60,  70,  and  75  per  cent  for  the  East  and  South,  with  a  reduction 
to  50,  60,  and  70  per  cent  respectively  for  the  Northwest  and  plains 
region.  For  the  Rocky  Mountain  region  and  the  Pacific  coast  the 
figures  would  in  many  places  be  much  lower,  but  the  conditions  are 
here  so  varied  that  a  general  statement  would  be  of  no  value. 

47.  Maximum  Rates  of  Rainfall. — In  estimating  the  maximum  flood- 
volumes  of  small  streams — a  matter  of  very  great  importance  in  the 
design  of  dams  and  reservoir  embankments — it  is  desirable  to  know 
the  maximum  rates  of  rainfall  for  periods  of  a  few  hours  or  a  single 
day. 

In  Table  No.  7  are  presented  data  compiled  from  the  Monthly 
Weather  Review  relating  to  excessive  rainfalls.  The  records  cover 
the  period  from  1871  to  1906,  and  all  rainfalls  are  represented  which 
exceeded  in  amount  5  inches  in  twenty-four  hours,  and,  from  1894  to 
1906,  all  those  which  equaled  or  exceeded  2  inches  in  one  hour.  As 
far  as  possible,  the  same  storm  is  represented  but  once  for  any  one 
State,  although  records  may  have  been  received  from  several  stations ; 
and  furthermore  each  storm  is  counted  as  a  one-day  storm  or  a  two-day 
storm,  but  not  both.  A  one-day  storm  is  one  in  which  all  the  rain  falls 
in  a  meteorological  day,  that  is,  from  8  P.M.  to  8  P.M.,  and  in  a  two-day 
storm  all  the  rain  falls  within  two  such  days.  A  one-day  storm  may 
therefore  have  fallen  in  a  few  hours,  and  likewise  a  two-day  storm,  so 
that  the  figures  given  do  not  necessarily  represent  the  maximum  rates. 
However,  by  taking  the  maximum  from  among  a  great  many  records 
the  figures  thus  found  for  the  one-  and  two-day  storms  will  approxi- 
mate the  maximum  for  24  and  48  hours.  The  one-hour  rates  are  well 
determined.  The  number  of  times  a  rainfall  has  exceeded  the  given 
amounts  is  an  indication  of  the  frequency  of  heavy  storms  and  also 


THE    RAINFALL. 


to  some  extent,  of  the  reasonableness  and  reliability  of  the  maximum 
figure.  Those  States  having  the  highest  maximum  rates  are  those 
where  heavy  rainfalls  are  the  most  frequent. 

TABLE    NO.  7. 


MAXIMUM    RAINFALLS. 


State. 

No.  of 

Stations.* 

Hourly  Rate. 

One-day  Storms. 

Two-day 
Storms. 

Maxi- 
mum. 

No.  of 
Storms 
=  or  > 
2  in. 

Maxi- 
mum. 

No.  of 
Storms 
=  or> 

5  in. 

Maxi- 
mum. 

No.  of 
Storms 
=  or> 
5  in. 

Northern  and  Central  States: 
Miaine 

18 

41 
78 
29 
76 

59 
84 

7 
25 

37 
39 
4i 
43 
96 
142 
45 
63 
86 
64 

$ 

82 
69 
87 
79 

56 

48 
62 
34 
52 
5i 
54 
81 

48 

279 
94 

3.00 
2.29 
4.49 

3-35 
2.58 
3-20 

I 
2 

3 
6 

IO 

5-6i 

7.41 
6.60 
7.40 
IO.  IO 

8.73 
8.37 

I 
I 
2 
2 

8 
9 

10 

5-21 
6.79 

8.22 
10.30 
10.04 
10.40 

9-03 
6.79 

T4-75 

6.85 
7.00 
9.67 
8.62 
9.60 
8.06 

10.00 

9-35 
6-34 
10.  15 
7.80 
9.70 
8.40 
10.69 
6-55 
7-39 

13.00 
13.22 
11.52 
13.14 

10.00 

10.  60 

*6-55 
14.78 
9.  10 

2 

I 

9 

10 
12 

6 

i 
3 

9 

i 

13 
3 
17 
7 
6 

14 
4 
3 
6 
6 

17 
8 

4 

4 

26 
23 
3i 

40 

22 

24 

34 
33 
20 

New  Hampshire  and  Vt.  . 
Massachusetts 

Connecticut  and  R.  I.  .    . 

Pennsylvania  

Maryland 

4.64 
3.00 

2.20 
4.00 
2.90 
4-74 
3-32 
2.71 

4.36 
3-40 
3-6l 

3-3° 
3-9° 
3-47 

S-J° 

3-65 
3-o8 

3-43 
3.00 

3-45 
4.10 
3-6o 

3-63 
4.12 

4-33 
3-45 
2.66 

8.67 

I 

9 

i 

4 
5 
25 
ii 

12 

9 
4 
4 
7 
ii 
16 
ii 
8 
6 

17 

12 
28 
48 
II 
12 
26 
40 

7 

2 

I 

7.00 
7.70 

5-49 
6-57 
7.02 
8.00 

5-55 
7.00 
9.08 

5-5° 
6.94 
7.20 

8.22 
8.23 
12.  OO 
7.70 
6.20 

9.14 
10.82 
10.38 

10.70 
9.00 
9.60 

22.27 
13-93 

11.00 

5 
6 

2 

16 

,i 

2 

8 

17 

I 
5 
5 

12 
15 
13 

6 

i 

34 
ii 
26 

37 
28 

24 
64 
43 
18 

Virginia  and  D.  C.  (since 
1898)    

West  Virginia     .    .    . 

Tennessee   

Missouri      

Ohio 

Indiana 

Illinois 

Michigan         . 

Wisconsin    .    .    . 

Minnesota  

Iowa    ....        ... 

Kansas    

Nebraska    

North  and  South  Dakota 
Colorado 

South  Atlantic  and  Gulf  States 
North  Carolina  ..... 

South  Carolina  

Florida    

Alabama 

Mississippi 

Louisiana    ..... 

Texas  

Arkansas  

Oklahoma  (since  1898)     . 
Pacific  Coast* 

11.50 
7.12 

16 

8 

22.40 
10.40 

33 
24 

California    

Oregon  and  Washington 

The  curves   of    Fig.  12   based  on  the  data  of   Table  No.  7  show 
approximately   the    maximum    rainfalls    which    may   be   expected   for 

*  Since  1894  the  records  are  from  those  stations  having  self-recording  rain  gauges. 


EXTENT   OF  GREAT  RAIN-STORMS.  51 

different  lengths  of  time.  The  curve  for  the  Northern  and  Central 
States  is  somewhat  exceeded  in  a  few  States,  but  for  most  of  them  it 
represents  rainfalls  but  little  greater  than  those  which  have  already  been 
observed,  and  which  may  occur  again  at  any  time.  This  curve  gives 
a  rate  of  4  inches  for  one  hour,  8  inches  for  24  hours,  and  10  inches 
for  48  hours.  The  curve  for  the  South  Atlantic  and  Gulf  States  repre- 
sents the  maximum  recorded  rainfalls  for  all  the  States  of  this  group 
except  Louisiana,  for  which  the  records  far  exceed  those  of  any  other 


12       /6        ao      24-      26      32      36 
Duraf/or?  of  fta/nfa//  //?  Hours. 

FIG.  12. — MAXIMUM  PROBABLE  RAINFALLS. 


-W 


State.  For  the  Pacific  coast  very  high  records  are  also  noted  at  some 
stations.* 

Of  especial  interest  to  the  hydraulic  engineer  are  the  rains  which 
occur  while  the  ground  is  frozen  and  covered  with  snow.  A  study  of 
the  data  shows  that  in  all  those  States  where  such  conditions  could 
obtain,  the  maximum  rates  of  rainfall  for  the  winter  months  are  con- 
siderably below  those  for  the  summer  months.  They  are  approxi- 
mately given  by  the  lower  curve  of  the  diagram.  The  melting  of  snow 
during  an  extensive  rain  may  increase  the  total  equivalent  by  one  or 
two  inches,  thus  giving  about  the  same  total  as  the  summer  curve. 

48.  Extent  of  Great  Rain-storms. —  That  excessive  rainfalls  are  of 
sufficient  extent  to  cover  areas  of  such  size  as  are  ordinarily  considered 
in  water-supply  problems  is  made  evident  by  the  statistics  of  a  few 


*  For  rates  for  shorter  intervals  of  time  than  one  hour  reference  should  be  made 
to  various  works  on  sewer  design  and  to  papers  relating  thereto.  Among  these  see 
references  (6)  to  (TO),  p.  53- 


5 2  THE  RAINFALL. 

great  storms.  In  October,  1869,  a  great  storm  occurred  in  the  eastern 
part  of  the  United  States,  with  its  maximum  intensity  in  Connecticut. 
A  careful  analysis  of  the  records  made  by  Mr.  James  B.  Francis* 
shows  the  areas  covered  by  different  depths  of  rain  to  have  been  as 
follows : 

Depth  of  Rain.  Area  Covered. 

6  inches  or  more ...   24,431  square  miles. 


7 
8 

9 
10 
ii 


9,602 
1,824 
1,046 

519 
179 


The  following  are  some  of  the  maximum  rates  observed  in  this  storm : 

4.00  inches  in    2      hours. 
4.27       "        "     3 
%,.         5.86       "        "   18.5 
7-15       "        "  24 
8.90       "        "  30 
8.44       "        "  42 

The  maximum  recorded  rainfall  was  12.35  inches,  at  Canton,  Conn., 
all  of  which  probably  fell  in  about  48  hours. 

The  winter  storm  in  New  England  of  February,  1886,  was  also' 
very  extensive,  it  being  estimated  that  4  inches  or  more  fell  over  an 
area  of  7600  square  miles,  6  inches  or  more  over  an  area  of  3000  square 
miles,  and  8  inches  or  more  over  an  area  of  750  square  miles,  t  It  is 
probably  true  that  some  of  the  most  violent  storms  of  the  Western 
mountain  region,  the  so-called  "cloud-bursts,"  are  of  much  greater 
intensity  than  any  represented  in  the  table,  but  they  are  very  local  in 
extent. 


LITERATURE. 

1.  Monthly  Weather  Review,  and  other  publications  of  the  Weather  Bureau, 

especially  Bulletin  C,  1894,  and  Bulletin  D,  1897. 

2.  Curtis.     The  Effect  of  Wind  Currents  on  the  Rainfall.     Signal-Service 

Notes  No.  1 6.     Contains  bibliography. 

3.  Francis.     Distribution  of  Rainfall  during  the  Great  Storm  of  October  3 

and  4,  1896.     Trans.  Am.  Soc.  C.  E,,  1878,  vn.  p.  224. 

4.  FitzGerald.     Rainfall :  Does  the  Wind  cause  the  Diminished  Amount  of 

Rain  Collected  in  Elevated  Rain-gauges  ?    Jour.  Assn.  Eng.  Soc., 
1884,  in.  p.  233. 

5.  The  New  England  Rain-storm  of  February  10-14,    1886.     Eng.  News, 

1886,  xv.  p.  2i6f 


*  Trans.  Am.  Soc.  C.  E.,  1878,  vn.  p.  224. 
\  Eng.  News,  1886,  xv.  p.  216. 


LITERATURE.  53 

6.  Weston.     The   Practical    Value    of   Sell-recording    Rain-gauges.     Eng. 

News,  1889,  xxi.  p.  399. 

7.  Rainfall   Observations  at   Philadelphia.     Reports   Phila.  Water  Bureau, 

1890-92.     Eng.  Record,  1891,  xxm.  p.  246;    1892,  xxvi.  p.  360. 

8.  Talbot.      Rates    of    Maximum    Rainfall.      The    Technograph,     1891-92, 

p.  103. 

9.  Self-registering  Rain-gauges  and  their  Use  for  Recording  Excessive  Rain- 

falls.     Eng.  Record',  1891,  xxm.  p.  74. 

10.  Hoxie.     Excessive  Rainfalls  considered  with  Especial  Reference  to  their 

Occurrence  in  Populous  Districts.  "  Trans.  Am.  Soc.   C.  E.,    1891^ 
xxv.  p.  70. 

11.  FitzGerald.     Yield  of  the  Sudbury  River  Watershed   in  the  Freshet  of 

February  10-13,  1886.     Trans.  Am.  Soc.  C.  E.,  1891,  xxv.  p.  253. 

12.  Sherman.     Maximum    Rates    of    Rainfall   at   Boston.    Trans^  Am.  Soc. 

C.  E.  1905,  LIV.  p.  173. 


CHAPTER   V. 
EVAPORATION   AND   PERCOLATION. 

49.  Relation  of  Evaporation  and  Percolation  to  Stream-flow  and  to 
Ground-water. — Of  the  rain  which  falls,  a  part  passes  off  immediately 
into  the  streams  and  forms  what  may  be  called  the  flood-flow ;  a  part 
is  evaporated  directly  from  the  surface  of  the  ground,  from  water- 
surfaces,  and  from  the  leaves  of  vegetation ;  and  a  portion  percolates 
into  the  ground.  Of  the  last  portion  a  part  is  caught  by  vegetation, 
passed  upwards  and  evaporated  or  transpired  from  the  leaves  (an  insig- 
nificant portion  being  retained  by  the  plant),  and  a  part  passes  on 
downwards  and  laterally,  sooner  or  later  finding  its  way  to  the  surface 
again  in  the  form  of  springs,  which  constitute  the  source  of  the  dry- 
weather  flow  of  streams. 

The  total  flow  of  a  stream  is  then,  in  general,  equal  to  the  rainfall 
less  the  evaporation;  the  flood-flow  is  equal  to  the  rainfall  less  the 
percolation  and  evaporation;  and  finally  the  dry- weather  flow  may  be 
considered  as  equal  to  the  deep  or  more  permanent  percolation.  To 
enable  stream-flow  data  to  be  used  in  the  most  intelligent  way  in  mak- 
ing estimates,  it  is  therefore  desirable  to  have  a  knowledge  of  the  laws 
of  evaporation  and  percolation  and  of  the  relative  amounts  which  take 
place  under  different  conditions.  Furthermore,  as  the  percolating 
water  constitutes  the  ground-water  from  which  many  supplies  are 
drawn,  this  knowledge  is  of  first  importance  in  a  study  of  ground-water 
sources. 

The  subject  of  evaporation  naturally  divides  itself  into  two  parts : 
evaporation  from  water-surfaces  and  evaporation  from  land-surfaces. 
The  former  is  of  importance  in  studying  the  run-off  from  watersheds 
having  considerable  areas  of  lakes  and  ponds,  and  in  taking  account  of 
the  evaporation  from  reservoirs.  Considerable  reliable  information 
exists  relating  to  this  part,  and  the  application  thereof  is  easy  and  direct. 
Evaporation  from  land-surfaces  is,  however,  much  more  difficult  to 
determine,  since  the  conditions  affecting  it  are  so  varied  and  indetermi- 

54 


EXPERIMENTS   ON  EVAPORATION  FROM    WATER-SURFACES.    55 

nate ;  it  is  therefore  only  possible  to  give  figures  which  indicate  in  a 
general  way  the  effects  of  some  of  the  conditions. 


EVAPORATION   FROM   WATER-SURFACES. 

50.  Influences  Affecting  Evaporation. — The  evaporation   from  the 
free  surface  of  water  takes  place  at  a  rate  depending  upon  the  tempera- 
ture of  the  water  at  the  surface,  and  upon  the  quantity  of  vapor  already 
in  the  air  immediately  adjacent  to  it.      The  former  varies  not  only  with 
the  air  temperature,  but  with  the  depth,  nature,  and  extent  of  the  body 
of  water,  and  with  the  extent  to  which  it  is  exposed  to  wind  and  sun. 
The  latter  depends  upon  the  amount  of  moisture  in  the  air  generally, 
and  also  to  a  large  extent  upon  the  action  of  wind  in  removing  the 
accumulated  vapor  from  above  the  water.      For  any  given   locality  the 
evaporation  will  vary  closely  with  the  variations  in  mean  air  tempera- 
ture, but  for  different  localities  variations  in  humidity  will  cause  it  to 
be  very  different  even  though  the  temperatures  are  the  same. 

51.  Experiments  on  Evaporation  from  Water-surfaces. — Owing  to  the 
difficulty  of  duplicating  conditions  of  humidity  and  temperature  it  is 
evident  that  determinations  of  evaporation  from  small  shallow  vessels 
are  of  little  use  in  arriving  at  an  estimate  of  the  evaporation  from  large 
bodies  of  water.      The  best  results  have  been  obtained  by  the  use  of 
comparatively  large  vessels  placed  in   a  considerable  body  of  water, 
such  as  a  lake  or  reservoir.      Even  in  this  case  the  variation  in  tem- 
perature between  the  water  outside  and  inside  the  vessel  will  at  times 
be  several  degrees,  and  it  is,  moreover,  difficult  to  eliminate  the  effect 
of  the  sides  of  the  vessel  in  protecting  the  water-surface  from  the  wind. 

52.  Experiments  at  Boston. — The  most  extensive  experiments  of 
this  character  which  have  been  made  in  the  United  States  are  those 
which  were  carried  out  by  Desmond  FitzGerald  at  the  Chestnut  Hill 
reservoir  of  the  Boston  water- works.* 

In  Table  No.  8  are  given  the  mean  monthly  evaporations  as  de- . 
duced  from  these  experiments.      For  the  summer  months  they  are  the 
means  for  ten  years  of  observations,  while  for  the  winter  months  they 
are  deduced  from  special  experiments  on  the  evaporation  from  snow 
and  ice. 

The  maximum  daily  evaporation  was  0.57  inch,  the  mean  tempera- 
ture of  the  water  being  70°.  7  F.  in  the  reservoir  and  68°.  8  in  the  tank. 
Experiments  on  snow  and  ice  indicated  an  evaporation  of  about  0.02 

*See  references  (2)  and  (5),  p.  65. 


EVAPORATION  AND   PERCOLATION. 


inch  per  day  from  snow  and  0.04  inch  from  ice.  The  maximum  yearly 
evaporation  was  43.63  inches  and  the  minimum  34.05,  or  a  variation 
of  1 1  per  cent  above  and  13  per  cent  below  the  mean. 

TABLE    NO.    8. 

MEAN   MONTHLY    EVAPORATIONS    AT    CHESTNUT    HILL    RESERVOIR,    BOSTON,    MASS. 


Month. 

Evaporation, 
Inches. 

Per  cent  of 
Yearly 
Evaporation. 

Month. 

Evaporation, 
Inches. 

Per  cent  of 
Yearly 
Evaporation. 

15-2 
14-0 
10-4 

8.1 
5-7 
3-9 

0.96 
1.05 
1-70 
2.97 
4.46 
5-54 

2.4 

2.7 
4-3 
7-6 
11.4 
14.2 

Tulv    . 

5.98 
5-50 
4-T2 

3-i6 

2    25 

1.51 

March           

Anril 

October 

November  

Total  for  the  year  =  39.20  inches.         Mean  temperature  =  48°. 6. 

53.  Experiments  at  Rochester. — A  similar  series  of  experiments 
have  been  carried  on  since  1891  by  Mr.  Kuichling  at  the  Mt.  Hope 
reservoir  of  the  Rochester  water-works. *  The  results  of  these  experi- 
ments are  given  in  Table  No.  9.  They  are  the  means  of  observations 
covering  from  two  to  eight  years. 

TABLE   NO.  9. 

MEAN  MONTHLY  EVAPORATIONS  AT  MOUNT  HOPE  RESERVOIR,  ROCHESTER,  N.  Y. 


Month. 

Evaporation, 
Inches. 

Per  cent  of 
Yearly 
Evaporation. 

Month. 

Evaporation. 
Inches. 

Per  cent  of 
Yearly 
Evaporation. 

O    ^2 

I    e 

Tulv 

c    47 

is  8 

O    ^4. 

I    6 

August  

S-IQ 

T  e    A 

March  

I    H 

a   Q 

September  

A      1C 

12    O 

2    62 

7.6 

October  

q  16 

91 

May  

0      Q-l 

II  .4. 

November  

I    A.*! 

'A  .2 

4QJ. 

id.  ^ 

I    11 

32 

Total  for  the  year  =  34.54  inches.         Mean  temperature  =  47°. 8. 

54.  Other  Experiments. — Experiments  by  J.  J.  R.  Croes  on  the 
Croton  River  in  1865—1870  for  eight  to  ten  months  of  the  year  gave, 
as  filled  out  by  Mr.  FitzGerald  t  for  the  winter  months,  an  average 
annual  evaporation  of  39.64  inches. 

Of  foreign  experiments,  those  made  by  Mr.  Charles  Greaves  at  Lee 
Bridge,  England,  are  probably  the  most  extensive. %  They  embrace 
fourteen  years  of  observations,  and  were  carried  out  by  means  of  a 

*  See  the  various  annual  reports  of  the  Executive  Board  of  Rochester,  N.  Y« 
f  Trans.  Am.  Soc.  C.  E.,  1886,  xv.  p.  617. 
\  Proc.  Inst.  C.  E.,  XLV.  p.  19. 


CA  LCULA  TED    E  VAPOR  A  TIONS. 


57 


floating  slate  tank,  3  feet  square  and  12  inches  deep,  placed  in  the  river 
Lee.  The  results  are  given  in  Table  No.  10.  The  maximum  yearly 
evaporation  was  26.933  inches  and  the  minimum  17.332,  the  variations 
being  31  per  cent  above  and  16  per  cent  below  the  mean. 

TABLE  NO.  10. 

MEAN    MONTHLY    EVAPORATIONS    AT   LEE   BRIDGE,    ENGLAND. 


Month. 

Evaporation, 
Inches. 

Per  cent  of 
Yearly 
Evaporation. 

Month. 

Evaporation, 
Inches. 

Per  cent  of 

Yearly 
Evaporation. 

Once 

•3     6 

Tulv 

3/1/1  "3 

16  7 

O.6O3 

2.Q 

2.84Q 

n  8 

1  .  065 

52 

September  ........ 

I     606 

7    8 

2    Oo8 

JO    2 

October  

I     O^6 

51 

May 

2.  7^ 

jq    A 

O.66Q 

30 

Tune  

•2  .  14.2 

1C.    2 

December  

O.  574. 

2.8 

Total  for  the  year  =  20.613  inches. 

55.  Calculated  Evaporations  from  Water-surfaces. — In  Table  No.  1 1 
are  given  calculated   evaporations   deduced  from  readings  of  dry-  and 
wet-bulb  thermometers  at  various  Signal  Service  stations  in  1887  and 
1888,  supplemented  and  controlled  by  observations  at  several  stations 
by  means  of  the  Piche  evaprometer.*     The  results  indicate  at  least  the 
relative  conditions  of  temperature  and  humidity  at  the  various  stations, 
and    are  therefore    indicative  of  the   relative  evaporation.      They  are 
believed  by  Mr.  Russell,  the  officer  in  charge,  to  represent  approxi- 
mately the  evaporation  from  surfaces  of  ponds,  lakes,  and  reservoirs. 
The  results  thus  obtained  for  Boston,  New  York,  and  Rochester  agree 
quite  well  with  the  observations  already  quoted. 

PERCOLATION,    AND   EVAPORATION   FROM    LAND-SURFACES. 

56.  Influences  Affecting  Evaporation  and  Percolation. — Evaporation 
from  the  ground  depends  upon  the  moisture  contained  therein,  upon 
the  temperature,  and  upon  the  nature  of  the  vegetation  or  other  soil- 
covering.     The  moisture  present  in  the  ground  depends  in  turn  upon 
the  rainfall,  and  the  ability  of  the  soil  to  receive  and  retain  the  perco- 
lating water.     The  greater  the  rainfall  the  greater  the  evaporation,  but 
evaporation  is   relatively  much  more   constant   than   the  rainfall.      It 
therefore  follows  that  the  difference,  or  the   stream-flow,  is   more  vari- 
able than  either,  and  as  the  rainfall  increases  the  percentage  flowing 
off  will  increase. 


*  Monthly  Weather  Review,  Sept.  1888,  p.  135. 


EVAPORATION  AND    PERCOLATION. 
TABLE    NO.   11. 

CALCULATED    MONTHLY    EVAPORATION    IN   THE   UNITED    STATES. 


Stations  and  Districts. 


New  England: 

Eastport 

Portland 

Manchester 

Northfield 

Boston 

Nantucket 

Wood's  Holl 

Block  Island 

New  Haven 

New  London 

Middle  Atlantic  States: 

Albany 

New  York  City 

Philadelphia 

Atlantic  City 

Baltimore 

Washington  City-... 

Lynchburg 

Norfolk 

South  Atlantic  States: 

Charlotte 

Hatteras 

Raleigh 

Wilmington 

Charleston 

Columbia 

Augusta. 

Savannah 

Jacksonville 

Florida  Peninsula: 

Titusville 

Cedar  Keys 

Key  West 

Eastern  Gulf  States:. 

Atlanta 

Pensacola  

Mobile 

Montgomery 

Vicksburg 

New  Orleans 

Western  Gulf  States: 

Shreveport 

Fort  Smith 

Little  Rock 

Corpus  Christi 

Galveston 

Palestine 

San  Antonio 


0.9 
i.o 
0.9 
0.8 

1.2 
I.I 
0.5 
I.  I 
I  .  I 


0.9 
1.8 
1.6 

1.2 
2.0 

1.8 

2.6 

1.8 

2.6 
1.8 

2.0 
2.4 

2-5 
2-2 
3-0 

3-3 
2.9 


3-5 
3-3 
3-8 

2-7 
2.9 

2.6 

3.5 

2.1 

2.8 

1.6 

2.2 
2.1 
1.4 
1.6 
2.1 
2.4 


1.4 
1.2 

.6 
.o 
.6 
.1 
0.8 
.1 
.6 
-3 

.2 

•4 
2.  I 

1.6 

2.2 

i-7 

2.7 

1.6 

2.6 
1.6 

1.8 

2.2 
2-5 
2-3 
2.6 
2.8 
2.6 

2.6 

2.8 

3-7 

2.6 
2.8 

2.5 

3-3 

2-5 
2.8 

2.1 

2-7 
2.8 

1.6 

2.8 

3.0 

3-3 


rt  °2 

2 


1-5 
1.8 
2.2 

2.2 
.2 

.8 

.2 

.8 
•5 

1.6 

2.0 
2.5 

1.5 

2.S 
2.5 

3-4 

2-3 

4-3 
1.6 
2.6 

2.7 
3-5 
2.6 

3-4 
4-i 

3-8 

3-3 
4.0 

3-8 

4.0 
4.1 
2.8 
5-1 
3-6 
4.1 

3-o 
3-5 
3-5 
3-3 
3-2 
3-3 
4.1 


2.4 

2.6 

3-3 

2-3 

3-4 

i 

2.4 

2.0 

2.7 

2.6 

3-3 
3-4 
4.4 
2.4 
5-1 
4.2 

5-2 

3.5 

6.4 
2.5 
3-8 
3-3 
3-7 
4.8 

5.3 
4-7 
4-3 

3-8 
4.6 
4-5 

6.2 
4.0 
3-5 
6.5 
5-1 
3-8 

4.8 
5-3 
5.5 
3-o 
2.9 
4.2 
3-8 


2-5 
1.8 
3.8 
2.5 
3-1 
1.8 
1.8 
1.8 
2-7 

2.8 

3.9 

3-3 
4.0 
1.8 
4-7 
3-8 
4-5 
3-2 

4-5 

2.2 
4.1 

3-3 
3-9 

4.3 

4.8 

4-3 
4.6 

3.8 
4-5 
4-4 

4-7 
4-3 
3-7 
5-9 
5-7 
4.2 

4.9 
4.4 
4.8 
3-2 
4-3 
4-3 
4.0 


2.7 

3-3 

5 

3-4 

4-7 

2.  I 
2-7 
2.6 

4.1 
4.0 

4-5 
4.6 


5.6 
6.0 
5-6 
4.2 


5-4 
4-3 
4.4 

5-4 
5-0 
4.6 

5-3 

4-3 
5-i 

4.8 


4-6 
4.0 

5-8 
4.8 
4.1 

4.2 
4.6 
4.1 

3-9 
4.2 

4-5 
4-5 


2.2 

3-8 
4-1 

3-5 
4.4 

3.3 
2.7 

2.5 

3-7 
3.4 

5-0 
5-0 
5-7 
2.9 
6.0 
5-4 
4-7 
4-6 

4.0 

3-3 

4.2 


4-3 
4-5 
4.2 
4.8 
4.2 
5-0 

3-8 
5-o 
5-1 


5-0    4-5 


5-0 
4.1 

4-3 
4.0 
4.1 

4-9 
5.6 
5-4 
4.4 

5-3 


6.6 


2.9 

3-3 
2.7 
4.0 
3-8 
2.4 
3-1 
3-8 
3-9 

4-7 
5-2 
5-2 
3-3 
5-0 
4-9 
4-3 
3-7 

4.0 
4-i 
3-2 

4^8 
3-8 
4-5 
4-7 
4-7 

4-3 

5-5 


4-7 
5-4 
4.6 

4-5 


5-2 
4.6 
5-9 
4-3 

5.2 
4.6 

5-8 


2-5 
3-4 
2.5 
2-3 
3-5 
3-4 
2.7 
2.8 
3-1 
3-2 

3-2 
4.3 
4 
2.4 

4-4 
4.1 

3-3 


4.6 
3.8 
3-0 

3-9 
4.2 
4.2 
5-1 
3-4 
3 

4.0 

4-5 
4.7 

5-8 
5-2 
4.6 
5-7 
4-7 
4.4 

5-0 
4-7 
5-8 
4-3 
5-2 
4.8 
5-2 


3^ 
2% 

<r 


2.6 

3.0 


2. 
I. 

2.7 
2.7 
1.2 
2.6 
3-2 


3-o 
.4.1 
4.0 
i 

4-3 
4.2 

3-4 

2 

4.0 
3-2 
2-7 
3-4 
4.0 

3-4 
4.1 
3-6 
3-6 

4.1 
4.1 
4-3 

4.6 

4-5 
4.1 
4.6 

3-4 
4.6 

4.1 

5-9 
5-2 
4.1 
4-7 
4-4 
5-4 


2.2 

2-5 
2.4 
I.I 
2.2 
1.8 
O. 

1.8 
2.4 
2-4 

2.  I 
3-3 
3-3 
1.2 

3-6 

4-5 
3-2 
2-3 

3-6 
2.6 
2.4 

2.8 

3.2 

3.6 
3-6 
3-5 
3-0 

3-6 
3-5 
3- 

4.2 
3-6 
3-4 
4-3 
4.0 

3-7 

3-4 
3-9 
4-3 
3-0 
4.2 
4.0 
4.2 


Jgg 


.425.2 
.4:29.7 
.433.3 

.OJ23-9 
•434-4 
.8125.6 
0.520.3 
.424.0 
.631.8 

2.1  31.8 

1.434-8 
2.240.6 
2.2J45.0 
1.5125.2 

2.448.1 
2-545.6 
2.645.5 
1.835.6 

2.649.0 
1-631.3 
1.837.0 
2.738.4 
2.543-7 
2-443-2 

3-i  49-3 
2.8  46.0 
2.145.7 

3-144-2 
2.649.5 
3-6  51-6 

2-551-5 

2.2  42.1 


3-1 


56.6 


2.247.1 
2.545-4 

45-6 
49-6 

51-7 
38.8 


2.4 

2.2 
2-3 
2-3 

2 . 4  46 .  o 

2.IJ47-I 
3.IJ52.4 


CA  LCULA  TED    E  VA  FOR  A  TIONS. 


59 


TABLE    NO.   \l,— Continued. 

CALCULATED   MONTHLY   EVAPORATION   IN   THE   UNITED   STATES. 


Stations  and  Districts. 

1 

c 
n 
H-  > 

jS 
1 

rf    * 
<->  oo 

a™ 

fl 

< 

ll 

.00 

c°° 
3 
i—, 

x£ 

3   M 
i  —  > 

1  ^ 

taoo 
< 

r  ^~ 

a°° 

cJ5 

October, 

1887. 

_.  t^ 

§1 

J5 

JS 

8" 

1 

Rio  Grande  Valley  : 
Rio  Grande  City  
Brownsville  
Ohio  Valley   and   Ten- 
nessee: 
Chattanooga  
Knoxville  
Memphis  

2.7 

1.8 

2.O 
2.4 
2.1 

i.q 

3-5 

2.6 

3-3 

2.6 

2.3 

2.1 

3-5 
2.9 

3-3 
3-4 
3-i 

•7.2 

3.6 
3-0 

5-3 
5-0 
5-9 

C.Q 

4-5 
3-5 

3-7 
3-5 
5-3 

e  o 

4.6 
3-9 

4-3 
4.2 

4.8 

C.I 

6.9 
4.0 

4-3 
4-9 
4.9 

5-5 

7-0 
4.1 

5-0 
5.o 
5-4 
6.-?. 

5-2 
3-3 

5-4 
4-9 
5-5 
5.0 

4-9 
3-0 

4.0 
4.1 

4.2 

4.O 

3.6 

2.6 

3-9 
3.8 
4.1 

a  a 

3.1 

2.3 

1,9 

2.1 
2.4 
I.Q 

53-1 
37-c 

46.4 
45-  c 
5o.c 
50.  i 

Louisville           

1.7 

2   I 

2  8 

e  6 

5  A 

*  8 

6.8 

7  J. 

6  4 

4Q 

q  8 

2  I 

e;i  f 

Indianapolis  
Cincinnati  

1.3 

1.8 
1.6 

1.4 

1.8 

2  O 

2.2 
2.6 
2  1 

4.6 
4-9 

A   e 

4.8 

5-2 

4  8 

5.7 
6.4 
«5  8 

7-7 
6-5 
6  n 

6.9 

6.6 

6.4 

5.2 

6.1 

c.  i 

4.1 

4-7 

4.  O 

3-1 

3-3 

2.6 

1.6 
2.1 

i  8 

4s.e 

52  C 

17  f 

Pittsburg  
Lower  Lake  Region  : 
Buffalo           

1.4 
o  8 

I.Q 
j   j 

2.2 
I   ^ 

3.8 

2  2 

4.2 

30 

5-4 

3Q 

6.6 

4Q 

5-6 

52 

4.9 

3Q 

3-4 

2  8 

2.8 
I  Q 

2.3 
I  6 

44-! 

•?2  C 

Oswego  
Rochester  
Erie  

0.6 

o-5 

I  O 

1.0 
I.I 
I  4 

I.I 

0-9 
i  4 

2.2 
2.6 

27 

2.8 

3-8 

37 

3-8 
4.9 

4  6 

3-9 

4.6 

c.e 

4.0 

4-1 

4  8 

3-6 

3-8 

a   i 

2.7 

2.6 

2   t? 

2.2 
2.2 
I  Q 

I.O 

1-3 

I   2 

28.  c 

32.^ 

TT  ? 

1.  1 

I  A 

T   e 

2  Q 

30 

41 

c.2 

4Q 

T.8 

3     A 

2  4 

I  4 

qe  •• 

Sandusky  
Toledo  

0.8 

O.Q 

1.4 
I   I 

1-5 
I   e 

3-2 

q  e 

3-7 
•a.  8 

4.6 

A  6 

5.4 

6.0 

5.4 

6.4 

3-7 
•7  7 

3-4 

•7  4 

2.2 

2.4 

1-3 
I.q 

36.f 
?R  f 

o  8 

j    j 

I  6 

•3  o 

4.  T 

4  8 

5.Q 

c,2 

•7.4. 

2.8 

2.O 

I.q 

q6  r 

Upper  Lake  Region  : 
Alpena  
Grand  Haven  
Lansing  
Marquette  
Port  Huron  

0.7 
0.5 

0.6 
0.8 
0.6 

I  O 

0.6 
o.7 

1.2 

0.8 

I.O 

0.9 
•  3 
•4 
0.9 
.1 
3 

1.6 

2.6 

2.7 

1.7 

2.6 
32 

2.1 

3-i 

2.8 

2.4 

3-0 

30 

3-6 
3-8 
4.0 
3-3 

3-8 

4  8 

3.8 
4-7 
4-3 
3-4 
4.6 

5     A 

3.7 

3.8 
3-9 
3-3 
4-2 

5q 

2.8 

2-7 
2.4 
3-1 
3-2 
41 

2.2 

2.6 
1.9 
2.2 

2-5 
32 

1-5 
1-7 

1.4 
1.3 

i-7 

2  ^ 

0.8 
i.i 

I.O 

1.3 

I.O 
I   2 

24-: 

28.( 

27  e 
24.  J 
29.: 

q6  f 

O  5 

I  O 

.i 

2  4 

2.6 

r8 

<\  8 

•7  7 

3.4 

2.9 

I.Q 

O.9 

29.  c 

Green  Bay  

Duluth    ... 

0.5 

Oc 

0.6 

o  ^ 

0.8 
o  6 

1-7 

T      C 

2.5 

24 

4.1 

2e 

5-6 

3Q 

4.2 

3      A 

3-0 

•7    O 

2.4 
2.5 

1.9 
1.2 

0.9 
I.O 

28.  i 

2q.( 

Extreme  Northwest  : 
Moorhead  

O,2 
O  ^ 

1.4 

Oq 

0.5 

O  ^ 

2.1 

i  8 

3-6 

q  8 

3.8 

3Q 

3-7 

a   1 

3-  .3 

2  6 

3-5 

2  6 

2.4 
2.O 

1-3 

O.Q 

0.5 

o  •* 

26.: 
22.  1 

Bismark  
Fort  Buford  

0.4 
1.4 

O  2 

0.6 
0.7 

o  ^ 

0.6 
0.6 

O.4 

3-0 
3-0 

2  2 

4-3 
4-7 

4  6 

4.1 
5-0 

•2.8 

5-6 

6.2 
4  2 

4.2 

4-9 

37 

4.0 

4.8 
a.  7 

2.6 

3-0 
2.3 

1.2 

1-7 

1.4 

0.4 
0.5 

0.4 

31.  < 

35-! 
27.2 

Upper  Mississippi  Val- 
ley: 
Saint  Paul  
La.  Crosse  

0.7 

O  A 

0.7 

2 

2.2 
I  4 

2.0 

30 

2.3 

3c 

4.1 

41 

5-0 

5       A 

3-7 

47 

2.8 
30 

2.4 
30 

i.5 
1.8 

0.7 

0.8 

28.1 
•32.  c 

Davenport   

O  ^ 

o 

i  8 

o  R 

3  A 

4  6 

6  o 

6  2 

44 

30 

2.7 

i.i 

qq.c 

Des  Moines  

0.6 

07 

.O 
O 

1-5 

3.7 

3-1 

2  O 

4-2 

6.6 

6  2 

4-7 
4  8 

4.1 

3-3 
2  8 

2-3 

i  8 

0.9 

O  Q 

36  c 

Oq  J 

Keokuk  

0.8 

.1 

2.1 

4.2 

z.y 

•7.7 

4-7 

7  O 

4-° 
6  8 

c.  o 

•3.8 

2.Q 

1.2 

42.  c 

Cairo  

i  6 

J 

2Q 

e   S 

44 

40 

e  6 

6  «; 

e   T 

4    ^ 

1  8 

2.q 

18  r 

Springfield    111.... 

o  8 

I 

2  O 

4  6 

q  8 

4  ^ 

5      A 

6  s 

4c 

3C 

2  Q 

1.4 

^|0  ? 

St.  Louis  

1-3 

.6 

2-5 

5.5 

4-7 

5.o 

7-5 

8.0 

5.9 

4.9 

3-9 

1.4 

52.i 

6o 


EVAPORATION  AND   PERCOLATION. 


TABLE    NO.  11.— Continued. 

CALCULATED   MONTHLY   EVAPORATION   IN   THE    UNITED   STATES. 


Stations  and  Districts. 

! 

| 

4% 

'EJ2 

di 

«s 

£ffi 

i§ 

*Jog 

k 

i 

>r£ 

rf£ 

V? 

A 

fe 

2, 

< 

s 

i—  > 

V) 

0 

i 

Q 

> 

Missouri  Valley  : 

i.i 
i.i 
0.9 

i.i 

0.8 
0-7 

1.2 

0.6 

0.3 

0.4 

0.8 
0.6 
i.i 
i.i 
0.4 

3-3 
0.8 

3-o 

2.8 
2.1 

1-3 
i-4 
1-3 

1.6 

1.8 
5-4 
3-9 

4.0 
3-0 

2.6 

5-2 
1.4 
4.4 
3-0 

0.8 
0.9 
1.8 
1.8 
1.6 

1.6 
0.7 
I.i 

1.6 
1-5 

1.2 
1-5 
I.I 

1.6 
0.9 
0.7 
1.4 

1.2 

1-5 
1.4 
3-6 
0.8 

5.7 
1.8 

3-3 
3-7 
1-3 

2.8 

2.4 
1.9 

2.0 
1-7 

5-7 
3-9 

3-9 
3-4 

2^8 

5.2 

4.6 

1.8 

2.8 

2-7 

2.7 

2.5 
2.5 
2-9 

2.4 
2.4 
2.3 

2.0 
1.4 
1.2 

1.8 

i-3 

6.8 

1.2 

1.2 

1-3 
I.I 

2.1 

0.8 

4.0 

1.8 

4.1 

3-5 
1-5 
i.S 

2.8 

3-2 

2.6 

6-7 

5.2 

6.0 
4.2 
3.6 
6-4 
3-6 
6.6 

6-3 
1.8 

6.2 

3-6 
3-7 
2.7 

3.8 
2.7 
3-6 

4.4 
5-0 
4.6 
4.0 
4-4 
3-5 
5-0 
44 
3-7 
3-3 

3-8 
5-4 
3-3 
6.1 
2.7 

8.2 

5-4 

6.7 
7-6 

2.1 

4.8 
4.1 

3-8 
4.2 

8.5 
7-3 

8.4 
6.8 
6.8 
9.2 

5-4 
9.6 

8.7 

4.6 
9.1 

7-2 

6.2 

4.3 

6.1 

4-4 

6.2 

3-8 
4-8 
4-5 
4.1 
3-8 
3-3 
3-2 
4.1 
3-7 

4-1 
6.8 
3-2 
4-3 
4.9 

5-2 

3-9 

5-6 
5-8 
1.8 

4-3 
4.6 

5-4 

4.0 

5-0 

II.  0 

9-5 

10.7 
8.8 
9-4 

10.2 
6.2 

9.6 
9-3 

5-2 
9-3 
6.9 
7.0 
4-3 

6.5 
5-4 

7-7 

4.0 

4-0 
5-0 
4.1 
5-2 
4-5 
5-3 
5-2 
4.1 
4-4 

4.2 
4-9 
4.6 
5-5 
5.7 
10.4 
6.9 

4-3 
10.5 
1.9 

5-7 
7-4 

8.2 

4.4 

5-8 

12.0 
IO.9 

136 
12.9 
9.1 

13-8 

8.1 
11.9 
4.0 

IO.I 

8.9 
ii.  i 

6.5 

6.6 
4.4 

5.7 

6.0 
5-0 
6-3 
6-3 

6.2 

5-6 
6.9 

7-7 
5-7 
4.6 

6.S 
9.6 
6.8 

7-2 

6.0 

8.0 
6.0 

6.7 
8.3 
3-0 
7-3 
8..? 
7.6 

4.8 
9-5 
11,4 
9.4 

9.4 

9-2 
7-1 
12.4 
6.6 

12^8 

8.8 

11.5 
9.2 

10.2 

7-7 

IO.O 

7.7 
9.9 

4.6 
3-4 
4-5 
3-5 
5.2 
4-7 

4.9 

4-2 

3.7 

5-5 
8.0 
4.6 

7-7 
4.8 
7-7 
4-8 

7-2 

8.5 
4.0 

5-2 

6.6 

6.2 

7-5 
7-5 
9.0 
ii.  6 

7-7 
9.8 

6.7 
10.5 
6.5 

TO.  2 
13-9 

8.1 

12.0 
10.7 

8-3 

6.8 

9-2 

6.4 
7-9 

3-7 

3-4 
4.0 

4-3 

% 

4.1 
2.9 

4.8 
6.1 

i;< 

4-4 
8.6 

3-7 

6.8 
6.1 
3-0 

4-3 
5  5 
5.4 

6.2 

5.9 
3-9 

5.6 
6.6 

5-3 
9.0 

4-7 

8.2 

10.6 

5-0 
9.9 
9.6 
6.9 
5-6 

7.4 
3.8 
5-1 

3-6 

3-5 
3-9 
1  3-0 
|  4-3 
J3-6 

|3-8 
3-6 

3-1 
3-0 

3-5 
3.4 

2.8 

43 

2-5 
5-8 

2.8 

4.6 
4-9 
2.3 
4-5 

5-2 
4-7 

4.2 

4-5 

5-2 

4.0 

5.2 
6.7 

5-2 

7-9 
4-9 

8.2 

8.8 

4.6 
6.6 
6.5 
5-2 
4.2 

5-2 
2-5 
3-4 

2.9 
2.7 

2.2 

3-0 
2.4 
3-3 
2.8 
2.4 
2.2 

2-5 
2-9 
2.0 

3-o 
1.7 
6.1 

2-3 

4.2 
4.2 

2.8 

3.4 
4.2 
42 

4.1 
3.4 

5.7 
36 

4.6 
5-7 
4-1 
7-2 
3-6 

5-9 

2.4 

3-7 
5-0 
3-4 

5-2 

3-2 

1.7 

1.8 

1.5 

1.4 

1.4 
1.4 
I.I 
1-5 
0.7 
0.7 
0.8 

i.i 
1.5 
i.i 

2.1 
0.7 

3.5 
I.I 

2-9 

3.1 

I.O 

1.8 

2.1 
2.2 

2.O 
1-7 

4-9 
3-8 

2.9 

2.7 

2.6 

4.6 

2.2 

4.6 

4.8 

1.3 

1.8 

2-3 

2.O 

4-7 

1.8 
1.4 
2.4 

39-6 

38-3 
41.6 
36.1 
41.7 
35-5 
43-8 
41.9 
33-0 
31.0 

39-5 
52.0 

35-8 
53.4 
35-4 
76.5 
4L3 

59-4 
69.0 
26.8 
47-2 
54.6 
55-4 

46.1 

54-4 
91.4 
76.0 

82.0 
79.8 
65-5 

IOI.2 
56.0 

95-7 
100.6 

48.9 
83.9 
74-4 
68.3 
56.1 

63-9 

42.8 

57-7 

Springfield    Mo  ..... 

Leavenworth  

Omaha  
Crete  

Valentine  
Fort  Sully      

Huron  
Yankton  

Northern  Slope  : 
Fort  Assiniboine.  .  .  . 
Fort  Custer       

Fort  Maginnis  
Helena  

Poplar  River  
Cheyenne  
North  Platte  
Middle  Slope: 
Colorado  Springs..  .  . 

Pike's  Peak  

Fort  Elliot 

Southern  Slope: 
Fort  Sill  
Abilene   

Fort  Davis  
Fort  Stanton  
Southern  Plateau  : 
El  Paso  

Santa  Fe  

Fort  Apache  
Fort  Grant 

Prescott  
Yuma  
Keeler  

Middle  Plateau  : 
Fort  Bidwell  

Salt  Lake  City  

Northern  Plateau: 
Boise  City  

Spokane  Falls  

Walla  Walla  

EFFECT  OF   VEGETAl^ION  OR   CTHER   SOIL-COVERING. 


6l 


TABLE    NO.   11.— Continued. 

CALCULATED    MONTHLY    EVAPORATION    IN    THE    UNITED    STATES. 


Stations  and  Districts. 

00 

r 
c 

°2 

"cl 

& 

•«• 

D    *"** 

b£oo 

Jo? 

C  oo" 

t»'oo 

•  OO 

uoo 

8 

rt 

H-  > 

fe 

s 

< 

< 

(A 

0 

S5 

Q 

V 

North  Pacific  Coast: 

Fort  Canby  

1.2 

.1 

.8 

2.1 

2.8 

2-3 

1.8 

2.9 

1.8 

1.8 

•  5 

0.9 

21.  1 

Olympia  

1.3 

.2 

.8 

2-5 

4.1 

3-3 

3-2 

2.4 

i  .5 

•3 

.1 

26.8 

Port  Angeles  

I  .O 

0.9 

.8 

1.8 

2-5 

2.1 

2.1 

i.'s 

i-5 

1  .2 

L    -3 

.  I 

I9.I 

Tatoosh  Island  

1  .2 

.  I 

.8 

1.4 

1.8 

1.8 

I    4 

I    4 

I    4 

I   6 

8 

TR   I 

Astoria  

I.I 

.O 

.6 

2.1 

2.7 

3-o 

2.9 

2.6 

2-3 

.8 

.2 

25-3 

O.Q 

.  I 

2   4 

•3.4 

c    o 

3-  2 

4   2 

•2.4 

2.  7 

.8 

.  2 

'3,4.7 

Roseburg  

u  .  y 
1.2 

.6 

-  »  -4 
2.7 

J  f» 
3-9 

D  •  w 

4-7 

3.5 

5-4 

-4  •  ^ 

4-7 

O  •  *T 

5-o 

•*  / 

3-2 

•  7 

.6 

j*+  •  / 

39-2 

Middle  Pacific  Coast: 

Red  Bluff  

3-0 

4-6 

5-4 

6.1 

7.0 

6.9 

II.  O 

10.7 

IO.  I 

10.5 

5-9 

3.6 

84.8 

Sacramento  

1.8 

3-1 

3-7 

4-3 

4.2 

5-6 

5-9 

5.6 

6-5 

7.3 

3-9 

2-4 

54-3 

San  Francisco  

2.7 

2.7 

3-3 

3-1 

2.8 

3-  l 

2.4 

2.5 

3-3 

5-o 

2.8 

3.0 

36.7 

South  Pacific  Coast: 

Fresno  

1.8 

2.8 

3-0 

5-6 

6.0 

7.0 

9.1 

10.2 

7.6 

6.7 

3-8 

2.2 

65.8 

Los  Angeles  

2.3 

2.0 

2.8 

3-4 

3  -O 

3-8 

3-2 

3-5 

3.  i 

4.1 

3-0 

3-0 

37-2 

San  Diego  

2-9 

2.7 

2-5 

2-7 

3-3 

2.8 

3-2 

3-3 

2.9 

4-3 

3-2 

3-7 

37-5 

If  the  soil  is  very  coarse  or  sandy,  percolation  will  be  rapid  and 
large,  and  the  water  will  soon  escape  beyond  the  reach  of  vegetation. 
This  will  result  in  a  small  evaporation,  a  large  percolation,  and  conse- 
quently a  large  and  steady  stream-flow.  If  the  soil  is  very  fine,  or  is 
hard  and  impervious,  both  percolation  and  evaporation  will  be  small  and 
stream-flow  large  and  irregular.  Topography  also  greatly  affects 
evaporation  by  affecting  percolation.  The  maximum  evaporation  will 
occur  where  the  soil  is  sufficiently  porous  and  level  to  receive  the  water 
and  to  retain  it  within  the  reach  of  vegetation. 

57.  Effect  of  Vegetation  or  Other  Soil-covering. — As  showing  the  in- 
fluence of  vegetation  on  evaporation,  Risler's  widely  quoted  table  of 
the  daily  consumption  of  water  by  various  crops  during  the  growing 
season  is  here  given : 

r,_  Consumption  of  Water 

Crop'  in  Inches  per  Day. 

Meadow-grass 0.134  to  0.267 

Oats 0.140  "  0.193 

Indian  corn.    o.no  "  0.157 

Clover 0.140  "   

Vineyard f 0.035  "  0.031 

Wheat 0.106  •'  o.uo 

Rye 0.091  "   

Potatoes 0.038  ' '  0.055 

Oak  trees 0.038  "  0.035 

Fir  trees 0.020  "  0.043 

These  figures  indicate  that  the  grain  crops  will  consume  from  IO  to 
15  inches  of  water  during  the  growing  season.  Grasses  require  still 
more  per  day,  and  for  an  entire  summer  season  will  consume  30  or  40 


62  EVAPORATION  AND   PERCOLATION. 

inches,  if  furnished.  Baldwin  Latham  found  that  Italian  rye-grass 
would  under  suitable  conditions  consume  from  100  to  200  inches  per 
year,  if  supplied.* 

From  this  it  is  seen  that  the  demands  of  vegetation  during  the 
growing  season  are  very  great,  and  until  these  are  satisfied  very  little 
is  left  to  replenish  the  ground-water  or  to  add  to  stream-flow.  The 
large  amount  consumed  by  grasses  and  grains  as  compared  to  forest 
trees  is  to  be  noted.  Other  experiments  indicate  less  difference  in 
favor  of  forest  trees,  but  there  is  little  doubt  that  forests  require  less 
water  than  crops.  Fernow  gives  as  the  ratios  of  the  evaporation  from 
different  surfaces  relative  to  that  from  a  water-surface  the  following : 
sod  1.92;  cereals  1.73;  forest  1.51;  mixed  1.44;  water  i.oo;  bare 
soil  o.6o.t  Forests  not  only  consume  less  water  than  crops,  but,  what 
is  of  more  importance,  they  promote  regularity  of  stream-flow  by 
retarding  the  surface-flow  and  so  increasing  the  percolation  as  well  as 
delaying  and  decreasing  the  flood-flow. 

The  effect  of  a  covering  on  the  ground-surface  is  shown  by  experi- 
ments of  Eser.  Calling  the  evaporation  from  bare  ground  100  per 
cent,  the  evaporation  from  ground  covered  with  I  cm.  of  sand  was 
33  per  cent;  when  covered  with  5  cm.  of  straw  10  per  cent;  with 
5  cm.  of  forest  leaves  from  n  to  15  per  cent;  and  with  grass  growing 
thereon  243  per  cent.it 

The  effect  of  vegetation,  or  other  covering,  upon  the  percolation  is 
of  course  the  reverse  of  its  effect  upon  evaporation.  Experiments  by 
Wollny  on  bare  soils  20  inches  deep  showed  that  for  six  months,  May 
to  October,  the  percolation  was,  for  sand  65  per  cent,  for  loam  33  per 
cent,  and  for  peat  44  per  cent  of  the  rainfall.  With  grass  growing 
thereon  the  percolation  was  14.0,  1.3,  and  8.7  per  cent,  respectively, 
nearly  all  of  which  occurred  in  October.  § 

58.  Experiments  on  Evaporation  and  Percolation. — Greaves  carried 
out  in  connection  with  his  experiments  quoted  on  page  57  many  experi- 
ments on  soils.  Two  slate  tanks  were  filled,  one  with  ordinary  soil 
and  sodded  over,  the  other  with  fine  sand.  All  the  rai;i  either  evap- 
orated, or  percolated  through  the  soil.  The  average  results  for 
fourteen  years  were  as  follows: 

Soil.  Sand. 

Rainfall 25.72  inches  25.72  inches 

Percolation 7.58      "  21.41      " 

Evaporation 18.14      "  4-31      " 

*  Proc.  Inst.  C.-E.,  LXXIII.  p.  236. 
f  Bulletin  No.  7,  Forestry  Div.,  Dept.  Agriculture. 
Handbuch  der  Ingenieurwissenschaften;  Der  Wasserbau,  I.  Abt.,  I.  Halfte,  p.  34. 

.,   p.    38. 


EXPERIMENTS  Off  EVAPORATION  AND    PERCOLATION. 


Experiments  with  uncropped  soils  5  feet  deep  by  Gilbert  and  Laws 
at  Rothamsted,  England,  from  1870  to  1890,  gave  the  average  results 
shown  in  Table  No.  12.  The  average  percolation  through  40  inches 
of  soil  was  15.16  inches,  and  through  20  inches  was  14.38  inches. 
The  evaporation  was  much  more  uniform  than  the  percolation,  it  vary- 
ing from  11.89  to  21.74  inches,  while  the  percolation  varied  from  3.94 
to  24.38  inches.  The  soil  was  of  a  rather  heavy  character.  The  areas 
were  ToVo  acre  m  extent,  inclosed  by  cast-iron  boxes,  and  the  drainage- 
water  was  collected  and  measured.* 

TABLE    NO.  12. 

EVAPORATION    EXPERIMENTS    AT    ROTHAMSTED,    ENGLAND. 


c 

c 

o 

0 

§ 

Month. 

§1 

a  01 

a! 

S.8 

o-g 

Month. 

S| 

0/0 

11 

|l 

rt  c 

«^ 

w 

(X 

K 

W 

DM 

2e  i 

o  45 

2    06 

Tulv  .  . 

3  03 

2    26 

Oil 

2    O4 

o  60 

I    44 

August  

2  45 

I    QC 

o  50 

I    74 

0.88 

0.86 

2  86 

2    II 

o  75 

2    21 

i  .  53 

0.68 

October  

320 

I  .  70 

i  50 

May      

2    28 

i.6q 

o«  59 

3  03 

o  08 

2  05 

2.52 

1.92 

0.60 

December  

2.42 

0.61 

Average  yearly  rainfall 30.29  inches. 

"  "        evaporation 16.68       " 

"  "        percolation 13.61       " 

In  Table  No.  1 3t  are  given  the  results  of  various  European  experi- 
ments on  percolation  through  various  depths  of  soil  and  under  various 
conditions.  The  data  are  of  value  as  indicating  the  relative  percola- 
tions under  different  conditions.  The  actual  figures  must,  however,  be 
used  with  caution,  as  in  most  if  not  all  cases  the  experiments  were  so 
conducted  that  all  the  precipitation  either  percolated  or  evaporated. 
In  actual  drainage-areas  a  portion  reaches  the  stream  by  running  over 
the  surface,  most  of  the  flood-flow  being  thus  derived. 

59.  Evaporation  as  Determined  from  Stream-flow. — The  average 
evaporation  from  large  areas  as  determined  by  subtracting  stream-flow 
from  rainfall  can  be  readily  obtained  for  several  watersheds  from  the 
data  given  in  Chapter  VI.  Within  the  range  covered  by  the  data,  the 
mean  annual  evaporation  for  the  Atlantic  coast  region  obtained  in  this 
way  is  given  approximately  by  the  formula  E  =  12  +  i^»  where 
E  =  annual  evaporation,  and  R  =  annual  rainfall  in  inches.  Vermeule 
suggests  as  a  general  formula  £  =  (15.50-]-  .\6R] (.05  T  —  1.48),  in 
which  T  =  mean  annual  temperature  in  degrees  Fahrenheit.!]! 

*  Proc.  Inst.  C.  E.,  cv.  p.  31. 

f  From  Lueger.      Die  Wasserversorgung  der  Stadte,  p.  203. 

JGeolog.  Survey  N.  J.,  1894,  in.  p.  76. 


64 


EVAPORATION  AND    PERCOLATION. 


TABLE   NO.  13. 

EXPERIMENTS    ON    PERCOLATION    (LUEGER). 


Place. 

Depth  of  Soil  in 
Inches. 

Kind  of  Soil. 

With  or 
Without 
Vegeta- 
tion. 

c 
§1 

|s 

I*1"1 

Percolation  in  per  cent  of  Rainfall. 

ti 

c 

I 

C/) 

Summer. 

1 

Winter. 

i 

AbbotshilL..    . 
Holmfield  ...    . 

Lee-Bridge..    . 
« 

Rothamsted.     . 

36 
36 
36 
36 
40 

47 
49 
49 
49 
49 
49 
25 

25 

25 
50 

Sandy  loam 
Dolomitic  soil 
Sand 
Loamy  sand 
Loam  and  clay 
Clay 
Clay 
Loam 
Sandy  loam 
Clay 
Loam 
Sand 
j  Sandy  loam  ) 
}    and  clay      j 
{  Sandy  loam  ) 
")    and  clay      j 
Loam 

With 
With 
Without 
With 
Without 
With 
Without 
Without 
Without 
With 
With 
Without 

With 

Without 
Without 

26.0 

24.7 

25-7 
25-7 
31.0 
39-8 
25-7 
25-7 
25-7 
29.0 
29.0 

30.3 
24.9 

1-7 

7-7 

54-i 

22.8 

83.9 
30.3 

42.3 
19.6 

83.2 
26.5 

43-4 
28  o 

36.1 
52.4 

49-7 
59  •« 

89.7 

29-3 
45-6 
42.4 
21.3 
36.0 

26.5 
28.6 
27.9 
20.9 
32.9 

ig.O 
29.9 

37-7 
84.4 
92.0 

28.1 
41  .0 

40.5 
40.8 

58.7 
43-0 

33, 

64.2 
32-8 

« 

ii 

Tharand    ) 
Moholz  \" 
Erlangen  

30.2 

30.2 

25.8 

Oberdobling...  . 

43-3 

41.0. 

24.4 

32.0 

60.  Amount  of  Percolation  over  Large  Areas. — The  proportion  of  the 
stream-flow  that  is  derived  from  the  ground-water  or  from  the  percola- 
tion varies  greatly  for  different  watersheds.  Even  where  the  subsoil 
is  very  porous  it  is  usually  the  case  that  the  surface-soil  is  more  or  less 
clayey  and  during  heavy  rains  much  water  will  flow  off  over  the  sur- 
face. Long  Island  furnishes  an  example  of  conditions  very  favorable 
to  percolation,  the  amount  obtained  directly  from  wells  at  Brooklyn 
being  in  1894  two-thirds  of  the  total  yield  of  the  watersheds  drawn 
from.  This  is  equivalent  to  about  500,000  gallons  per  day  per  square 
mile,  equal  to  10.5  inches  or  28.5  per  cent  of  the  rainfall.  The  total 
percolation  must  have  been  at  least  12  inches,  or  three-fourths  the  total 
yield.  Experience  in  Holland  in  collecting  water  from  sand-dunes 
indicates  that  from  30  to  50  per  cent  of  the  rainfall  is  available  in  the 
ground-water.  Conditions  are,  however,  seldom  so  favorable  as  at 
these  places. 

An  approximate  estimate  of  the  total  amount  of  percolation  which 
is  useful  in  adding  to  stream-flow  or  to  ground -water  supplies  may  be 
made  for  any  particular  region  by  subtracting  the  flood-flows  of  a  stream 
from  its  total  flow,  providing  the  storage  afforded  by  small  ponds  and 
lakes  is  insignificant.  In  small  streams  the  flood-flows  increase  and 


PERCOLATION   OVER   LARGE  AREAS.  65 

decrease  so  rapidly  that  it  is  not  difficult  to  eliminate  in  this  way  most 
of  the  surface-flow. 

The  results  of  an  analysis  of  this  kind  of  the  daily  flow  of  the 
Perkiomen,  Neshaminy,  and  Tohickon,  made  from  data  given  in  the 
reports  of  the  Philadelphia  Water  Bureau,  show  that  the  annual  run-off, 
excluding  the  flood-flows,  usually  amounts  to  from  5  to  8  inches.  This 
is  equivalent  to  from  25  to  35  per  cent  of  the  total  run-off  and  12  to  18 
per  cent  of  the  rainfall. 

LITERATURE. 

1.  Greaves.      On   Evaporation    and    on    Percolation.      Proc.    Inst.    C.    E., 

1875-76,  XLV.  p.  19. 

2.  FitzGerald.     Evaporation.     Trans.    Am.   Soc.   C.   E.,    1886,   xv.   p.    581. 

Contains  results  of  experiments  at  Chestnut  Hill  Reservoir,  Boston, 
together  with  many  others  made  to  determine  the  laws  of  evapora- 
tion, and  a  full  discussion  of  the  entire  subject. 

3.  Depth  of  Evaporation  in  the   United  States..     Monthly   Weather  Review, 

September,  1888. 

4.  Harrison.     On  the  Subterranean  Water  in  the  Chalk  Formation  of  the 

Upper  Thames  and  its  Relation  to  the  Supply  of  London.  Proc. 
Inst.  C.  E.,  1890-91,  cv.  p.  2. 

5.  FitzGerald.     Rainfall,  Flow  of  Streams,  and  Storage.     Trans.  Am.   Soc. 

C.  E.,  1892,  xxvii.  p.  253. 

6.  Fernow.     Relation   of  Evaporation  to    Forests.     Bull.    No.    7,    Forestry 

Div.,  U.  S.  Dept.  Agr.     Eng.  News,  1893,  xxx.  p.  239. 

7.  Vermeule.     Report  on  Water-supply.     Geological  Survey  of  New  Jersey, 

1894,  in.  A  valuable  and  exhaustive  discussion  of  the  subject  of 
rainfall,  evaporation,  ground-storage,  and  stream-flow  as  applied  to 
New  Jersey. 

8.  Handbuch  der  Ingenieurwissenschaften,  Band  in,  Abt.  i,  i.  Halfte,   and 

Lueger,  Wasserversorgung  der  Stadte,  contain  many  references  to 
the  foreign  literature  of  this  subject. 

9.  Kimball.     Evaporation  Observations  in  the  United  States.     Eng.  News, 

1905,  LIU.  p.  353. 


CHAPTER  VI. 
FLOW  OF  STREAMS. 

61.  General  Methods  of  Procedure. — When  a  stream  is  under  con- 
sideration as  a  source  of  water-supply,  the  peculiarities  of  its  flow — the 
minimum,  maximum,  and  total  flow'  for  various  periods  of  time — are 
among  the  first  things  to  be  determined.     The  most  accurate  as  well 
as  the  most  direct  method  of  determining  these  is  by  means  of  a  series 
of  gaugings  extending  over  several  years,  which,  to  be  of  the  greatest 
value,  should  include  periods  of  high  flood  and  periods  of  drought.     A 
long  series  of  gaugings  is,  however,  seldom  available  at  the  time  when 
a  source  must  be   decided   upon,    but  by  establishing   gauges  at  the 
earliest  possible  moment  much  valuable  information  may  be  had  by  the 
time  detailed  designs  are  required.      This  applies  especially  to  the  case 
of  a  city  seeking  an  additional  supply. 

Where  gaugings  are  not  to  be  had,  or  where  they  are  very  limited 
in  extent,  as  close  an  estimate  as  possible  must  be  made  from  a  com- 
parison with  other  streams  whose  flows  are  known,  taking  into  account 
as  far  as  may  be  the  differences  in  rainfall,  climate,  and  in  the  various 
characteristics  of  the  different  watersheds.  Where  such  differences  are 
great  this  method  will  give  results  only  roughly  approximate,  but  still 
much  better  than  mere  guesses  and  quite  sufficient  in  many  cases  to 
determine  the  availability  of  a  given  source.  Where,  however,  the 
margin  is  close,  and  in  problems  pertaining  to  the  detailed  design,  a 
more  accurate  knowledge  is  greatly  to  be  desired.  It  can  be  obtained 
only  by  means  of  gaugings. 

62.  Influences    Affecting    Stream-flow. — All    streams    derive    their 
supply  ultimately  from  the  rainfall,  and,  in  general,  the  amount  of  the 
run-ofTis  equal  to  the  rainfall  less  the  evaporation.      In  the  last  chapter 
the  various  influences  affecting  evaporation  and  percolation  were  dis- 
cussed,  and  it  only  remains  to  consider  how  the  variations  in  these 
factors  go  to  affect  stream-flow. 

Whatever  augments  evaporation  decreases  stream-flow,  and  by  the 

66 


UNITS   OF  MEASURE.  67 

same  amount.  Thus  a  watershed  with  a  large  percentage  in  grass  will 
yield  a  less  amount  than  one  with  rocky  and  barren  hillsides;  one  with 
a  large  percentage  of  water-surface,  less  than  one  with  a  small  per- 
centage. Again,  the  higher  the  temperature  the  greater  the  evaporation 
and  the  less  the  stream-flow.  An  increased  rainfall  will  also  increase 
the  evaporation,  but  the  relative  increase  in  evaporation  will  be  less  than 
that  in  the  rainfall ;  hence  the  larger  the  rainfall  the  greater  the  per- 
centage flowing  off.  The  distribution  of  the  rainfall  throughout  the 
year  also  affects  greatly  the  evaporation  and  consequently  the  stream- 
flow. 

The  effect  of  large  percolation  is  to  make  the  run-off  more  uniform ; 
but  where  the  water  is  held  for  the  use  of  vegetation  by  a  porous  soil, 
a  large  percolation  may  result  in  a  decreased  total  flow.  Steep,  rocky 
hillsides  will  give  a  large  per  cent  of  the  rainfall  to  the  streams,  but  the 
flow  will  be  very  irregular;  flat  grass-lands  will  give  little  or  nothing 
to  the  streams  during  the  season  of  growth.  Again,  the  winter  climate 
has,  through  its  effect  on  percolation,  an  important  influence  on  the 
regularity  of  the  flow.  When  the  ground  is  frozen,  little  water  goes 
to  replenish  the  ground-storage  during  the  melting  of  the  snow,  but  if 
the  soil  is  open  to  winter  rains  and  snows,  much  water  will  be  furnished 
through  percolation  to  increase  the  summer  flow,  while  the  spring  floods 
will  be  correspondingly  reduced.  This  effect  of  climate  is  well  illus- 
trated in  Fig.  15,  page  82,  in  the  curves  for  the  Connecticut  and 
Savannah  rivers. 

It  is  thus  seen  that  temperature,  topography,  vegetation,  and  soil, 
as  well  as  the  amount  of  rainfall,  are  important  factors  to  be  considered 
in  a  study  of  the  flow  of  a  stream. 

It  should  here  be  noted  that  from  any  given  area  of  watershed  a 
portion  of  the  percolating  water  is  likely  to  escape  to  a  lower  point  of 
the  valley  before  coming  to  the  surface.  The  amount  lost  in  this  way, 
although  usually  insignificant,  is  sometimes  very  large.  This  question, 
together  with  methods  of  utilizing  such  water,  is  discussed  in  subsequent 
chapters ;  for  the  present  it  will  be  assumed  that  this  portion  is  so  small 
in  amount  that  it  may  be  neglected. 

63.  Units  of  Measure. — Rainfall  is  expressed  in  inches  in  depth,  and 
the  rate  in  inches  per  hour  or  per  twenty-four  hours ;  and  for  compara- 
tive purposes  stream-flow  is  often  likewise  expressed,  meaning  thereby 
inches  in  depth  over  the  entire  watershed.  For  other  purposes  the 
flow  is  usually  expressed  in  cubic  feet,  or  cubic  feet  per  square  mile  of 
watershed,  and  the  rate  of  flow  in  cubic  feet  per  second,  or  cubic  feet 
per  second  per  square  mile.  The  foot  and  second  units  are  also  con- 


68 


FLOW  OF  STREAMS. 


venient  to  use  in  all  hydraulic  formulas,  but  in  matters  pertaining  to 
storage  and  distribution  the  gallon  unit  is  in  common  use,  and  rates 
are  expressed  in  gallons  per  minute  and  gallons  per  twenty-four  hours. 
For  convenience  in  computations  relative  to  rainfall  and  flow  of 
streams,  the  following  table  is  inserted. 

TABLE   NO.  14. 

VOLUMES     AND     RATES     OF    FLOW    IN     FEET    AND     SECONDS     CORRESPONDING    TO     GIVEN 
VOLUMES    AND    RATES    OF    RAINFALL    IN    INCHES    AND    HOURS. 


Depth  in 
Inches. 

Cubic  Feet  per 
Square  Mile. 

Inches  per 
Hour. 

Cubic  Feet  per 
Second  per  Square 
Mile. 

Inches  per 
24  Hours. 

Cubic  Feet  per 
Second  per  Square 
Mile. 

O.  I 

232,320 

O   I 

64.5 

I 

26.9 

O.2 

464,640 

O.  2 

129.0 

2 

53-8 

0-3 

696,960 

0-3 

193-5 

3 

80.7 

0.4 

929,280 

0.4 

258.1 

4 

107-5 

-       0.5 

I,i6it6oo 

0-5 

322.6 

5 

134-4 

0.6 

1,393,920 

0.6 

3S7.I 

6 

161.3 

0.7 

1,626,240 

0.7 

451-7 

7 

188.2 

0.8 

1,858,560 

0.8 

516.2 

8 

215.1 

0.9 

2,090,880 

0-9 

580.7 

9 

242.0 

I.O 

2,323,200 

I.O 

645-3 

10 

268.9 

One  inch  of  rain  =  2,323,200  cu.  ft.  "per  sq.  mile. 

One  inch  per  hour  =  645.33  cu.  ft.  per  sec.  per  sq.  mile. 
One  inch  per  24  hours  =  26.89  cu.  ft.  per  sec.  per  sq.  mile. 
One  cubic  foot  =  7.4805  U.  S.  gallons. 

One  cubic  foot  per  sec.  =  646,300  gallons  per  day. 

64.  Divisions  of  the  Subject- — The  question  of  the  flow  of  streams 
naturally  divides  itself  into  three  parts : 

First,  the  minimum  flow  of  the  stream. 

Second,  the  maximum  or  flood  flow. 

Third,  variations  in  the  flow  through  successive  months  and  years. 

The  first  information  is  necessary  in  case  a  stream  is  under  consid-» 
eration  for  which  but  little  storage  is  obtainable,  or  in  answer  to  the 
question  whether  it  is  practicable  to  draw  directly  from  the  stream 
without  storage.  The  second  is  of  great  importance  in  the  design  and 
execution  of  all  river  work,  and  especially  in  determining  the  size  of 
waste- weirs.  The  third  determines  the  supplying  capacity  of  the  water- 
shed and  the  size  of  impounding  reservoirs. 

MINIMUM    FLOW. 

65.  The  dry-weather  flow  of  streams  is  maintained  entirely  from 
ground-  and  surface-storage ;  and  as  facilities  for  such  storage  vary  in 


MAXIMUM  FLOW.  69 

different  watersheds,  so  will  the  minimum  flow  vary.  Surface-storage, 
if  consisting  of  large  areas  of  shallow  lakes  and  ponds,  acts  to  decrease 
greatly  the  total  flow  of  a  stream  on  account  of  the  great  evaporation, 
while  at  the  same  time  it  usually  increases  the  minimum  flow. 

In  Table  No.  I  5  on  page  70  are  given  the  minimum  flows  of  several 
streams  in  different  localities.  For  streams  in  the  northern  Atlantic- 
coast  States  these  and  other  statistics  indicate  that  for  watersheds  of  less 
than  200  square  miles  in  area  the  minimum  flow  varies  from  nearly 
zero*  to  about  o.  2  cubic  foot  per  second  per  square  mile,  averaging  o.  10 
or  Q.  12.  For  large  streams  the  minimum  is  rarely  less  than  o.  10,  and 
in  some  cases  is  as  high  as  0.30,  the  latter  figure  being  about  the  mini- 
mum flow  for  the  Connecticut  with  an  area  of  10,234  square  miles,  and 
for  the  Merrimack  with  4599  square  miles  of  watershed.  In  the  upper 
Mississippi  valley  the  minimum  flow  is  much  less,  as  indicated  by  the 
data  for  the  Rock,  the  Illinois,  and  the  Des  Plaines  rivers.  Streams 
in  this  locality  of  several  hundred  square  miles  of  watershed  are  likely 
to  have  a  minimum  of  zero,  while  still  further  west  this  applies  to 
streams  of  thousands  of  square  miles  of  catchment-area. 

MAXIMUM    OR    FLOOD    FLOW. 

66.  General  Considerations. — The  maximum  rate  at  which  the  waters 
from  great  storms  will  pass  down  a  stream  is  affected  largely  by  the 
steepness  of  the  slopes,  by  the  size  and  shape  of  the  drainage-area,  and 
by  the  distribution  of  the  branches.  Small  areas  will  have  larger 
maximum  rates  of  flow  than  large  areas,  other  things  being  equal,  as 
the  former  are  affected  by  short  rainfalls  of  high  rates,  while  in  the 
latter  case  the  maximum  flows  are  caused  by  rains  of  longer  duration 
but  of  less  intensity.  For  a  like  reason  streams  with  steep  slopes  will 
have  a  higher  maximum  rate  than  those  with  flat  slopes. 

The  evaporation  which  takes  place  during  a  flood  is  of  so  little 
importance  that  its  effect  may  be  neglected.  Percolation  absorbs  large 
portions  of  heavy  rains  if  the  ground  is  dry,  but  such  rains  are  quite  as 
apt  to  occur  with  the  ground  already  soaked  or  even  frozen,  so  that  in 
the  extreme  case,  which  is  the  one  that  must  be  considered,  percolation 
is  of  small  moment. 

Of  much  greater  importance  in  distributing  the  run-off  over  a  long 
interval  of  time,  and  so  reducing  the  maximum  rate,  is  the  surface 
storage  of  natural  lakes  and  ponds  and  of  those  created  by  the  inunda- 
tion of  large  flats  bordering  the  stream.  The  effect  of  this  last  factor 
may  be  sufficient  to  reduce  the  flood-flow  to  one-half  or  one-fourth  that 
of  a  stream  with  a  narrow  valley. 


FLO  W  OF  STREAMS. 


67.  Data  of  Maximum  Rates  of  Flow.  —  In  Table  No.  1 5  are  given 
data  concerning  the  maximum  flow  of  I  streams  taken  mainly  from 
Water-supply  Paper  No.  147,  U.  S.  G.  S.,  by  E.  C.  Murphy.  Much 
detailed  information  concerning  floods  is  given  in  this  paper  and  in 
other  Water-supply  Papers  of  the  Survey.  A  great  variation  is 
observable  in  the  table,  due  partly  to  the  varying  rates  of  rainfall,  but 
largely  to  the  differing  characteristics  of  the  streams.  Nevertheless  the 
data  will  be  of  some  assistance  in  estimating  probable  maximum  floods. 

TABLE    NO.    15. 

MINIMUM   AND    MAXIMUM   FLOW   OF    STREAMS. 


Stream. 

Place. 

Drainage  area; 
square  miles. 

3* 

ifS 

*i 

en 
l»      • 

6  ft~ 

;a  d  'a 

Sjj 

3* 

*8. 

In 

E: 

3    £      • 
g    ftjg 

'*    +i  "& 
rt  ^    *" 
| 

* 
£ 

"3 
< 

Skinner  Creek  
Coldspring  Brook    
Croton  River,  S.  Branch    .    . 
\Voodhull  Reservoir 

Northeastern  United  States: 
Mannsville,  N.  Y  
Massachusetts    
New  York  
Herkimer,  N.  Y  

6.40 

6-43 

7.80 
0.40 

... 

124.20 
48.40 

73-90 

77.80 

(23) 

i 
( 

Stony  Brook.    .                    . 

Boston,  Mass  

12  .  7 

I  2  I  .  OO 

t 

Great  River  

Westfield,  Mass  

14.0 

71  .40 

t 

Swartswood  Lake    

New  Jersey     

16.0 

68.00 

t 

Williamstown  River    .... 
Croton  River,  W.  Branch 

Williamstown,  Mass.     .    .    . 
New  York  

16.5 

20.  S 

O.O2O 

34.00 
54.40 

< 
i 

Beaverdam  Creek    

Altmar,  N.  Y  

20.  7 

I  I  I  .  00 

i 

Trout  Brook     
Wautuppa  Lake  

Centerville,  N.  Y  
Fall  River,  Mass  

23.0 
28.5 

50.60 
72.00 

1 

Pequest  River       
Sawkill 

Huntsville,  N.  J  

New  Jersey 

31-4 

•If    O 

19.30 

228.60 

, 

Whippany  River  . 

Whippany,  N.  J  

37.0 

61.62 

< 

Cuyadutta  Creek 

Johnstown   N.  Y. 

40  o 

72  .40 

< 

West  Canada  Creek 

Motts  Dam,  N.  Y.        ... 

47   "> 

34-  10 

< 

Pequannock  River 

New  Jersey 

48.0 

i  i  5  .  oo 

(12) 

South  Fork  

Croyole  Tp.,  Pa  

48.6 

2  i  5  .  oo 

(6) 

Sauquoit  Creek        

New  York  Mills,  N.  Y.    .    . 

fl  .  C 

^3.40 

(23) 

Rockaway  River  

Dover,  N.  J  

<2  .  2 

47.00 

« 

Oneida  Creek       

Kenwood,  N.  Y  

SQ.O 

41.20 

« 

Flat  River     

Rhode  Island     

61  .0 

120.75 

(2) 

Camden  Creek     
Nine  Mile  Creek      
Wissahickon  Creek      .... 

Camden,  N.  Y  
Stittville,  N.  Y  
Philadelphia,  Pa  

61.4 
62.6 
64.6 

0.232 

24.10 
124.90 
43.50 

(23) 
<« 

Sandy  Creek 

Allendale  N  Y 

68  4 

87.70 

« 

Rock  Creek 

Washington    D   C 

77    <s 

126.  30 

(3) 

Sudbury  River 

Framingham    !Mass 

1  /  •  3 

78  o 

O.O36 

44-  2 

(s) 

Hockanum  River  
Nashua  River  

Connecticut    
Massachusetts 

79.0 

84  i; 

78.10 
71  .04 

(23) 

Independence  Creek        .    .    . 
Deer  River   

Crandall,  N.  Y  
Deer  River,  N.  Y.         ... 

93-2 

IOI 

66.50 
78.10 

«« 
«« 

Wanaque  River   

New  Jersey     

IOI 

66.00 

« 

Tohickon  Creek  

Point  Pleasant,  Pa  

IO2 

O.OO2 

112.50 

« 

Fish  Creek,  E.  Branch  .    .    . 
Nashua  River  

Point  Rocks,  N.  Y  
Massachusetts    

104 
ICQ 

80.50 
104-53 

H 

(2) 

*  See  references  at  end  of  chapter. 


FLOW  OF  STREAMS. 


TABLE  NO.    15.  —  Continued. 

MINIMUM   AND  MAXIMUM   FLOW   OF   STREAMS. 


Stream. 

Place. 

Drainage  area; 
square  miles. 

3  t 

j?K 
ll 

I*.- 

C              T^n 

'3  d  6 
2 

d  cr 

8    w 

i* 

j 

3    <u 

6  a^ 

s«  e 

Authority.* 

Sandy  Creek,  N.  Branch   .    . 
Scan  tic  River  N   Branch 

Adams,  N.  Y  
Connecticut            .    . 

110 

118 

%'£ 

(23) 

«« 

Mahwah   N  J 

118 

0A  •  0(J 

a 

Boonton   N  J. 

1  u;>  •  uy 

CTT^ 

Paulirskill  River 

New  Jersey                    .    . 

j.iy 
126 

ft 

(TT^ 

Patuxent  River 

Laurel   M!d 

I  37 

\j.  13 

JT" 

31    2O 

(2?\ 

Pennsylvania 

I  3Q 

o  ooo 

O7    60 

\*SJ 

(18} 

Oriskany  Creek   

Colemans,  N.  Y  

141 

ttf    80 

(23) 

Perkiomen  Creek     

Frederick,  Pa.        

I<2 

o  30 

IO<   4 

(18) 

Mohawk  River     

Ridge  Mills,  N.  Y  

IC-J 

5 
46  40 

(23) 

Ramapo  River     
Fish  Creek,  W.  Branch      .    . 
Pawtuxet 

Pompton,  N.  J  

McConnellsville,  N.  Y.     .    . 
Rhode  Island     

160 
187 

IQO 

o.  140 

66.10 
32.70 
?6  o 

<« 
« 

(2} 

Salmon  River 

Altona,  N.  Y  

221 

27  60 

(2^ 

Black  River 

Forestport,  N.  Y  

268 

3O    OO 

\*6) 
« 

South  Branch 

New  Jersey     

276 

IOO 

Cl2>i 

Croton  River 

Croton  Dam,  N.  Y  

33Q 

O    I  CO 

74    OO 

(l1\('2\ 

Great  River 

Westfield,  Mass  

3<O 

T  f  T        AQ 

(2^ 

East  Canada  Creek 

Dolgeville,  N.  Y  

3<;6 

24    7O 

W) 

Moose  River    
Stony  Creek                              . 

Agers  Mill,  N.  Y  
Johnstown,  Pa  

407 
428 

31.00 

70  oo 

tl 
H 

West  Canada  Creek    .... 
Farmington  River 

Middleville,  N.  Y  
Connecticut     

5i8 

rg4 

24.90 

41    7O 

(« 
tt 

Monocacy  River      .        ... 

Frederick,  Md  

665 

o  116 

29    80 

U 

Passaic  River   .        

Little  Falls,  N.  J  

773 

o  100 

24    2O 

(t 

North  River          

Port  Republic,  Va  

/  /o 
804 

o  220 

29    80 

ft 

Dundee   N  J 

823 

43     38 

tt 

North  River      

Glasgow,  Va  

023 
831 

o  180 

43-  6° 
44    80 

tt 

Raritan  River  

Boundbrook,  N.  J  

"o* 

870 

O    I4O 

tj  Q      7O 

tt 

Potomac,  N.  Branch  .... 
Black  River 

Cumberland,  Md  
Lyons  Falls  N  Y 

891 
80  7 

O.O22 

22.80 

tt 
tt 

Schoharie  Creek 

Fort  Hunter  N  Y 

O48 

tt 

Genesee  River      

Mount  Morris,  N.  Y.    .    .    . 

1,070 

OOQ4 

3Q    2O 

ft 

M^ohawk  River 

Little  Falls  N  Y 

i  306 

21    83 

(23^ 

Greenbrier  River 

Alderson  W^  Va.           . 

I   344 

l«r 

Black  River     . 

Carthage,  N.  Y  

I  8l2 

(< 

Chemung  River   

Elmira,  N.  Y  

2,O?  C 

67  10 

(TA\ 

Androscoggin  River     .... 

Rumford,  Me  

2  22O 

2  1    OO 

(2T.\ 

Mohawk  River    

Rexford,  N.  Y  

3  384 

23    IO 

^3' 

Kennebec  River 

Waterville  Me 

2C    2O 

n 

Hudson  River      

Mechanicsville,  N.  Y.   .    .    . 

4,  COO 

*5  •  ^u 

1$    CO 

a 

M^errimac  River 

Lawrence,  ^lass. 

4r  e  •} 

O    31 

23    4O 

a 

Potomac  River     
Delaware  River   
Susquehanna  River     .... 
Connecticut  River   .        ... 

Dam,  No.  5,  Md  
Lambertville,  N.  J  

Northumberland,  Pa.   ,.    .    .. 
Holvoke   M^ass 

4,640 
6,500 
6,800 

8  660 

0.78 

43.  qv 
22.2O 
53-80 

I7-SO 
21    IO 

t 
t 

Connecticut  River   

10,234 

O    <I 

2O    3O 

i 

Potomac  River     

Maryland    

11,043 

42    60 

i 

Potomac  River    

Great  Falls,  Md.            .    . 

1  1  ,427 

41    2O 

t 

Susquehanna  River     .... 

Harrisburg,  Pa  

24,030 

18.90 

< 

*  See  references  at  end  of  chapter. 


FLOW  OF  STREAMS. 


TABLE  NO.   15.—  Continued. 

MINIMUM   AND   MAXIMUM   FLOW   OF   STREAMS. 


d   cr 

s   d* 

O     tfl 

oJ  _a> 

1  & 

i'5 

*. 

Stream. 

Place. 

ci'g 

0?     0) 

s! 

1 

I 

|  &g 

6  ft^ 

3 

•g  £ 

!s  £  s 

ctf  "«    ^ 

Q 

a 

s 

Southeastern  United  States: 

Carters,  Ga  

0.588 

31.86 

M 

Etowah  River 

Canton   Ga 

o  405 

31  50 

u 

Tuckasegee  River    

Bryson,  N.  C  

662 

^8.23 

u 

Little  Tennessee  River  .    .    . 

Judson,  N.  C  

67? 

0.408 

I 

Broad  River  

Carlton  Ga  

762 

o.  344 

38.22 

I 

Catawba  River            . 

Catawba  N  C 

i  535 

O    CC3 

r  -i    jo 

( 

Yadkin  River  .            ... 

Salisbury  N  C 

33QQ 

31    60 

I 

Tallapoosa  River 

Milstead   Ala 

3  840 

18  23 

I 

Broad  River     .    .             . 

Alston   S  C 

4600 

28   44 

f 

Black  Warrior  River  .... 

Tuscaloosa,  Ala  

4,000 

27.80 

( 

Savanna  River     

Augusta  Ga 

72Q4 

42    ^O 

l 

Tennessee  River  

Chattanooga  Tenn        . 

21  418 

2O    80 

t 

Central  United  States: 

Des  Plaines  River 

Riverside   111 

6  o 

o  o 

21    4 

,              V 

Rock  River  

Rockford,    111  

6,500 

0.016 

(136) 

Mississippi  River     

St.  Paul,  Minn  

6,0853 

19.70 

(23) 

68.  Formulas  for  Flood-flows.  —  Various  formulas  have  been  pro- 
posed for  expressing  the  maximum  flow  of  a  stream,  some  involving 
only  the  rainfall  and  area,  while  others  attempt  to  take  account  also  of 
the  slope  and  shape  of  the  watershed.  Obviously  any  formula  which 
does  not  involve  the  last  two  factors  is  not  of  general  application, 
although  it  may  give  good  results  for  a  particular  class  of  streams.  In 
applying  such  a  formula  to  other  streams  due  allowance  must  be  made 
for  the  differing  conditions. 

Among  the  most  widely  known  of  this  class  of  formulas  is  that 
given  by  Fanning  and  recommended  by  him  as  applicable  to  average 
New  England  and  Middle-State  basins.  It  is 


in  which  Q  =  discharge  in  cubic  feet  per  second  per  square  mile,  and 
M  =  area  in  square  miles.  Thus  the  total  discharge  is  made  to  vary 
according  to  M*.  The  discharges  given  by  this  formula  have  been 
materially  exceeded  in  some  cases,  especially  for  the  smaller  water- 
sheds, and  have  been  reached  by  floods  caused  by  rains  much  below 

*  See  references  at  end  of  chapter. 


FLO  IV  OF  STKEAMS. 


73 


the  maximum.     It  gives  a  value  of  Q  which  appears  to  increase  some- 
what too  slowly  with  decrease  in  area. 

Another  formula  derived  from  measurements  of  streams  of  flat 
slopes  in  the  upper  Mississippi  valley  is  that  proposed  by  Cooley  *  and 
is 


Q  =  180 


M 


It  is  intended  to  represent  those  floods  occurring  with  comparative  fre- 
quency, as  once  in  six  or  ten  years.  Several  other  formulas  are  given 
by  Mr.  Cooley  in  the  paper  referred  to. 

It   may  be  here   noted   that  the  waste-weirs  of   the  dams  of   the 
Boston  Water-works  are  designed  to  carry  a  flood-volume  at  the  rate 


CCSO       tSCO       2750       8000      3ZSO      3500       3760      4OOO      4UB      AfaO      47*0       SOOO 


AREA  Or  DRAINAGE    BASIN- SQ  MILES 

FIG.  i2a.  —  RELATION  BETWEEN  FLOOD  DISCHARGE  AND  DRAINAGE  AREA  (KTJICHLING). 
of  6  inches  per  24  hours,  or  161  cubic  feet  per  second  per  square  mile. 
The  watersheds  are  from  20  to  75  square  miles  in  area. 

The  relation  between  flood-flow  and  drainage  area  is  well  shown 
in  Fig.  I2a,  from  Kuichling's  report  on  the  Water-supply  for 
the  New  York  Barge  Canal. f  On  this  diagram  are  plotted  the 

*    Jour,  West.  Soc.  Engrs.,  1896,  I.  p.  306. 

f  Report  of  State  Engineer  on  Barge  Canal,  1901,  p.  844.  This  paper  contains  a  dis- 
cussion of  many  formulas. 


74  FLOW  OF  STREAMS. 

data  of  Table  No.  15  and  numerous  other  data  relating  to  Ameri- 
can and  European  rivers.  Curve  No.  i  represents  floods  which 
may  occur  occasionally  and  curve  No.  2  those  which  may  occur  but 
rarely. 

Mr.  Murphy,  in  Water-supply  Paper  No.  147  already  quoted,  plots 
in  a  similar  manner  data  for  streams  in  the  northeastern  United  States 
obtaining  a  curve  whose  equation  is 


This  gives  somewhat  lower  values  than  Mr.  Kuichling's  "  Curve 
No.  i." 

69.  Rational  Method  of  Estimating  Flood-flow.  —  A  more  rational 
method  than  by  the  use  of  a  formula,  and  one  which  is  applicable  to 
any  area,  has  been  proposed  by  some  engineers,  most  recently  by 
Mr.  Chamier  in  a  paper  before  the  Institution  of  Civil  Engineers.  *  It 
is  based  upon  the  following  principles  : 

Assuming  a  uniform  rate  of  rainfall,  the  flow  of  a  stream  will 
increase  rapidly  until  a  sufficient  time  has  elapsed  for  water  to  reach 
the  point  in  question  from  all  parts  of  the  drainage-area.  After  this, 
with  a  continuation  of  the  rain,  the  increase  in  flow  will  be  much 
slower,  being  now  due  to  the  increase  in  the  percentage  flowing  off. 
The  maximum  flood  will  then  probably  be  produced  by  the  greatest 
possible  rainfall  of  a  duration  corresponding  to  the  length  of  time  above 
mentioned.  Rates  of  rainfall  of  long  duration  are  far  from  uniform,  but 
irregularity  in  the  rate  within  the  time  required  for  the  concentration 
of  the  water  to  the  point  of  discharge  will  have  little  effect  on  the 
maximum  rate  of  flow. 

The  elements  to  be  determined  in  this  method  are  then  :  (i)  the 
length  of  time  required  for  the  water  from  the  most  remote  part  of  the 
watershed  to  reach  the  point  of  discharge  ;  (2)  the  maximum  rate  of 
rainfall  of  a  duration  equal  to  this  time  ;  and  (3)  the  percentage  flowing 
off.  The  maximum  rate  of  flow  will  then  be  equal  to  this  rate  of  rain- 
fall multiplied  by  the  percentage  as  above  found. 

(i)  The  Time  Required.  —  In  estimating  this  time  the  maximum 
distance  to  be  covered  can  be  obtained  from  a  good  map  of  the  area 
in  question,  making  due  allowance  for  the  sinuosities  of  the  smaller 
channels.  The  velocities  of  flow  are  more  difficult  of  estimation.  In 

*  Proc.  Inst.  C.  E.,  1898,  cxxxiv.  p.  313.  Abstracted  in  Engineering  Record,  1899, 
xxxix.  p.  163. 


MAXIMUM  FLOW.  75 

channels  of  considerable  size  they  may  be  roughly  estimated  by 
Kutter's  formula,  the  slopes  and  high-water  cross-sections  being 
known.  For  smaller  branches  the  velocity  will  usually  range  from 
two  to  four  miles  per  hour,  though  in  some  cases  it  may  be  consider- 
ably higher.  On  lateral  slopes,  before  reaching  well-defined  channels, 
the  water  will  move  at  a  slow  velocity,  estimated  by  Mr.  Chamier  at 
from  one-half  to  one  mile  per  hour.  In  any  case  an  approximate 
estimate  of  velocity  in  the  various  channels  can  be  made  by  a  few  direct 
observations  during  moderately  high  water. 

A  good  notion  of  the  total  time  required  for  the  concentration  of 
the  water  may  also  be  obtained  by  observing  the  time  which  elapses 
from  the  beginning  of  a  sudden  storm  until  the  maximum  effect  is  felt 
at  the  point  of  discharge.  Where  the  country  is  level  and  the  drainage- 
channels  far  apart,  or  where  there  is  large  surface  storage,  this  would 
be  the  most  reliable  method  of  estimating  the  time. 

If  the  element  of  time  is  correctly  determined,  the  effects  of  size 
and  shape  of  area,  of  slopes,  and  of  surface  storage  will  all  have  been 
taken  account  of  to  a  very  large  degree. 

(2)  The  Rate  of  Rainfall. — The  time  having  been  determined,  the 
corresponding  rainfall  may  be  taken  from  the  data  of  the  last  chapter. 
To  the  estimated  rainfall,  if  occurring  in  the  winter,  may  be  added  a 
maximum  of  about  2  inches  for  melting  snow. 

(3)  The  Percentage  Flowing  Off. — The  total  flood-discharge  of  a 
stream  at  times  when  the  ground  is  previously  soaked  or  frozen  will 
usually  vary  from  '50  to  75  per  cent  of  the  rainfall.      The  percentage 
running  off  during  the  rise  of  a  stream  will,  however,  be  considerably 
less  than  the  total  percentage  for  the  entire  flood,  on  account  of  the 
effect  of  pondage  and  the  greater  percolation  during  the  first  part  of  the 
storm.      In  the  paper  already  referred  to  Mr.  Chamier  estimates  the 
percentages  for  different  conditions  as  follows: 

For  flat  country,  sandy  soil,  or  cultivated  land,  25  to  35  per  cent. 

For  meadows  and  gentle  declivities,  absorbent  ground,  35  to  45 
per  cent. 

For  wooded  hill-slopes  and  compact  or  stony  ground,  45  to  55  per 
cent. 

For  mountainous  and  rocky  country  or  non-absorbent  surfaces,  as 
frozen  ground,  55  to  65  per  cent. 

70.  Diagram  for  Flood-flows. — The  diagram  Fig.  13  gives  directly 
the  rate  of  flood-flow  corresponding  to  various  percentages  and  various 
values  of  the  time  required  for  the  concentration  of  the  flood-waters  as 
determined  under  (i).  It  is  constructed  on  the  basis  of  rainfalls 


FLOW  OF  STREAMS. 


according  to  the  middle  curve  of  Fig.  12,  page  51,  or  the  lower  curve 
with  2  inches  added  for  snow.  For  small  areas  in  which  the  maximum 
flow  is  normally  reached  in  three  or  four  hours,  an  allowance  of  I  inch 
for  snow  would  be  sufficient. 

In  making  use  of  this  diagram  it  should  be  remembered  that  it  is 
based  on  very  excessive  and  rare  rainfalls,  and  therefore  the  flood-flows 


\20C 


0     -+      Q      /a     /6     eo     8*    ze    32    36     **o   <++    +Q 

T/me  i/7  hours  re<jru/r*af  for  Co/jcenfrcrf/oti  of  Hood  Waters. 

FIG.  13. — FLOOD-VOLUMES. 

resulting  will  be  the  extraordinary  floods  which  may  occur  perhaps  once 
or  twice  in  a  century.  Such,  however,  must  be  provided  for  in  design- 
ing waste-weirs  where  inadequate  dimensions  would  endanger  the  lives 
of  the  population  in  the  valley  below.  For  structures  where  a  failure 
would  mean  a  property  loss  only,  it  would  often  be  more  economical 
to  provide  for  ordinary  floods  only,  in  which  case  a  less  rate  of  rainfall 
should  be  adopted  according  to  local  conditions. 

71.  Example. — To  illustrate  the  use  of  the  foregoing  method,  let  it  be 
required  to  estimate  the  flood-flow  of  a  certain  stream  of  a  drainage-area  of 
50  square  miles,  with  steep  side  slopes  and  a  long  valley.  The  length  of  the 
valley  is,  say,  15  miles,  and  actual  length  of  the  main  channel  25  miles,  with 
5  miles  of  smaller  channels  reaching  to  the  farthest  part  of  the  area.  The 
time  required  for  the  water  to  get  to  the  small  channels  may  be  one  hour,  to 
flow  the  5  miles  two  hours,  and  the  25  miles  eight  hours,  or  a  total  of 
eleven  hours.  The  summer  rainfall  to  be  expected  in  this  time  is,  from  Fig. 
12,  p.  51,  about  6  inches,  or  at  the  rate  of  about  13  inches  in  24  hours.  The 
percentage  may  be  taken  at  50,  giving  therefore  a  rate  of  flow  of  6^  inches  per 
24  hours,  or  174  cubic  feet  per  second  per  square  mile.  Or,  using  the  diagram 
of  Fig.  13,  we  find  that  for  a  time  value  of  n  hours  and  a  percentage  of  50 
the  flood-flow  is  about  180  cubic  feet  per  second  per  square  mile. 

For  a  stream  of  the  same  area  but  having  a  watershed  nearly  circular,  the 
distance  would  be  reduced  to  perhaps  one-half  the  above,  and  the  time  to  six 
hours,  corresponding  to  a  rainfall  of  5  inches  or  a  rate  of  £  inch  per  hour, 


MAXIMUM  fLOW.  77 

which,  with  a  percentage  of  50,  would  give  the  high  rate  of  270  cubic  feet 
per  second  per  square  mile. 

72.  Some  Great  Floods. — On  March  30  and  31,  1889,  there  occurred  a 
great  storm  over  a  large  part  of  Pennsylvania  and  New  York  which  caused 
very  high  floods  in  many  streams.  The  great  Johnstown  disaster  was  one  of 
the  results  of  this  storm.  It  was  caused  by  floods  in  the  South  Fork  of  the 
Connemaugh  River,  a  stream  with  a  drainage-area  of  48.6  square  miles  and  a 
length  of  10  miles.  An  estimate  made  by  an  investigating  committee  of  the 
American  Society  of  Civil  Engineers*  placed  the  maximum  rate  of  flow  at 
about  215  cubic  feet  per  second  per  square  mile.  The  rainfall  amounted  to 
from  6  to  8  inches  on  May  30  and  31,  it  being  estimated  that  for  several 
hours  rain  fell  at  the  rate  of  f  inch  per  hour.  The  estimated  rate  of  flow 
would  be  equal  to  one-half  of  this. 

This  same  storm  caused  a  flood  in  the  Chemung  River  at  Elmira,  N.  Y., 
a  stream  with  a  watershed  of  2055  square  miles,  which  was  estimated  by 
Mr.  Collingwood  at  138,000  cubic  feet  per  second  or  67.1  cubic  feet  per 
second  per  square  mile.f  The  rainfall  varied  from  6  to  nearly  10  inches, 
averaging  about  7,  the  larger  portion  falling  in  12  hours  or  less.  The  extreme 
length  of  the  watershed  is  about  50  miles;  the  slopes  are  moderate,  and  it 
would  probably  require  at  least  24  hours  for  the  maximum  flood-point  to  be 
reached.  On  this  basis  the  maximum  flow  of  67.  i  cubic  feet  per  second  per 
square  mile,  or  2.5  inches  per  24  hours,  would  be  35  per  cent  of  the  average 
rate  of  rainfall  for  this  length  of  time. 

On  Feb.  6,  1896,  great  floods  were  caused  in  New  Jersey  by  a  rain  of 
about  3.7  inches  (most  of  which  fell  in  24  hours)  and  the  simultaneous  melt- 
ing of  snow  estimated  equal  in  amount  to  about  o.  6  inch  of  rain,  making  a 
total  of  4. 3  inches.  Of  this,  from  2. 5  to  3  inches  was  discharged  as  flood-flow, 
the  remainder  being  absorbed  by  the  ground.];  The  total  run-off  was  therefore 
about  two-thirds  or  66  per  cent.  The  percentage  for  the  first  half  of  the  flow 
would  be  perhaps  50.  The  effect  of  the  snow  was  at  first  to  retard  the  flow, 
but  later  to  greatly  increase  it,  thus  virtually  concentrating  a  large  part  of  the 
precipitation  into  a  few  hours.  The  Raritan  River,  with  a  catchment  area  of 
879  square  miles,  reached  its  maximum  flow  in  about  16  hours,  the  rate 
being  68  cubic  feet  per  second  per  square  mile.  If  3  inches  represent  the 
precipitation  during  this  time,  the  flow  would  then  be  estimated,  according  to 
the  method  of  Art.  69,  at  3  X  .  50  =  1.5  inches  in  16  hours,  or  2.25  inches 
in  24  hours,  equal  to  61  cubic  feet  per  second  per  square  mile.  The  Passaic 
with  a  drainage-area  of  822  square  miles  reached  its  maximum  in  44  hours, 
and  yielded  only  22  cubic  feet  per  second  per  square  mile,  the  slowness  of 
the  rise  and  low  maximum  rate  being  due  to  extensive  flats  along  the  river. 
Estimating  this  in  a  similar  manner,  the  rainfall  would  be  the  total  amount, 
or  4.3  inches,  and  the  flow  equal  to  4.3  X  .50  x  f-|  X  27  =  31.6  cubic  feet 
per  second  per  square  mile.  These  two  examples  serve  to  show  that,  while 
all  estimates  of  flood-flows  will  be  only  roughly  approximate,  yet  the  method 
given  will  lead  to  more  rational  results  than  the  application  of  any  formula. 

Data  of  the  rise  and  flow  of  other  New  Jersey  streams  during  this  flood 
are  given  on  the  next  page.  They  well  illustrate  the  importance  of  taking 
account  of  features  of  a  watershed  other  than  mere  extent  of  area. 

*  Trans.  Am.  Soc.  C.  E.,  1891,  xxiv.  p.  431. 

f  Report  New  York  State  Engineer,  1894,  p.  387. 

|  See  Report  Geological  Survey  of  New  Jersey,  1896. 


FLOW   OF  STREAMS. 


The  decrease  in  flow  with  increase  in  the  time  required  to  reach  a  maxi- 
mum is  quite  regular,  with  the  exception  of  the  Pequest,  a  stream  having  very 
large  surface  storage. 


Stream 

Approximate 
No.  of  Hours 
from  Beginning 
to  Maximum 
Flow. 

Discharge, 
Cubic  Feet  per 
Second  per 
Square  Mile. 

Drainage-  area, 
Square  Miles. 

7 

115 

48 

South  Branch  

8 

Il-i 

67 

IO 

84 

18 

II 

QQ 

70 

15 

ia 

I5S 

16 

68 

87Q 

16 

65 

285 

Rockaway  

16 

40 

118 

Ramapo.  

24 

C.A 

160 

Passaic  •  • 

4.4. 

22 

870 

The  flood  on  the  Sudbury  River  caused  by  the  great  rain-storm  in  New 
England  in  February,  1886,  is  described  by  Mr.  FitzGerald  in  a  paper  before 
the  American  Society  of  Civil  Engineers.*  The  total  rainfall,  including  snow 
equivalent  to  2  inches  of  rain,  from  7  P.M.,  Feb.  10,  to  midnight,  Feb.  13, 
was  estimated  at  6.64  inches,  of  which  about  5.08  inches  flowed  off,  or  about 
75  per  cent.  The  maximum  rain  in  24  hours  was  about  3  inches,  and  the 
maximum  rate  of  flow  was  1.54  inches  per  24  hours,  or  about  one-half  that 
of  the  rainfall.  The  size,  of  the  drainage-area  is  about  78  square  miles,  and 
the  topography  an  average  for  New  England  watersheds.  On  a  neighboring 
stream  of  only  6.4  square  miles  of  watershed  the  maximum  rate  of  flow  was 
1.801  inches  per  24  hours.  The  two  rates  were  thus  nearly  the  same,  as  the 
heavy  rainfall  was  of  sufficient  duration  to  affect  fully  the  larger  watershed. 

TOTAL    FLOW    FOR   VARIOUS   PERIODS   OF   TIME. 

73.  Statistics  of  Stream-flow. — Valuable  records  of  run-off  are  avail- 
able for  a  number  of  streams  in  the  Eastern  States  that  have  been  used 
or  considered  as  a  source  of  supply,  but  aside  from  these  the  informa- 
tion is  meager.  The  most  valuable  of  the  available  data  are  sum- 
marized in  Table  No.  16,  in  which  are  given  the  average  yearly,  the 
minimum  yearly,  and  the  seasonal  flows,  with  corresponding  rainfalls. 

The  characteristics  of  the  various  watersheds  are  briefly  as  follows : 
The  Sudbury,  Cochituate,  and  Mystic  have  been  for  many  years  the 
sources  of  Boston's  water-supply.  The  Sudbury  watershed  is  hilly 
and  has  steep  slopes,  but  contains  some  large  swamps;  the  Cochituate 
watershed  is  flat  and  sandy,  while  the  Mystic  is  of  an  intermediate 
character.  All  have  a  very  considerable  percentage  of  forest  area. 
The  Connecticut  River  has  a  rugged  watershed  with  about  half  the  area 
*  Trans.  Am.  Soc.  C.  E.,  1891,  xxv.  p.  253. 


THE    TOTAL   RUN-OFF. 


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CO 

o 
co 

M 

CO      Tf 

rf     O 

°.     w. 
M"     t^ 

M 

IT 

0 

in 

O 
N 

CO 

a 

; 

j 

i 

*m        * 

j 

! 

o, 
8 

9 

Q 

5 

Sudbury.  .  . 

Cochituate. 
Mystic  

Connecticut 

T3 

3 

-H-     E 

C      u, 
0       <u 

II 

Genesee.  .  . 
Passaic.  .  .  . 

Perkiomen. 
Tohickon.. 

Neshaminy. 

Potomac..  . 
Savannah.. 

Des  Plaines 

M 
V} 

s 

IN 

1) 

O, 

a 
D 

80  FLOW  OF  STREAMS. 

fallow  or  timbered.  The  Croton  is  a  hilly  watershed  with  about  30 
per  cent  timbered.  The  upper  Hudson  is  a  rugged  mountainous 
watershed  with  about  70  per  cent  in  forest.  The  Genesee  has  moderate 
slopes  and  only  25  per  cent  of  forest  area.  The  Passaic  has  58  per 
cent  of  forest  area  and  is  of  varied  topography,  some  parts  being  very 
hilly  and  others  quite  flat.  The  Perkiomen,  Tohickon,  and  Neshaminy 
are  small  streams  near  Philadelphia.  Their  watersheds  are  hilly,  with 
elevations  from  250  to  1000  feet  high,  and  contain  areas  of  timber  and 
waste  land  equal  to  25  per  cent  in  the  case  of  the  first  two  streams, 
and  7  per  cent  in  the  case  of  the  Neshaminy.  The  Potomac  watershed 
has  steep  mountainous  slopes  with  a  large  proportion  of  forest  and 
waste  land.  The  Savannah  lies  mostly  in  a  rolling  country  with  a 
considerable  percentage  of  forest  area.  The  Des  Plaines,  a  stream 
near  Chicago,  has  a  watershed  of  very  flat  slopes,  a  considerable 
amount  of  low  swampy  land,  and  very  little  forest  area.  The  water- 
shed of  the  upper  Mississippi  is  heavily  wooded  and  nearly  level. 
The  percentage  of  water-surfaces  on  the  various  areas  is,  for  the 
Sudbury  about  3  per  cent,  the  Cochituate  7.6  per  cent,  the  Mystic 
3  per  cent,  the  Croton  1.8  per  cent,  the  upper  Mississippi  18  per  cent, 
and  for  the  others  less  than  I  per  cent. 

The  very  considerable  variation  in  average  percentage  flowing  from 
the  different  watersheds,  due  to  differences  in  climate  and  physical 
features,  is  quite  marked. 

74.  Minimum  Yearly  Flow. — From  the  data  given  in  the  table  it 
appears  that  the  least  yearly  run-off  for  some  of  the  streams  of  the 
upper  Atlantic  coast  region  is  only  9  or  10  inches,  or  about  one-half 
the  average  run-off.  For  the  Genesee  it  is  only  6.67  inches.  The 
data  for  the  Massachusetts  streams  cover  a  very  great  drought  and  are 
considered  by  those  of  experience  as  being  safe  for  future  estimates  in 
that  region.  That  such  low  values  of  run-off  have  not  occurred  on 
many  of  the  other  watersheds  appears  to  be  mainly  due  to  the  fact  that 
the  rainfall  has  never  been  so  low  at  those  places  during  the  period 
covered  by  the  records.  There  seems  to  be  no  reason,  however,  why 
it  may  not  at  some  future  time  be  equally  low. 

It  is  important  to  note  that  in  dry  years  the  proportion  of  the  pre- 
cipitation flowing  off  is  much  smaller  than  the  average,  and,  in  general, 
the  smaller  the  rainfall  the  smaller  is  likely  to  be  the  proportion  running 
off.  In  California,  for  example,  it  is  estimated  by  Le  Conte  *  that  in 
the  vicinity  of  San  Francisco,  when  the  yearly  rainfall  is  10,  20,  30, 

*  Trans.  Am.  Soc.  C.  E.,  1892,  xxvn.  p.  292. 


THE    TOTAL   RUN-OFF. 


8l 


40,    or   50  inches,    the  flow  is   approximately  0.5,   2,   9,    18,   and  30 
inches,  respectively.      The  percentages  thus  vary  from  5  to  60. 

Like  yearly  rainfalls  will  not  necessarily  give  like  flows,  as  the 
amount  flowing  depends  much  upon  the  distribution  of  the  rain 
throughout  the  year,  and  upon  whether  it  is  concentrated  in  a  few  large 
storms  or  is  more  evenly  distributed.  The  least  flow  for  a  given  yearly 
rain  is  caused  by  a  combination  of  unfavorable  conditions,  and  in 
making  estimates  such  least  flows  are  the  ones  to  be  considered. 
Fig.  14  represents  by  the  shaded  portion  approximately  the  least  flows 


s^ 


/o 


2O 


3O 
Jf7 


60 


FIG.  14. — PROBABLE  MINIMUM  YEARLY  STREAM-FLOW. 

for  given  rainfalls  for  most  of  the  streams  represented  in  Table  No.  16, 
as  determined  from  the  detailed  statistics.  The  dotted  portions  are 
extensions  of  the  curves  beyond  the  field  covered  by  the  data.  The 
upper  limit  represents  such  streams  as  the  Connecticut,  Passaic,  and 
Tohickon,  and  the  lower  curve  the  Cochituate,  while  the  curves  for 
most  of  the  other  streams  fall  somewhere  between  these  limits.  The 
upper  Hudson  falls  somewhat  above  the  diagram,  and  the  Genesee 
below.  The  Des  Plaines  and  upper  Mississippi  fall  far  below.  In 
some  cases  the  curve  for  a  stream  will  be  low  at  one  end  and  high  at 
the  other,  as,  for  example,  the  curve  for  the  Mystic.  For  very  low 
rainfalls  this  watershed  gives  as  low  a  yield  as  the  Cochituate,  but 
for  rainfalls  of  40  or  50  inches  the  run-off*  is  much  greater. 

According  to  this  diagram,  the  least  run-off*  to  be  expected  from 
ordinary  watersheds  in  the  Eastern  States  for  a  rainfall  of,  say,  40  inches 
would  probably  be  somewhere  between  \2\  and  1 8  inches,  depending 
upon  the  character  of  the  watershed.  For  a  rainfall  of  30  inches  the 
least  flow  to  be  expected  would  be  between  ?J  and  12 £  inches. 


82 


FLO  IV   OF  STREAMS. 


For  other  parts  of  the  United  States  having  about  the  same  general 
distribution  of  rainfall,  these  data  and  curves  will  be  of  assistance  in 
making  approximate  estimates.  The  effect  of  varying  yearly  rainfalls 
will  at  least  be  similar  to  that  shown  by  the  curves  in  the  figure,  and 
with  this  kept  in  mind  even  one  or  two  years  of  gaugings  will  be  of 
much  value.  For  localities  with  a  much  different  distribution  of  rainfall 
than  in  the  Eastern  States  it  will  be  necessary  to  consider  carefully 
this  distribution  as  shown  below. 

75.  Monthly  and  Seasonal  Flow.  —  The  average  monthly  flow, 
together  with  the  average  monthly  rainfall,  is  shown  for  several  streams 
in  the  diagram  Fig.  15.  There  are  also  given  in  Table  No.  16  the 


1; 


Crofon 


/\ 


Cocfitftserff 


Perk/omen 


I* 


Connect/cut 


7 
6 
S 
4- 
3 

a 
o\ 

\* 


ftun-off 


FIG.  15  —  AVERAGE  MONTHLY  STREAM-FLOW. 

average  rainfall,  run-off,  and  percentage  running  off  for  the  six  montns 
from  June  to  November,  and  for  the  six  months  from  December  to 
May,  the  former  period  being  in  general  the  six  months  of  least  pro- 
portionate flow,  and  the  latter  that  of  greatest  flow.  From  these 
figures  and  diagrams  the  small  value  of  summer  rains  in  furnishing 
water  to  the  streams  is  evident. 

A  detailed  analysis  for  the  several  years  shows  that  what  was  true 
for  yearly  rainfall  is  also  true  for  seasonal,  namely,  that  the  less  the 
rainfall  the  less  the  percentage  flowing  off.  The  relation  between  rain- 
fall and  run-off  is  represented  approximately  by  the  curves  in  Fig.  16, 
which  is  constructed  similarly  to  Fig.  14,  using  here  seasonal  rainfall 
and  seasonal  flow.  The  diagrams  represent  by  the  shaded  portions 
minimum  values  of  run-off  which  may  be  expected  for  various  seasonal 


THE    TOTAL   RUN- OFF.  83 

rainfalls  for  the  same  streams  as  are  represented  in  Fig.  14.  They  will 
be  of  some  service  in  estimating  stream-flow  where  the  rainfall  has  a 
somewhat  different  distribution  than  upon  the  watersheds  in  question. 

Detailed  statistics  pertaining  to  the  Sudbury  River  for  the  years 
from  1879  to  1884  are  here  appended  in  Table  No.  17,  p.  84.*  They 
furnish  a  good  illustration  of  the  variation  in  stream-flow  from  month  to 
month,  and  cover  the  most  critical  period  so  far  observed  in  that  region. 


20 


YY/nfer 


Summer* 


\ 


\'° 

I- 


a? 


JO 


/O 


^o 


FlG.  16. — PROBABLE  MINIMUM  SEASONAL  STREAM-FLOW. 

They  form  the  basis  of  storage  computations  mentioned  in  Chapter  XV. 
The  effect  of  the  difference  in  the  distribution  of  the  rainfall  in  the 
years  1880  and  1882  should  be  noted.  Compare  also  the  data  for 
1880  and  1883. 

76.  Estimates  of  Flow. — The  data  in  the  preceding  articles  will 
enable  fairly  close  estimates  to  be  made  of  the  amount  of  run-off  for 
streams  in  the  Eastern  States  or  for  regions  of  like  characteristics. 
For  other  regions  rough  estimates  may  still  be  made  by  a  judicious 
use  of  the  data  in  connection  with  rainfall  statistics,  and  by  a  careful 
consideration  of  the  influences  affecting  evaporation  and  percolation. 

In  any  given  case  the  years  for  which  estimates  are  required  are 
those  of  least  flow;  and  since  it  is  not  usually  desirable  to  have 
impounding-reservoirs  for  water-supply  purposes  drawn  below  the 
high-water  line  for  more  than  two  or  three  years  at  a  time,  the  period 
covering  the  two  or  three  driest  consecutive  years  is  all  that  need  be 
investigated.  Rainfall  data  for  such  periods  can  be  obtained  from 
Chapter  IV,  and  also  the  average  distribution  during  the  two  parts  of 
the  year  (Table  No.  6,  page  47).  This  being  known,  approximate 
estimates  of  the  seasonal  flows  can  then  be  made  from  the  diagrams  of 
Figs.  14  and  16,  making  allowance  as  far  as  possible  for  differing  con- 
ditions. In  making  use  of  these  diagrams  it  should  be  borne  in  mind 


*Mass.  Board  of  Health  Reports. 


84 


FLOW  OF  STREAMS. 


that  the  minimum  curves  represent  extreme  conditions,  such  as  would 
obtain  for  a  single  season  or  a  single  year  only.  In  considering  a 
number  of  consecutive  years  or  seasons  the  values  given  by  these 


TABLE    NO.  17. 

RAINFALL   RECEIVED   AND    COLLECTED    ON   THE    SUDBURY    RIVER   WATERSHED, 

1879-1884. 


1879. 

1880. 

1881. 

Months. 

Rainfall. 

Rainfall 
Collected. 

Per  cent 
Collected. 

Rainfall. 

Rainfall 
Collected. 

Per  cent 
Collected. 

13 

c 

Rainfall 
Collected. 

Per  cent 
Collected. 

2  48 

I    25 

CQ   A. 

•3  .  cn 

2    OO 

56  O2 

5.56 

O    74 

13    31 

3   56 

2  .  76 

77  .  4 

•3    08 

2.o8 

74   Q2 

4    65 

2    4Q 

53  .  62 

March                   

514. 

416 

go    Q 

•2      -32 

2    45 

73  .  Q3 

5    73 

7    14 

124   64 

April               

4.  72 

5    38 

1  14..  T 

•7  .  II 

2    O2 

64  Q7 

2.OO 

2   67 

1  33    44 

May  

1.58 

1  .90 

125.8 

1.84 

O.Q2 

40.05 

3.51 

I.  72 

49  •  03 

3    7Q 

O.7I 

18.8 

2    14. 

O.  3O 

14.  16 

5.4O 

2    qo 

42.8O 

Tulv 

3   03 

o  28 

7.  1 

6.27 

O.  32 

5  .02 

2.  35 

O   4Q 

2O    08 

6    51 

O   71 

10.8 

4-OI 

O.  21 

5  .  20 

1.36 

o  26 

IQ   45 

T.88 

O.  24 

I2-Q 

1.  60 

o.  14 

8.64 

2.62 

O.  34 

I3.OI 

0.81 

O.  13 

15.6 

a.  74 

o.  18 

4.85 

2.  96 

O.  33 

1  1.  2O 

2.68 

o  36 

13    2 

1  .  7Q 

O    35 

IQ    85 

4OQ 

o  68 

1  6  66 

434 

o  83 

19   O 

2.83 

O    31 

1  1    05 

3    06 

i  38 

34    Q3 

Total  and  averages. 

41.42 

18.76 

45-3 

38.18 

12.  18 

3I-9I 

44.17 

20.57 

46-56 

1882. 

1883. 

1884. 

Months. 

Rainfall. 

Rainfall 
Collected. 

Per  cent 
Collected. 

Rainfall. 

Rainfall 
Collected. 

Per  cent 
Collected. 

Rainfall. 

Rainfall 
Collected. 

Per  cent 
Collected. 

5  .Q5 

2  .  21 

37  .  IQ 

2   8l 

o.  60 

21    25 

5  .OQ 

I    78 

3-1   QI 

455 

3    87 

85  18 

3   87 

i  66 

43   O5 

6    55 

4.  74 

72   45 

March     

2   65 

5   06 

191   16 

I    78 

2    87 

l6l  .42 

A.  72 

6   75 

143   06 

1.82 

I    5O 

82    OQ 

I    85 

2  •  11 

126.  27 

4   41 

4.  QO 

III  .82 

May 

5O7 

23O 

AC     A& 

i  67 

347 

I      8j. 

52    Q7 

i  66 

o  91 

54    87 

2AQ 

Or  2 

21    58 

345 

O72 

20  86 

Tulv 

I    77 

O    15 

8  70 

2  68 

O    21 

7  68 

3    67 

o  40 

10  89 

1.67 

O.  IO 

5  .QI 

0.74 

O.  14 

IQ  06 

4.65 

0.46 

Q.SI; 

8.74 

O.  53 

16.O5 

1.52 

o  16 

10.  36 

0.86 

O.O8 

8.8) 

2.O7 

DJ 
O    53 

0 

25  .  74 

5    60 

033 

5Q2 

2    48 

O    15 

5.o8 

I    15 

o  36 

31    51 

i  81 

O    35 

IQ    52 

2.65 

O    TO 

1  1    44 

2    3O 

o.  56 

24.45 

3    re 

O    35 

972 

c  .  17 

I    65 

^1    QI 

Total  and  averages. 

39-39 

I8.IO 

45-95 

32.78 

11.19 

34-13 

47.14 

23.78 

50.46 

THE    TOTAL   RUN- OFF.  85 

curves  should  therefore  be  used  for  but  one  or  two  such  periods,  much 
more  liberal  values  being  assumed  for  the  remainder,  or  for  the 
average. 

If  the  watershed  contains  large  areas  of  water-surface,  it  is  important 
that  proper  allowance  be  made  for  the  evaporation  from  such  surfaces, 
data  for  which  are  given  in  Chapter  V. 

77.  Effect  of  Lakes  and  Ponds  on  Stream-flow.  — The  result  found  by 
the  preceding  method  takes  no  account  of  the  effect  of  lakes  and  ponds 
acting  as  storage-reservoirs ;  the  calculations  would  indeed  often  indicate 
a  negative  flow  due  to  evaporation  from  excessive  areas  of  water-sur- 
face, when  in  reality  the  flow  is  rendered  more  steady  and  continuous 
by   such   ponds,    although   the  total  yield   may    be   much   diminished 
thereby.      This  equalizing  effect  of  natural  ponds  depends  upon  the 
amount  their   flow-line   can   be   lowered,    that  is,    upon  the  available 
storage  contained  therein ;  and  can  be  more  easily  and  logically  taken 
account    of  in    connection    with    the    question    of    artificial    storage. 
(Chapter  XV.) 

78.  Example  of  Estimate  of  Flow. — As  an  example,  let  it  be  required  to 
estimate  the  yield  per  square  mile  of  a  watershed  containing  10  per  cent  of 
water-surface,  having  moderate  slopes,  and  about  two-thirds  in  meadows  and 
under  cultivation,  the  remainder  being  forest  area.      Suppose  the  rainfall  dis- 
tribution  and   evaporation  to  be  as  given  for  Davenport,    Iowa,   in  Tables 
Nos.  6  and   u,  pp.  45  and  56;  but  for  safety  we  will  take  0.55,  0.65,  and 
o.  70  as  the  ratios  to  the  average,  of  the  rainfalls  for  the  one,  two,  and  three 
driest  years  respectively,  the  average  rainfall  being  33.3  inches.     Assuming  the 
distribution  of  the  rainfall  in  dry  years  to  be  the  same  as  the  average,  we  will 
have  the  following  rainfalls  in  each  six  months  of  the  three  consecutive  years, 
putting  for  convenience  the  driest  year  second  and  the  wettest  year  first : 

First  Year.  Second  Year.  Third  Year. 

Total 26.5  inches  18.3  inches  25.1  inches 

December-May n.i       "  7.7       "  10.5       " 

June-November 15.4       4i  10.6       "  14.6 

By  the  aid  of  Fig.  16  we  may  then  estimate  the  flow  for  each  six- month 
period.  On  account  of  the  flat  slopes  and  agricultural  character  of  the 
country,  the  area  in  question  would  not  be  classed  higher  than  the  poorest  of 
those  represented  in  the  diagram.  For  the  driest  year  we  may  therefore 
assume  the  flow  according  to  the  lowest  curves,  giving  about  4  inches  and 
o  inch  as  the  least  flows  to  be  expected  for  the  two  six-month  periods  of  the 
second  year.  For  the  third  year,  with  rainfalls  of  10.5  and  14.6  inches  for 
the  two  seasons,  we  would  have  run-offs  of  perhaps  5^  inches  and  i  inch 
respectively;  and  for  the  first  year,  allowing  somewhat  more  liberal  figures, 
we  may  estimate  the  flow  at  6^-  and  2  inches. 

The  run-off  for  the  driest  year  is  so  small  that  it  is  largely  dependent 
upon  ground-storage  and  upon  the  occurrence  of  a  part  of  the  rainfall  in 
heavy  storms.  That  such  small  flows  may  be  expected  as  are  here  given 


86 


FLOW   OF  STREAMS. 


can  be  seen  by  a  reference  to  the  data  for  the  Des  Plaines  in  Table  No.  16. 
The  flow  of  this  stream,  it  may  be  noted,  ceased  altogether  for  a  time  in 
nearly  every  summer  during  the  observations;  and  furthermore,  of  the  3.19 
inches  flowing  in  the  year  1895,  1.80  inches  flowed  in  the  month  of  Decem- 
ber, leaving  but  1.39  inches  for  the  previous  eleven  months. 

So  far  the  estimates  are  for  land-surface  only,  or  for  a  watershed  with  in- 
significant water-areas.  To  these  values  must  now  be  added  or  subtracted 
the  excess  or  deficiency  of  rainfall  over  evaporation  from  the  10  per  cent  of 
water-surfaces,  the  evaporation  data  being  taken  from  Table  No.  n,  Chapter 
V.  This  gives  a  negative  flow  in  some  cases,  which  means  that  evaporation 
from  the  lakes  and  ponds  exceeds  the  natural  flow  from  the  area.  The  various 
items  are  recapitulated  in  Table  No.  18. 

To  estimate  the  distribution  of  the  stream-flow  throughout  the  various 
months  it  is  sufficiently  close,  and  as  accurate  as  the  above  method  of  estima- 
tion warrants,  to  assume  the  excess  of  winter's  flow  over  summer's  flow  to  be 
all  concentrated  in  the  four  months,  January  to  April,  and  as  uniformly  dis- 
tributed over  these  months.  The  remainder  may  be  assumed  as  uniformly 
distributed  over  the  entire  year.  As  regards  the  necessary  storage- volume, 
the  exact  distribution  of  the  flow  whenever  it  exceeds  or  falls  short  of  the 
average  consumption  is  of  no  consequence,  the  only  matters  of  importance 
being  the  total  amount  of  excess  or  deficiency  and  the  time  when  such  excess 
or  deficiency  begins.  Where  a  negative  flow  occurs  it  is  subtracted  from  the 
flow  for  the  succeeding  period,  and  the  remainder  assumed  as  flowing  in  the 
four  months  of  January  to  April.  The  results  are  given  in  Table  No.  18,  in 
gallons  per  day  for  the  two  periods,  January  to  April,  and  May  to  December. 

Instead  of  using  general  percentages  for  the  rainfall  for  dry  periods,  and 
an  average  distribution  of  the  rainfall,  the  actual  rainfalls  might  have  been 
used.  In  either  case,  however,  the  results  must  be  looked  upon  as  but  a 
rough  indication  of  what  the  flow  is  likely  to  be. 

TABLE    NO.    18. 

ESTIMATE  OF  FLOW   FOR   THREE    DRY    YEARS    FROM    ONE   SQUARE    MILE   OF    WATERSHED 
CONTAINING   TEN    PER    CENT    OF    WATER-SURFACES. 


Period. 

1 
1 
K 

Inches. 

Flow  from 
Land-surfaces. 

Flow  from  Water- 
surfaces. 

Net  Flow. 

Total. 
Inches. 

90* 
Inches. 

Evap- 
oration. 

Inches. 

Rainfall  Minus 
Evaporation. 

Inches  each 
Six  Months. 

Gallons  per  Day. 

Total. 
Inches. 

10* 

Inches. 

Jan.-Apr. 

May  -Dec. 

First  Year: 
Dec.  to  May.  .  . 
June  to  Nov.... 

Second  Year: 
Dec.  to  May.  .  . 
June  to  Nov.  .  .. 

Third  Year: 
Dec.  to  May.... 
June  to  Nov.... 

II.  I 
15-4 

7-7 
10.6 

10.5 
I4-6 

6.5 

2.0 
4.0 

o 

5-5 

I.O 

5.85 
I.  80 

3-60 
O 

4-95 
O.QO 

ii.  6 

27.4 

ii.  6 

27.4 

11,6 
27.4 

-   0.5 
—  12.0 

-  3-9 
-16.8 

—   i.i 

-12.8 

—  0.05 

—  1  .  20 

-0-39 

-1.68 

—  O.II 

-1.28 

5-80 
0.60 

3-21 
-1.68 

4.84 
-0.38 

800,000 

60,000 
O 
O 

460,000 

450,000 

LITER  A  TURE. 


LITERATURE. 

1.  Herschel.     The  Gauging  of  Streams.     Trans.  Am.   Soc.  C.  E.,    1878, 

vn.  p.  236. 

2.  Report  of  Committee  on  the  Gauging  of  Streams.     Proc.  Am.  Soc.  C.  E., 

1879,  v.  p.  109.     Contains  table  on  maximum  and  minimum  flow. 

3.  Fteley.     Flow  of  Sudbury  River,   Massachusetts,  for  the  years  1875  to 

1879.     Contains  data  on   maximum  and  minimum   flow.     Trans. 
Am.  Soc.  C.  E.,  1  88  1,  x.  p.  225. 

4.  Brackett.     Rainfall  Received  and  Collected  on  the  Watersheds  of  Sudbury 

River,  and  Cochituate  and  Mystic  Lakes.     Jour.  Assn.  Eng.    Soc., 
1886,  v.  p.  395. 

5.  FitzGerald.     Yield  of  the  Sudbury  River  Watershed  in  the  Freshet  of 

February  10-13,  1886.     Trans.  Am.  Soc.  C.  E.,  1891,  xxv.  p.  253. 

6.  Report  of  the  Committee  on  the  Cause  of  the  Failure  of  the  South  Fork 

Dam.     Trans.  Am.  Soc.  C.  E.,  1891,  xxiv.  p.  431. 

7.  FitzGerald.     Rainfall,  Flow  of  Streams,  and  Storage.     Trans.  Am.  Soc. 

C.  E.,  1892,  xxvii.  p.  304. 

8.  Babb.     Hydrography  of  the  Potomac  Basin.     Trans.  Am.  Soc.  C.  E., 

1892,  xxvii.  p.  21. 

9.  Babb.     Rainfall  and  Flow  of  Streams.     Trans.  Am.  Soc.  C.  E.,    1893, 

xxvin.  p.  323. 

10.  Mead.     The  Hydrogeology  of  the  Upper  Mississippi  Valley  and  of  some  of 

the  Adjoining  Territory.      Jour.  Assn.  Eng.  Soc.,  1894,  xm.  p.  329. 

11.  Vermeule.     Report  on  Water-supply.     Geolog.  Survey  of  N.  J.,  1894,111. 

Data  relating  to  many  streams  are  here  brought  together  and  discussed. 

12.  Geolog.  Survey  of  New  Jersey,  1896,  p.  257.     The  floods  of  Feb.  6,  1896. 

13.  (a)  Newell.     Results  of  Stream  Measurements.     U.   S.  Geolog.  Survey, 

1892-3,  p.  89. 
(3)  Leverett.     The  Water  Resources  of  Illinois.     U.  S.  Geolog.  Survey, 

1895-6,  Part  II,  p.  701. 

Besides  the  above-named  papers,  the  reports  of  the  Survey  since 
1888,  the  Bulletins,  and  the  Water-supply  and  Irrigation  Papers  con- 
tain much  valuable  information  relating  to  the  hydrography  of  the 
United  States. 

14.  Report  State  Engineer,  N.  Y.,  1894,  p.  387.     The  flood  in  the  Chemung 

River.     The  reports  for  1895  and  1896  contain  data  relating  to  the 
upper  Hudson  and  the  Genesee. 

15.  Johnston.      Data  Pertaining  to  Rainfall  and  Stream-flow.     Jour.  W.  Soc. 

Eng.,   1896,  i.  p.  297.      Relates  chiefly  to  the  Des  Plaines  River. 
1  6.   Report  Chief  of  Engineers,  U.   S.  A.,  1896,  p.  1843.      Data  relating  to 

the  upper  Mississippi. 
17.   Wegmann.     The  Water-supply  of  the  City  of  New  York.     N.  Y.,  1896. 

Data  relating  to  the  Croton. 
1  8.   Annual  Reports  of  the  Water  Bureau  of  Philadelphia.     Contain  complete 

.     data  relating  to  the  Perkiomen,  Tohickon,  and  Neshaminy. 
1  9.   Reports  of  the  Boston  Water  Board  and  of  the  Metropolitan  Water  Board 

(Boston).     Monthly  data  relating  to  the  Sudbury,  Cochituate,  and 

Mystic. 
20.   Chamier.     Capacities  Required  for  Culverts  and  Flood  Openings.     Proc. 

Inst.  C.  E.,  1898,  cxxxiv.  p.  313. 


88  FLO  W  OF  STREAMS. 

21.  New  York  State  Engrs.     Report  on  Barge  Canal,  1901.     Data  on  Min. 

and  Max.  flows.     App.  vm.  pt.   14,  p.  844. 

22.  Lippincott   and  Bennett.     Relation  of  Rainfall  to  Run-off  in  California. 

Eng.  News,   1902,  XLVII.  p.  467. 

23.  U.  S.  Geological  Survey;  Water-supply  and  Irrigation  Papers.     Many  of 

these  contain  very  valuable  data  on  rainfall,  run-off  and  flood  dis- 
charge. Of  special  value  are  Papers  Nos.  147  and  162  by  C.  E. 
Murphy  on  destructive  floods  in  1904  and  1905  ;  also  Paper  No.  80 
by  G.  W.  Rafter  on  the  Relation  of  Rainfall  to  Run-off. 

24.  Hoyt.      Comparison  Between  Rainfall  and  Run-off  in  the  Northeastern 

United  States.     Trans.  Am.  Soc.  C.  E.,  1907,  LIX.  p.  431. 


CHAPTER    VII. 

GROUND-WATER. 

GENERAL   CONSIDERATIONS. 

79.  Occurrence  of  Ground-water. — In  Chapter  V  it  was  shown  that 
water  precipitated  upon  the  earth's  surface  in  any  form  is  disposed  of 
in  three  ways:  by  evaporation,  by  surface-flow,  and  by  percolation. 
In  Chapter  VI  the  stream-flow  was  shown  to  include  both  the  surface- 
water  and  the  water  of  percolation.  In  the  present  chapter  it  is  pro- 
posed to  deal  with  the  last-mentioned  portion  more  in  detail,  as  to  its 
quantity,  movement,  and  availability  as  a  direct  source  of  supply. 

Percolating  water  that  escapes  beyond  the  reach  of  vegetation  must, 
in  obedience  to  the  law  of  gravitation,  pass  on  downward  until  it 
reaches  an  impervious  layer  of  some  sort.  The  immediate  impervious 
stratum  is  the  surface  of  the  water  which  has  preceded  it  and  which 
has  in  past  ages  filled  every  pore  and  crevice  of  the  earth's  crust  up  to 
a  certain  level  at  which  the  escape  of  the  water  laterally  becomes  equal 
to  the  addition  from  percolation.  The  accumulation  of  water  which 
thus  exists  in  the  ground  is  called  ground-water,  and  its  surface  the 
ground-water  level  or  the  water-table. 

In  limestone  regions  it  is  sometimes  the  case  that  quite  large 
streams  are  found  flowing  underground,  and  large  cavernous  spaces 
may  be  converted  into  underground  lakes  of  considerable  size,  as  in 
the  great  caverns  of  Indiana  and  Kentucky.  Such  bodies  of  water 
are,  however,  rarely  available  for  a  water-supply,  and  it  may  be  taken 
as  a  safe  rule  that  for  ground-water  supplies  dependence  must  be 
placed  upon  the  water  which  percolates  into  and  flows  through  the 
pore-spaces  in  soils  and  rocks,  the  amount  of  which  is  strictly 
dependent  upon  the  rainfall  and  the  laws  of  hydraulics  that  govern  the 
flow. 

89 


QO  GR  O  UND-  WA  TER. 

80.  General  Form  of  the  Water-table. — Under  the  action  of  gravity 
the  surface  of  the  ground-water  always  tends  to  become  a  level  surface, 
and  as  long  as  a  supply  is  maintained  through  percolation  there  will 
be  a  continual  lateral  flow  which  will  on  the  average  be  equal  to  the 
percolation.  In  surface  streams  a  very  slight  inclination  is  sufficient 
to  cause  a  rapid  movement  of  water,  but  in  the  ground  the  resistance 
to  movement  is  so  great  that  a  relatively  steep  gradient  is  necessary  to 
maintain  even  a  very  low  velocity. 

If  we  imagine  the  ground  to  be  throughout  of  uniform  porosity,  the 
ground- water  surface  will  conform  in  general  outline  to  the  ground- 
surface,  but  with  less  variations.  Such  an  ideal  condition  is  repre- 
sented in  Fig.  17.  At  the  margin  of  streams  the  level  of  ground-  and 


FIG.  17. — GENERAL  RELATION  OF  SURFACE  OF  GROUND-WATER  TO    THE  SURFACE 

OF  THE  EARTH. 

surface-waters  will  coincide.  Passing  back  from  the  stream  the 
ground-water  level  will  gradually  rise,  but  at  a  less  rate  than  the 
ground-surface,  then  descend  again  into  another  depression,  etc.  In 
the  valley  there  is  also  a  fall  parallel  to  the  stream,  corresponding  to 
that  of  the  surface-water,  and  the  direction  of  flow  will  be  towards  and 
slightly  down  the  stream  in  the  line  of  greatest  declivity. 

Increased  percolation  will  raise  the  level  of  the  ground-water,  but 
less  rapidly  at  the  outlet  than  elsewhere,  thus  increasing  the  gradient 
and  consequently  the  flow.  During  a  period  of  drought  the  flow  will 
continue  at  a  slower  and  slower  rate,  due  to  decreased  gradient,  until 
the  water  ceases  to  flow  laterally  into  the  stream ;  the  stream  then 
becomes  dry,  and  the  flow  continues  at  a  slow  rate  parallel  to  the 
valley  and  entirely  underground.  Thus  in  a  region  where  the  forma- 
tions are  very  porous  and  where  the  slopes  are  very  steep,  large 
streams  will  disappear  and  flow  for  long  distances  underground. 

In  any  actual  instance  the  ground  is  usually  far  from  having  the 
uniform  porosity  as  assumed  in  the  ideal  example  above ;  and  the  areas 
to  be  studied  will  ordinarily  consist  of  alternating  strata  of  coarse 
porous  materials,  and  of  fine  and  more  or  less  impervious  deposits. 


POROSITY  OF  SOILS.  91 

In  general  the  change  from  coarse  to  fine  material  in  the  direction 
of  flow  will  be  accompanied  by  an  increased  gradient  in  the  ground- 
water  level  owing  to  the  increased  resistance;  and  conversely.  If  the 
gradient  necessary  to  carry  the  quantity  of  water  reaching  the  section 
in  question  is  greater  than  the  surface  gradient,  an  overflow  to  the  sur- 
face takes  place,  thus  giving  rise  to  a  marsh  or  to  a  surface  stream. 
Overflows  thus  occur  frequently  at  the  foot  of  hills  where  the  ground- 
water  surface  is  apt  to  be  at  a  very  small  depth. 

Variations  in  ground-water  level  take  place  comparatively  slowly, 
following  gradually  the  variations  in  yearly,  seasonal,  and  briefer 
periods  of  rainfall.  Near  streams  and  in  lowlands  the  level  varies 
little,  being  fixed  largely  by  the  level  of  the  adjacent  surface-water. 
At  higher  points  in  the  water-table  the  level  is  subject  to  correspond- 
ingly great  fluctuations,  often  many  feet  in  extent.  In  porous  material 
where  slopes  are  small  the  variations  are  small. 

81.  Porosity  of  Soils. — All  soils  and  rocks  near  the  surface  of  the 
earth  are  capable  of  absorbing  more  or  less  water. 

If  the  particles  of  a  body  of  sand  or  soil  were  of  uniform  size  and 
perfect  spheres,  and  arranged  in  the  most  compact  manner,  the  volume 
of  pore-space  would  be  about  26  per  cent  of  the  total  volume.  Owing 
to  irregularities  in  form  and  arrangement  the  porous  space  is  usually 
greater  than  this.  In  sand  of  a  fairly  uniform  size  it  is  commonly  from 
35  to  40  per  cent.  Mixed  sand  and  gravel  will  have  a  smaller  per- 
centage of  voids,  the  decrease  depending  on  the  variation  in  size  of 
particles;  but  it  will  seldom  be  less  than  25  per  cent.  Rocks  will  vary 
in  porosity  froxn  a  very  small  fraction  of  I  per  cent  in  the  case  of  some 
granites  to  25  or  even  30  per  cent  for  some  loose-textured  sandstones. 

The  amount  of  moisture  which  a  soil  or  rock  will  absorb  is,  how- 
ever, not  of  so  much  importance  to  the  water-w'orks  engineer  as  is  the 
carrying  capacity  and  the  amount  which  can  readily  be  drawn  from 
such  material  when  previously  saturated.  In  fine  soils  the  movement 
of  the  water  is  so  slow  and  such  a  large  part  of  the  water  is  retained 
by  capillary  action  that  such  soils  are  of  little  value  as  carriers  of 
water;  and  to  obtain  economically  the  large  quantities  required  for 
public  supplies  it  is  necessary  that  the  water-bearing  material  be  of  a 
very  open,  porous  .character.  Adequate  supplies  are  rarely  obtained 
from  anything,  but  sand  and  gravel  deposits,  or  from  very  porous  rock. 

The  absorptive  capacities  of  various  rock  formations  and  of  soils  are 
given  in  Table  No.  19. 

82.  Formations  Favorable  for  the  Transmission  of  Ground-water.— 
Rock  formations  are  divided  into  two  general  classes,  the  igneous  and 


92 


GR  O  UND-  WA  TER. 
TABLE   NO.    19. 

POROSITY   OF   VARIOUS    FORMATIONS,    IN    PER   CENT,    BY   VOLUME. 


Formation. 

Locality. 

Porosity 
Percentage.* 

Authority. 

O.O2  tO  1.5 

2.7 

9-8 
11.7 
10.8 
13-9 
23-7 
4-4 
13-2 

12  tO  26 

0.019  to  0.62 

13.17 

11.66 
1.04 
0.58 
28.26 
20.19 
7.12 
19.06 
14  to  17 
14  to  44 
35  to  45 
25  to  30 
41.8 
37  to  45 

Merrillf 

Gilbert* 
Buckley§ 

HumberJI 

Whitnevlf 
ii 

Joliet,  111. 
Bedford,  Ind. 
Winona,  Minn. 
Marquette,  Mich. 
Fort  Snelling,  Minn. 
Jordan,  Minn. 
Medina,  N.  Y. 
Berea,  O. 
Colorado 
Wisconsin 
Bridgeport,  Wis. 
Fountain  City,  Wis. 
Duck  Creek,  Wis. 
Sturgeon  Bay,  Wis. 
Dunnville,  Wis. 
Lake  Superior,  Wis. 
Ablemans,  Wis. 
Argyle,  Wis. 
England 

« 

ci 

«i 

14 

Dakota  sandstone  

Granite  

Lower  magnesian  limestone.. 

«                                       44 

44                                       « 

Chalk  

South  Carolina 
Maryland 

Truck  land  

*  The  figures  from  Merrill  were  obtained  by  multiplying  his  "  ratio  of  absorp- 
tion "  by  the  specific  gravity  of  the  stone. 

f  Stones  for  Building  and  Decoration.     New  York,  1897. 
\  Report  U.  S.  Geolog.  Survey,  1895-96,  p.  584. 
§  Bulletin  No.  4,  Wisconsin  Survey,  1898. 
|  Water-supply  of  Cities  and  Towns,  p.  47. 
IT  Bulletin  No.  4,  Weather  Bureau,  1892,  p.  25. 

the  sedimentary  rocks.  To  the  former  class  belong  the  granites, 
syenites,  and  gneisses;  these  rocks  are  usually  very  dense  and 
impervious  and  therefore  poor  water-carriers,  but  occasionally  they 
may  furnish  considerable  water  by  virtue  of  their  decomposed  and 
fissured  condition  near  the  surface.  Of  the  sedimentary  rocks,  those 
composed  of  very  fine-grained  material,  such  as  the  clays,  shales,  and 
other  argillaceous  deposits,  are  relatively  impervious.  Limestones  and 
dolomites  contain  little  water  as  a  rule,  but  if  fissured  they  may  be  the 
source  of  considerable  supplies.  The  most  favorable  formations,  by 
far,  for  furnishing  large  quantities  of  water,  are  the  various  sandstones, 
conglomerates,  and  gravel  deposits.  Sandstones  are  found  which  vary 
in  texture  from  a  very  compact  rock  having  a  very  small  degree  of 


OCCURRENCE  OF   WATER-BEARING  FORMATIONS.  93 

porosity  to  a  material  almost  as  porous  as  sand.  Uncemented  sands 
and  gravels  are  of  course  the  most  favorable  as  regards  porosity,  but 
they  are  apt  to  be  rather  limited  in  extent. 

83.  Occurrence  of  Water-bearing  Formations. — In  studying  the 
various  water-bearing  formations  from  the  engineer's  standpoint,  it  will 
be  convenient  to  divide  them  roughly  into  three  classes,  depending 
upon  their  extent  and  outline. 

1 I )  Broad,  extensive  formations  of  porous  material,  usually  of  con- 
siderable thickness  and  of  a  fairly  uniform  character  over  large  areas. 
In   the   case   of    formations    of    this   class   comparatively  few   widely 
scattered  borings  will  often  serve  to  give  a  reliable  knowledge  of  the 
strata,  and  wells  may  be  sunk  many  miles  apart  with  confidence  as  to 
the  result.     Most  of  the  deep  and  artesian  water  of  the  United  States 
is  obtained  from  such  formations,  some  of  which  underlie  great  areas  of 
country.     In   England  an  example  of  such  a  formation  is  the  immense 
deposit    of    chalk    which   underlies   a   large    part    of   the  country  and 
furnishes  much  water  for  public  supplies.     The  Tertiary  deposit  of  sand 
and    gravel    underlying    the    marl  throughout   a  large  portion   of   the 
Western  plains  is  supposed  to  have  once  been  the  bed  of  an  inland  sea. 
The  so-called  underflow,  or  ground-water  of  the  plains,  lies  chiefly  in 
this  formation,  and  wells  sunk  to  this  stratum  at  any  point  are  unfailing, 
These  deposits   are   estimated  at    from   17  to   120  feet  thick.     Other 
examples    of   extensive   water-bearing   formations   are   given    in  Arts. 
101-103. 

(2)  Deposits  of  porous  material  in  old  lake-  and  river-beds  often 
furnish  very  good   collecting-areas  for  ground-water,  and  many  of  the 


FIG.  18.  —  IDEAL  SECTION  OF  SAN  JOAQUIN  VALLEY,  CALIFORNIA. 

shallower  ground-water  supplies  are  from  such  sources.  These  deposits 
are  usually  covered  by  other  and  less  pervious  strata,  and  indeed  often 
consist  of  a  series  of  strata  alternately  of  a  pervious  and  nonpervious 
nature.  This  is  particularly  true  of  the  lacustrine  deposits  in  the  basins 
of  the  Western  mountain  region.  Fig.  18  is  an  ideal  section  through 
such  a  basin  in  California  and  shows  many  alternate  layers  of  clay  and 
gravel.* 

*  Report  on  Irrigation,  Part  I.  p.  321.     (U.  S.  Pub.  Document.) 


94  GROUND-  WA  TER. 

Old  river-channels  filled  with  debris  of  a  porous  character  give  rise 
to  veritable  ground-water  streams.  These  may  be  located  some  dis- 
tance from  the  modern  streams,  or  may  at  places  coincide  with  or 
underlie  them,  forming  porous,  gravelly  beds. 

Examples  of  such  ground-water  streams  are  very  numerous. 
Leipsic,  Germany,  is  supplied  from  such  a  stream  about  2  miles  in 
width,  40  feet  thick,  and  having  a  fall  of  about  6  feet  per  mile.  The 
covering  stratum  is  6  feet  thick,  and  the  velocity  of  flow  is  estimated 
at  about  8  feet  per  day.*  Pueblo,  Colorado,  is  supplied  with  water 
from  a  gravel-bed  66,000  square  feet  in  cross-section  with  an  average 
depth  of  14  feet  and  a  length  of  25  miles.  This  deposit  fills  the  former 
bed  of  a  stream  which  now  flows  partly  through  and  partly  over  the 
surface  of  the  gravel. t  Many  of  the  Western  streams  where  they 
emerge  from  the  mountains  are  of  a  similar  character. 

(3)  Deposits  of  sand  and  gravel  in  the  drift  are  often  of  consider- 
able extent,  and  furnish  many  ground-water  supplies,  but  such  deposits 
are  apt  to  be  very  irregular  in  character  and  uncertain  in  extent. 
They  occur  as  accumulations  in  former  stream-beds  and  also  in  the 
form  of  thin,  irregular  strata,  sometimes  of  considerable  extent,  lying 
for  the  most  part  in  valleys  and  covered  with  more  or  less  clay. 

Still  another  formation  of  much  value  in  certain  localities  is  the 
dune-sand,  such  as  occurs  so  extensively  in  Holland  and  from  which 
many  of  the  water-supplies  of  that  country  are  drawn. 

In  seeking  ground-water  supplies  a  study  of  the  geology  of  the 
region  is  essential  to  intelligent  action.  Such  a  study  will  generally 
enable  a  decision  to  be  made  as  to  whether  or  not  a  supply  is  likely  to 
be  obtained  from  the  deeper  strata,  and  will  give  much  information  as 
to  the  nature  of  the  glacial  or  other  surface  deposits.  The  location  of 
extensive  deposits  in  valleys  is  often  shown  by  wells  in  the  vicinity, 
but  at  other  times  they  can  be  located  only  by  a  careful  study  of  surface 
indications  and  by  borings. 

FLOW  OF  GROUND-WATER. 

84.  Methods  of  Determining  the  Flow  of  Ground-water — When  a 
particular  ground-water  source  is  to  be  investigated  for  a  water-supply, 
the  same  question  must  be  answered  as  in  the  case  of  a  surface  supply, 
namely,  what  is  the  quantity  of  water  available  from  day  to  day  from 
the  given  source  ?  In  the  case  of  a  surface  stream  the  rate  of  discharge 

*  Jour.  f.  Gasbel.  u.   Wasscrvers.,  1881,  p.  686. 
f  Eng.  News,  1891,  xxv.  p.  53. 


FORMULA   FOR  FLOW.  95 

is  determined  by  multiplying  the  observed  velocity  by  the  cross-section 
of  the  stream,  and  such  observations  carried  on  for  a  considerable 
length  of  time  will  give  the  necessary  information,  In  the  case  of  a 
ground-water  supply  similar  determinations  would  be  desirable,  but  they 
are  much  more  difficult  to  make. 

The  best  method  of  estimating  capacity  is  by  means  of  actual 
pumping  tests  carried  on  for  a  sufficient  length  of  time  to  bring  about 
an  approximate  state  of  equilibrium  between  the  supply  and  the 
demand  as  determined  by  the  level  of  the  ground-water.  It  will  rarely 
be  practicable  to  continue  such  tests  until  perfect  equilibrium  is  reached, 
for  in  many  cases  several  years  of  operation  would  be  required  to  deter- 
mine the  ultimate  capacity  of  a  source.  Pumping  tests  of  short  dura- 
tion are  apt  to  be  very  deceptive,  as  the  ground-water  may  exist  in  the 
form  of  a  large  basin  or  reservoir  with  very  little  movement,  corre- 
sponding to  a  surface  pond  with  small  watershed,  and  brief  tests  would 
give  but  little  more  information  than  similar  tests  on  a  pond. 

Where  it  can  be  done  it  is  very  desirable  to  get  an  approximate 
idea  of  the  amount  of  water  actually  flowing  per  unit  of  time  through 
the  area  in  question.  This  may  be  done  by  estimating  the  velocity  of 
flow,  the  cross-section  of  the  porous  stratum,  and  the  percentage  of 
porous  space ;  or  an  approximate  estimate  can  sometimes  be  made  by 
estimating  the  probable  percolation  on  the  tributary  area. 

85.  Formula  for  Estimating  Velocity  of  Flow. — The  velocity  of  flow 
of  a  ground-water  stream  is  a  function  of  the  hydraulic  gradient,  or 
slope,  on  the  one  hand,  and  the  resistance  to  flow  offered  by  the 
particles  of  soil  on  the  other. 

The  slope  can  readily  be  determined  by  borings  sunk  to  ground- 
water  level,  care  being  taken  to  measure  it  in  the  direction  of  greatest 
declivity.  In  case  the  porous  stratum  is  overlaid  by  a  more  or  less 
impervious  one  the  water  in  the  lower  stratum  may  flow  under  a  pres- 
sure greater  than  atmospheric.  The  slope  or  hydraulic  gradient  is  then 
found  by  determining  the  height  to  which  the  water  will  rise  in  tubes 
sunk  to  the  porous  stratum,  care  being  taken  to  prevent  the  escape  of 
water  between  the  tube  and  the  upper  strata.  Samples  of  the  material 
can  also  be  obtained  at  the  same  time  and  examined  as  to  size  and 
porosity.  The  latter  element  is  influenced  not  only  by  the  variation  in 
size  of  grain,  but  also  by  the  degree  of  compactness  of  the  material  in 
its  natural  bed ;  it  can  therefore  be  only  approximately  determined  from 
loose  samples.  The  size  can  readily  be  determined  by  means  of 
sieves.* 

*  For  further  details  relating  to  sand  analysis,  see  Art.  511. 


96  GRO  UND-  WA  TER. 

These  elements  having  been  determined,  it  remains  to  express  the 
relation  between  them  and  the  velocity  of  flow. 

Experiments  by  Darcy,  Hagen,  Hazen,  and  others  show  that  the  rate 
at  which  water  at  a  given  temperature  will  flow  through  any  particular 
sand  or  fine  gravel  follows  closely  the  law  of  flow  through  capillary 

tubes,  that   is,  the  velocity  is  approximately  proportional  to  —  ,  where 

h  is  the   head,  and  /  is  the  distance  through  which   the  water  flows. 
(In  the  case  of  a  stream  flowing  through  such  material  down  a  uniform 

slope,    —  would  be  the  sine  of  the  slope  angle.) 

For  different  grades  of  material  the  velocity  depends  primarily  upon 
the  size  of  the  pore  spaces  contained  therein.  This  is  a  function  of  the 
size  of  the  grains  of  the  material  and  the  degree  of  compactness  with 
which  they  are  arranged.  For  a  sand  of  uniform  size  and  of  a  given 
degree  of  compactness  it  is  found  that  the  velocity  of  flow  is  closely 
proportional  to  the  square  of  the  diameter  of  the  sand  grain  ;  and,  ex- 
pressing the  degree  of  compactness  in  terms  of  the  percentage  of  pore 
space,  it  is  found  that  for  materials  of  the  same  size  the  velocity  of  flow 
through  the  pores  is  roughly  proportional  to  the  square  of  the  porosity 
ratio.  The  volume  of  flow,  which  is  equal  to  the  velocity  multiplied  by 
the  area  of  net  section,  is  thus  proportional  to  the  cube  of  the  porosity.* 

Natural  sands  and  gravels  vary  greatly  in  character,  consisting  of 
material  of  many  different  sizes  and  of  different  degrees  of  porosity  as  a 
result  of  differences  in  compactness  and  of  differences  in  the  proportions 
of  large  and  small  grains.  These  conditions  render  it  difficult  to  apply 
mathematical  formulas  or  to  reduce  experimental  results  to  a  work- 
ing basis.  The  results  obtained  by  Hazen  from  experiments  on 
filter  sands  f  are  probably  the  most  widely  known  in  this  field.  The 
formula  derived  by  him  as  applicable  to  sands  of  from  o.i  to  3.0  mm. 
effective  size  is 

(FahQ 


60° 


where  v  =  velocity  in  meters  daily  of  a  solid  column  of  the  same  cross- 

section  as  that  of  the  sand  ; 
c  =  a  constant  =  400  to  1000; 
d  =  effective  size  of  sand  grains  in  millimeters  ; 
h  =  head  of  water  causing  motion  ; 

*  Slichter,  W.  S.,  Paper  No.  67,  U.  S.  G.  S.,  1902;  also  I9th  annual  report  U.  S.  G. 
S.,  Pt.  ii.  1899,  p.  295. 

t  Report  Mass.  Board  of  Health,  1892,  p.  553. 


FORMULA   FOR    FLOW.  97 

/  =  thickness  of  sand  layer  (-  =  slope  of  ground-water  surface j  ; 
/  =  temperature  in  degrees  Fahrenheit. 

The  "  effective  size  "  is  a  very  important  element  in  the  formula.  In 
the  natural  material,  consisting  of  coarse  and  fine  particles,  it  is  obvious 
that  the  size  of  the  pore  space  is  chiefly  determined  by  the  size  of  the 
finer  "particles,  and  that  a  small  per  cent  of  fine  particles  will  cause  an 
otherwise  coarse  sand  to  become  essentially  a  fine  sand  so  far  as  the 
transmission  of  water  is  concerned.  As  the  result  of  experiments  it 
was  concluded  by  Hazen  that  the  maximum  size  of  the  finest  10  per 
cent  of  the  material  represented  fairly  well  the  "effective  size"  of  the 
sand  as  a  whole;  that  is,  the  "effective  size"  is  the  size  of  grain,  such 
that  10  per  cent  of  the  particles  are  smaller  and  90  per  cent  are  larger 
than  this  size.  To  express  variations  in  proportions  of  large  and  small 
particles  a  "uniformity  coefficient"  was  devised.  This  is  the  ratio  of 
the  size  of  grain  such  that  60  per  cent  of  the  sand  is  finer  than  this 
size,  to  the  u effective  size"  above  described.  Ordinary  sands  will  have 
uniformity  coefficients  of  from  1.5  to  2.5.  The  analysis  of  a  sand 
may  be  made  by  sieves  as  more  fully  described  in  Art.  511. 

The  value  of  the  constant  c  in  Eq.  ( i )  varies  with  the  compactness  and 
uniformity  of  the  sand.  For  new  clean  sand  of  a  fairly  uniform  charac- 
ter, it  varies  from  700  to  1000;  for  old  compacted  sand  it  may  be  as 
low  as  400. 

Assuming  a  porosity  of  40  per  cent,  the  actual  average  velocity  of 
flow  through  the  pore  spaces  will  be  2.5  times  that  given  in  Eq.  (i). 
Neglecting  temperature  corrections,  as  being,  in  any  case,  small  for 
ground-waters,  we  derive  the  following  value  of  velocity  in  foot  units, 

v  =  8.2  cd2  s  =  k  s (2) 

where  v  =  actual  average  velocity  through  the  pores  of  the  sand  in 

feet  per  day ; 

d  =  effective  size  of  sand ; 

s  =  slope  of  free  ground-water  surface,  or  the  hydraulic  gradient ; 
k  =  8.2  cd*  =  velocity  for  a  slope  of  unity. 

A  sand  of  an  effective  size  of  o.io  mm.  would  be  called  a  very  fine 
sand,  one  of  0.3  a  medium  sand,  and  one  of  0.5  a  very  coarse  sand, 
although  much  depends  on  the  uniformity. 

In  estimating  the  value  of  k  it  is  to  be  noted  that  the  coefficient  c 
varies  considerably  with  the  porosity.  Professor  Slichter,  in  the  papers 


98 


GRO  UND-  WA  TER. 


already  referred  to,  calculates  the  following  values  of  relative  velocities  of 
flow  in  material  of  the  same  size  but  of  varying  porosities  due  to  differ- 
ent degrees  of  compactness  : 


Porosity  per  cent 

2C 

7Q 

-if 

4O 

Relative  velocity 

34. 

e-2 

74 

IOO 

Taking  a  value  of  c  equal  to  1000  for  a  porosity  of  40  per  cent  and  re- 
ducing it  in  accordance  with  the  above  values  for  lower  porosities,  we 
derive  the  approximate  values  of  k  given  in  Table  No.  20. 

TABLE    NO.  20. 

VALUES  OF   k  IN   EQ.    (2)   FOR  VARIOUS   VALUES   OF  d  AND  FOR  VARIOUS  POROSITIES. 


(d)    Effective  Size  of  Sand  in  Millimeters. 

Porosity, 

Porosity, 

Per  cent. 

Per  cent. 

.  I  O 

.  20 

•  30 

.  40 

.50 

.80 

I  .  00 

2.  OO 

3  •  oo 

25 

28 

112 

251 

446 

6Q7 

1,780 

2,790 

11,150 

25,100 

25 

3° 

43 

171 

384 

681 

i,  066 

2,730 

4,260 

17,05° 

38,400 

3° 

35 

61 

243 

546 

970 

i»5i7 

3,880 

6,070 

24,270 

54,600 

35 

40 

82 

328 

738 

i,312 

2,050 

5,248 

8,200 

32,800 

73,800 

40 

For  sands  of  low  uniformity,  and  mixtures  of  sand  and  gravel,  the 
velocity  will  still  depend  on  the  size  of  the  finer  particles  ;  and  if  the 
larger  stones  are  neglected  in  the  estimation  of  the  effective  size,  the 
above  formula  may  still  be  used  as  an  approximation. 

Lembke  suggests  values  of  k  as  follows,  based  on  experiments  of 
Darcy,  Krober,  and  others  :* 

Material.  k  in  Feet  per  Day. 

Sand  and  gravel 9,4°° 

Coarse  sand 2,800 

Medium  sand 7^° 

Fine  sand 15° 

In  Professor  Slichter's  investigations  the  effective  size  was  deter- 
mined by  measuring  the  flow  of  air  through  a  sample  of  the  material  by 
means  of  King's  aspirator. f  This  method  of  determining  the  effective 
size  probably  gives  more  accurate  results  than  any  other  method  yet 
devised,  but  it  is  not  in  general  use.  Comparing  the  work  of  Hazen 
and  Slichter  it  would  seem  that  the  size  reported  as  the  effective  size  of 
a  given  sand  is  somewhat  smaller  in  the  former  case  than  in  the  latter. 

*  Revue  Univ.  des  Mines,   1888,  I.  p.   155. 

t  Fifteenth  Ann.  Kept.,  Agr.  Exp.  Sta.,  University  of  Wisconsin,  1898,  p.  123. 


DETERMINING    VELOCITY  OF  FLOW. 


99 


86.  Coefficients  for  Coarse  Gravels.  —  For  gravels  larger  than  3  mm. 
and  containing  little  or  no  fine  material,  experiments  indicate  that  the 
velocity  increases  at  a  less  rate  than  the  square  of  the  diameter,  and 
also  less  rapidly  than  the  slope.  Results  of  such  experiments  on 
screened  gravel  are  given  in  Table  No.  21  as  indicating  in  a  general 
way  the  variation  in  velocity  in  coarse  gravel  deposits. 

TABLE   NO.    21. 

VELOCITIES    OF    FLOW    OF    WATER   IN    FEET    PER   DAY    IN    SCREENED    GRAVEL,    ASSUMING 

40   PER   CENT   POROSITY.       BASED   ON    EXPERIMENTS    OF    THE    MASSACHUSETTS 

STATE    BOARD    OF    HEALTH.* 


Effective  Size  of  Millimeters. 

Slope,  s. 

3 

5 

8 

10 

is 

20 

25 

30 

35 

40 

.0005 

28 

82 

164 

246 

410 

656 

902 

1,230 

1,640 

2,050 

.001 

57 

172 

335 

475 

820 

1,210 

1,  680 

2,250 

3,03° 

3,69o 

.002 

US 

328 

639 

902 

i,55° 

2,250 

3.030 

3,930 

4,830 

5,820 

.004 

221 

631 

1,230 

1,700 

2,870 

3,93° 

5,000 

6,060 

7,130 

8,200 

.006 

336 

918 

1,690 

2,250 

3,69° 

5,080 

6,39° 

7,620 

8,93° 

10,100 

.008 

443 

1,160 

2,060 

2,780 

4,340 

5)90° 

7,380 

8>93° 

10,400 

1  1,  800 

.010 

549 

1,410 

2,460 

3,15° 

5,000 

6,800 

8,440 

10,000 

11,500 

87.  Direct  Method  of  Determining  Velocity  of  Flow. —  The  rate  of 
flow  of  ground-water  may  be  directly  determined  by  tracing  the  move- 
ment of  a  soluble  salt  introduced  into  the  ground-water  stream.  The 
first  to  employ  this  method  for  this  purpose  was  probably  Thiem  of 
Germany,  who  has  studied  the  flow  of  ground-water  at  several  places 
with  good  results.f  His  method  is  as  follows  : 

Three  or  four  borings  are  sunk  to  ground-water  in  a  line  in  the 
direction  of  flow.  A  large  dose  of  salt  is  then  put  into  the  upper  hole, 
and  at  frequent  intervals  analyses  are  made  of  water  drawn  from  each 
hole  below  until  the  salt  content  has  reached  its  maximum  in  each  case, 
and  the  rate  of  movement  is  inferred  from  these  results. 

At  Stralsund,  velocities  of  12.9,  12,6,  and  12.0  feet  per  day  were 
found  in  this  way,  with  a  slope  of  2  per  cent ;  and  a  velocity  of  13.1 
feet  at  another  place.  The  former  values  would  correspond  to  a  value 
of  k  equal  to  about  625,  or  to  that  for  a  medium  sand. 

A  much  more  expeditious  method  is  that  developed  by  Professor 
Slichter.J  In  this  method  the  movement  of  salt  is  determined  by 
electrical  means  in  a  very  convenient  way.  The  arrangement  of  appar- 

*  Report,  1892,  p.  555. 

t  Jour.  /.    Gasbel.  u.    Wasservers.,  1888,  p.   18. 

\   W.  S.  Paper  No.  67,  U.  S.  G.  S.,  1902,  p.  47.     Eng.  News,  1902,  XLVII.  p.  151. 


IOO 


GROUND-  WA  TER. 


atus  is  shown  in  Fig.  i8a.  Two  small  drive  wells  are  sunk  three  or 
four  feet  apart  and  in  the  line  of  flow,  if  this  is  known.  Both  wells  are 
provided  with  brass  strainers,  through  which  the  ground-water  may 
enter  readily.  An  electric  battery  with  ammeter  is  connected  to 
the  wells  as  shown.  One  terminal  is  connected  to  the  casing 
of  the  upper  well  and  also  to  an  electrode  of  brass  inserted  in 
the  lower  well  and  insulated  from  the  casing  of  this  well.  The  other 
terminal  is  connected  to  the  casing  of  the  lower  well.  An  electrolyte 
is  introduced  in  a  single  dose  into  the  upper  well.  As  this  passes 
towards  the  lower  well  with  the  ground-water  the  amount  of  current 
passing  from  casing  to  casing  will  gradually  increase.  When  the 
electrolyte  reaches  the  lower  well  and  enters  it,  a  short  circuit  will  be 


FIG.  i8a. — .  ARRANGEMENT  OF  WELLS  FOR  DETERMINING  VELOCITY  OF  FLOW. 
created  between  the  interior  electrode  and  the  well  casing  and  there 
will  be  a  sudden  increase  in  current.*  Fig.  i8b  illustrates  a  typical 
curve  thus  obtained.  The  point  "A"  represents  the  instant  when  the 
electrolyte  was  introduced  into  the  upper  well ;  the  point  of  inflection 
of  the  steep  part  of  the  curve  at  "B"  represents  the  time  when  the 
electrolyte  reached  the  lower  well.  Except  for  the  effect  of  diffusion 
the  steep  portion  would  be  a  vertical  line.  The  portion  of  the  curve  to 
the  left  of  the  steep  part  shows  a  slow  increase  in  current  passing  from 
casing  to  casing.  This  information  assists  in  estimating  the  regularity 
of  flow  and  is  especially  valuable  when  the  electrolyte  entirely  misses 
the  lower  well  through  an  erroneous  estimate  of  the  direction  of  flow. 
Where  this  occurs  additional  wells  may  be  sunk  until  one  is  obtained  in 
the  line  of  flow. 

*  From  W.  S,  Paper  No.  67,  p.  49. 


QUANTITY  FLOWING. 


IOI 


The  most  convenient  electrolyte  seems  to  be  ammonium  chloride. 
Where  the  velocity  is  very  high  caustic  soda  has  been  added  in 
order  to  cause  greater  diffusion,  and  thus  to  make  it  more  certain 
that  the  direct  effect  will  be  felt  in  the  lower  well  if  somewhat  out 
of  line. 

Measurements  of  velocities  of  the  underflow  of  several  of  the  western 
streams  have  been  made  by  Professor  Slichter.  Velocities  of  from  5  to 
10  feet  per  day  are  common,  while  velocities  as  high  as  50  feet  per  day 
have  been  observed  in  a  coarse  deposit  with  a  slope  of  20  feet  per 
mile.*  Average  velocities  of  about  4  feet  per  day  have  been  measured 
on  Long  Island. 

88.  Quantity  Flowing. — The  velocity  of  flow  having  been  deter- 
mined, also  the  porosity  of  the  material  and  the  cross-section  of  the 


e 

-v, 

( 

s, 

I 

\ 

\ 

\ 

516 

\ 

' 

/: 

s^ 

5 

J; 

x 

n     .1 

> 

; 

^s 

^ 

«    no 

x 

•**. 

~^, 

^ 

x" 

x: 

^ 

- 

~ 

•—  «- 

-—  . 

= 

= 

= 

T 

U— 

^ 

.00 

2 
A 

.  1 
* 

A 

J 

I 

. 

J 

( 

> 

r 

8 

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3 

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) 

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0 

1 

1 
7 

1 
'/A 

a 

/<£ 

X 

./u 

c 

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i 

b 

3 

( 

r 

( 

3 

FIG.  i8b.  —  CURVE  SHOWING  TRANSMISSION  OF  ELECTROLYTE. 
(From  W.  S.  Paper  No.  67.) 

porous  stratum  at  right  angles  to  the  direction  of  flow,  the  total  rate  of 
flow  will  be  the  product  of  these  three  factors,  or 

Q  =  velocity  X  area  of  cross-section  X  porosity  =  vAp  =  ksAp,     (3) 

in  which  the  units  are  the  foot  and  day.  Irregularities  in  cross-section, 
slope,  and  material  will  of  course  render  the  result  more  or  less  uncer- 
tain, but  estimates  made  in  this  way  will  nevertheless  be  of  very  con- 
siderable value  in  examinations  of  ground -water  sources,  and  will  tend 
to  modify  the  very  exaggerated  notions  which  frequently  prevail  con- 
cerning their  capacity. 

*  The  river  Mohave,  Jour.  West.  Soc.  Eng'rs.,  1904,  ix.  p.  635. 


102 


GROUND-  WA  TER.' 


In  Table  No.  22  are  given  the  rates  of  flow  in  sands  of  different 
degrees  of  fineness  and  porosity,  and  for  a  slope  of  I  per  cent.  For 
other  slopes  multiply  by  the  slope  expressed  in  per  cent.  In  this  table 
the  rates  of  flow  for  porosities  below  40  per  cent  have  been  reduced  in 
accordance  with  the  coefficients  of  Art.  85. 

An  inspection  of  this  table  will  show  clearly  that  it  requires  very 
extensive  areas  and  collecting-works  to  obtain  much  ground-water  from 
fine  material ;  and  even  with  coarse  material,  if  the  slopes  are  flat  (they 
are  frequently  only  one-tenth  of  I  per  cent),  a  relatively  large  cross- 
section  must  be  available. 

TABLE   NO.    22. 

RATES   OF  FLOW  OF  GROUND-WATER  FOR  A  ONE  PER  CENT   SLOPE   (s  =  .Ol)   IN  GALLONS 
PER   DAY  PER    SQUARE    FOOT   OF   CROSS-SECTION. 


Porosity, 

(d)  Effective  Size  of  Sand  in  Millimeters, 

Porosity, 

Per 

Per 

cent. 

cent. 

.10 

.20 

.30 

.40 

•  5° 

.80 

1.  00 

2.00 

3.00 

25 

0.51 

2.6 

4-7 

8 

13 

33 

52 

208 

470 

25 

3° 

0.90 

3-8 

8.6 

15 

24 

61 

96 

3»3 

862 

3° 

35 

1.6 

6.4 

14.4 

25 

39 

102 

160 

635 

1,43° 

35 

40 

2.4 

9.8 

22.  I 

39 

61 

157 

246 

980 

2,210 

40 

89.  Quantity  Available. — The  proportion  of  the  ground-water  that 
can  be  intercepted  depends  upon  the  character  of  the  collect  ing- works, 
a  question  which  will  be  discussed  in  Chapter  XIV.     The  useful  capa- 
city of  such  a  supply  —  the  quantity  which  it  can  deliver  daily  through- 
out the  year  —  depends  upon  the  minimum  rather  than  the  average  flow, 
and  in  determining  the  flow  a  dry  period  should  be  selected  if  possible. 
The  natural  storage  furnished  by  the  ground  not  only  renders  the  flow 
ordinarily  quite  uniform,  but  enables  the  draught  to  more  or  less  exceed 
the  minimum  flow;  and  if  the  character  of  the  works  is  such  that  the 
ground-water  level  can   be  considerably  lowered,  this  natural  storage 
can    be  made  to  increase  very  materially    the   daily  capacity  of   the 
source.     In   estimating   the    capacity  of  a    source    by  estimating   the 
percolation,  this  element  of   ground-storage  must  be  taken  into  con- 
sideration. 

SPRINGS. 

90.  Formation  of   Springs. — Springs    are   formed   where,    for   any 
reason,  the  ground-water  is  caused  to  overflow  upon  the  surface.     The 


FORMATION  OF  SPRINGS.  103 

conditions  causing  their  formation  are  varied  and  should  be  carefully 
studied  in  connection  with  the  design  of  collecting-works,  as  upon 
them  depend  largely  such  questions  as  the  constancy  of  flow,  the 
possibility  of  increasing  the  yield  by  suitable  works,  and  the  probable 
success  of  a  search  for  additional  springs.  According  to  differences  in 
these  conditions  springs  may  be  divided  into  three  general  classes,  each 
of  which  will  be  discussed  separately. 

91.  First  Class. — The  most  important  class  of  springs  is  that  in 
which  the  water,  in  its  lateral  movement,  is  brought  to  the  surface  at 
the  outcrop  of  a  porous  stratum  where  it  is  underlain  by  a  relatively 
impervious  one  (Fig.  19).  The  porous  stratum  may  be  sand  or  gravel, 


FIG.  19. 

or  a  porous  rock;  while  the  impervious  layer  is  usually  clay,  or  rock 
of  an  argillaceous  character. 

If  the  porous  material  is  fairly  uniform,  the  springs  will  be  scattered 
all  along  the  outcrop  and  will  be  small  in  size,  the  larger  amounts  of 
water  appearing  in  the  valleys  or  re-entrant  angles  of  the  outcrop.  If 
the  porous  deposit  be  much  fissured,  especially  if  the  rock  itself  be 
fine-textured,  the  location  of  a  spring  is  largely  a  matter  of  chance, 
although  topography  controls  in  a  general  way. 

There  are  many  cases  of  large  springs  of  this  class,  the  supplies  for 
some  of  the  largest  cities  of  Europe  being  obtained  from  such  sources. 
The  city  of  Vienna  is  supplied  from  springs  60  miles  distant  that  occur 
at  the  outcrop  of  a  fractured  dolomitic  limestone  underlain  by  slate. 
The  largest  spring,  the  Kaiserbrunnen,  has  an  average  flow  of  about 
150  gallons  per  second,  varying  from  60  to  about  250.*  Munich 
receives  its  supply  from  galleries  constructed  in  fissured  slate,  which 
collect  the  ground-water  that  previously  appeared  in  part  as  springs  at 
the  surface  of  the  slate,  and  in  part  flowed  through  fissures  into  the 
river  below.  Baden-Baden  intercepts,  by  means  of  a  gallery  about 
2  miles  long,  several  springs  occurring  at  the  junction  of  granite  and 
overlying  sandstone.  The  flow  varies  from  4  to  1 8  gallons  per  second, 
averaging  about  8.t 

*  Lueger,  p.  410.  \Ibid.%  pp.  275,  400. 


1 04  GRO  UND-  WA  TER. 

In  the  United  States  many  supplies  of  considerable  amount  are 
obtained  from  similar  springs,  the  most  noteworthy  instance  being 
perhaps  that  of  Roanoke,  Va.  The  supply  there  is  from  a  spring 
issuing  from  the  limestone  and  having  a  flow  of  about  5,000,000 
gallons  per  day. 

92.  Second  Class. — Under  this  class  are  considered  those  springs 
where  the  water-bearing  stratum  is  covered  to  a  greater  or  less  extent 
by  an  impervious  one,  and  which  are  therefore  more  or  less  artesian  in 
character.  In  this  case  the  water  finds  its  way  to  the  surface  where 
the  overlying  impervious  material  is  wanting,  or  through  a  fault,  or  it 
breaks  through  at  places  where  it  is  not  sufficiently  strong  or  compact 
to  resist  the  upward  pressure.  Most  of  the  springs  which  occur  in  the 
drift  are  of  thig  character,  the  alternating  layers  of  sand  and  clay  so 
often  found  there  being  favorable  to  their  formation. 

In  Fig.  20  is  given  a  section  showing  the  formations  immediately 


FIG.  20. — SPRING  AT  AVON,  MASS. 

surrounding  a  spring  of  this  kind,  located  at  Avon,  Mass.*  Here  the 
water  is  carried  by  coarse  gravel  which  is  overlain  by  hardpan.  The 
location  of  the  spring  at  this  point  was  doubtless  due  to  some  local 
weakness.  The  outcrop  of  the  porous  stratum  lies  considerably  higher 
than  the  spring. 

In  some  cases  springs  of  this  character  are  fed  by  water  coming 
long  distances  through  extensive  formations  which  at  other  points  offer 
conditions  favorable  for  artesian  wells.  Of  such  character  are  the 
artesian  springs  at  the  eastern  outcrop  of  the  Dakota  sandstone 
(Art.  102).  Conditions  of  this  sort  also  give  rise  to  the  peculiar 
phenomenon  of  large  fresh-water  springs  which  boil  up  in  the  ocean 
several  miles  out  from  the  Florida  coast,  and  it  is  supposed  that  the 
great  springs  in  northern  Florida  are  from  a  similar  cause. 

93.    The  Third  Class  of  Springs  includes  those  in  which  the  porous 

*Jour.  New  Eng.  W.  W.  Assn.,  1896,  xi.  p.  160. 


YIELD    OF  SPRINGS.  1 05 

stratum  in  the  vicinity  of  the  spring  is  neither  overlain  nor  immediately 
underlain  by  an  impervious  one.  They  are  mere  overflows  of  the 
ground-water,  and  occur  whenever  the  carrying  capacity  of  the  porous 
material  is  insufficient  to  convey  the  entire  tributary  flow. 

In  a  region  where  the  soil  is  very  porous  to  a  considerable  depth, 
the  surface-flow  of  streams  will  commence  only  at  a  considerable  dis- 
tance from  the  head  of  the  valley,  the  point  of  beginning  being  a  spring 
of  larger  or  smaller  size  of  the  class  under  discussion.  If  the  formation 
is  quite  uniform,  the  springs  will  be  small  and  numerous,  and  the  source 
of  the  stream  will  move  up  and  down  the  valley  according  to  the 
weather,  the  point  of  beginning  being  determined  by  the  carrying 
capacity  of  the  ground.  If  the  formation  is  irregular,  the  springs  tend 
to  be  larger  in  size.  In  irregular  formations  it  also  often  happens  that 
after  having  flowed  on  the  surface  for  some  distance  the  water  will 
again  disappear,  only  to  reappear  farther  down  the  valley.  Such 
action  is  noticeable  in  almost  any  small  brook,  but  in  certain  parts  of 
the  country  it  occurs  on  a  very  large  scale.  Where  springs  are  thus 
formed  by  water  that  has  recently  flowed  on  the  surface  the  character 
of  the  water  is  likely  to  differ  greatly  from  ground-water  proper. 

94.  Yield  of  Springs. — The  yield  of  any  particular  spring  can  readily 
be  determined  by  weir  measurements,  and  if  these  are  carried  out 
through  a  period  of  drought  they  will  give  all  needed  information  re- 
garding the  supplying  capacity  of  the  existing  spring.  If,  however, 
but  a  short  series  of  gaugings  is  available,  it  will  be  necessary  to  make 
allowances  for  variations  in  rainfall;  and  a  knowledge  regarding  the 
area  of  percolation,  quality  of  soil,  and  possibilities  in  the  way  of 
ground-storage  will  be  of  assistance  in  drawing  conclusions.  The 
possibility  of  increasing  the  flow  should  also  receive  attention. 

Springs  of  the  first  class  will  vary  in  yield  with  the  variations  in 
ground-water  level,  but  will  not  wholly  cease  to  flow  if  the  water  is 
intercepted  by  suitable  constructions.  The  yield  of  a  series  of  springs 
of  this  class  would,  if  the  lower  stratum  be  impervious,  be  equal  to  the 
entire  percolation  on  the  tributary  area.  This  area  is  determined  by 
the  direction  of  the  slope  of  the  ground-water  surface,  and  does  not 
always  correspond  with  the  watershed  for  surface-water.  Thus  in  Fig. 
19  more  water  will  appear  at  A  than  at  B. 

Springs  of  the  second  class  are  apt  to  be  much  less  affected  by 
variations  in  rainfall  than  either  the  first  or  the  third  class.  Their  yield 
varies  with  the  variation  of  the  ground-water  level  in  the  area  of  perco- 
lation, and  if  this  is  many  miles  distant,  as  is  the  case  with  many  artesian 
wells  or  springs,  the  flow  may  be  practically  invariable.  In  most 


1  06  GRO  UND-  WA  TER. 

cases,  however,  the  deposits  are  local  in  extent  and  the  variation  is 
considerable. 

Where  a  spring  of  this  class  exists,  investigation  may  show  that  the 
ground-water  stream  from  which  it  is  fed  is  of  considerable  size  and 
that  the  water  of  the  spring  is  but  a  small  portion  of  the  entire  flow. 
In  such  a  case  the  yield  may  be  increased  by  simply  enlarging  the 
opening,  or  by  sinking  wells  and  pumping  therefrom,  as  in  the  case  of 
an  ordinary  ground-water  supply. 

Springs  of  the  third  class  are  liable  to  very  great  fluctuations,  the 
flow  often  ceasing  entirely.  Occasionally,  owing  to  the  concentration 
of  large  volumes  of  ground-water  into  a  small  area,  conditions  are 
favorable  for  large  and  steady  yields.  Springs  of  this  class  form  the 
source  of  the  Vanne,  from  which  Paris  draws  a  portion  of  its  supply. 
The  largest  of  these,  '  '  Le  Birne  de  Cerilly,  '  '  has  an  average  yield  of 
about  50  gallons  per  second,  with  a  minimum  of  18  gallons. 

ARTESIAN   WATER. 

95.  General  Conditions.  —  Whenever  a  water-bearing  stratum  dips 
below  a  relatively  impervious  one  the  former  becomes  in  a  sense  a 
closed  conduit,  and  if  the  flow  out  of  this  conduit  at  the  lower  end  be 
impeded  from  any  cause,  the  water  will  accumulate  and  exert  more  or 
less  pressure  against  the  impervious  cover.  The  amount  of  this 
pressure  will  depend  on  the  extent  to  which  the  flow  is  obstructed  and 
on  the  elevation  of  the  upper  end  of  .the  conduit,  that  is,  of  the  outcrop 
of  the  porous  stratum.  If  a  well  be  sunk  through  this  impervious 


B    ^--  — 


FIG.  21. 

stratum  at  any  point,  the  water  will  rise  in  it  in  accordance  with  the 
pressure;  and  if  the  surface  topography  and  pressure  are  favorable,  the 
water  may  rise  to  the  surface,  or  considerably  above,  in  which  case  the 
well  becomes  a  true  artesian,  or  flowing,  well. 

The  obstruction  to  flow  at  the  lower  end  of  the  porous  stratum  may 
be  due  to  various  causes,  chief  among  which  are  the  three  following: 

I.  The  stratum  may  be  turned  up  at  the  lower  end,  thus  forming 
a  synclinal,  or  a  curved  conduit,  as  in  Fig.  21.  In  this  case  water 
entering  at  A  could  escape  at  the  lower  lip  B,  but  at  intermediate 


ARTESIAN    WATER.  IO; 

points  would  exert  a  pressure  on  the  covering.  If  the  resistance  to 
flow  were  uniform,  and  no  water  could  escape  except  at  B,  the  decrease 
of  head  from  A  to  B  would  be  uniform,  or  in  other  words  the  hydraulic 
grade-line  would  be  a  straight  line  AB.  Water  would  rise  to  this  line 
in  a  tube  sunk  to  the  porous  stratum,  and  a  flowing  well  would  be 
possible  wherever  the  surface  lies  below  this  line. 

2.  The  inclined  stratum  may  be  subjected  at  its  lower  outcrop  to 
hydrostatic  pressure  from  the  waters  of  the  ocean,  as  actually  occurs 
along  a  large  part  of  the  Atlantic  and  Gulf  coasts  of  the  United  States. 
The  conditions  obtaining  in  that  region  are  roughly  shown  in  Fig.  22. 


FIG.  22. — ARTESIAN  CONDITIONS  NEAR  OCEAN. 

In  this  case  a  porous  stratum  outcropping  at  A  and  passing  into  the 
ocean  at  B  would  be  subjected  to  a  pressure  throughout  its  length,  vary- 
ing according  to  some  hydraulic  grade-line  AC.  Flowing  wells  are 
here  possible  at  all  points  where  the  surface  falls  below  this  line. 

3.  An  increased  resistance  to  flow  is  frequently  caused  near  B,  Fig. 
22,  by  increased  density  of  the  stratum  or  by  a  decrease  in  thickness. 
Such  increased  resistance  will  have  the  effect  to  increase  the  slope  of 
the  hydraulic  grade-line  at  the  point  of  greater  resistance,  and  give  it 
a  form  something  like  the  line  ADC,  thus  making  conditions  still  more 
favorable  for  flowing  wells.  Complete  stoppage  at  B  and  no  leakage 
would  give  a  horizontal  grade-line  through  A.  Leakage  through  the 
overlying  strata,  or  flow  through  many  wells  as  at  E,  will  reduce  the 
pressure  and  consequently  lower  the  grade-line  to  AEC.  The  local 
effect  of  wells  upon  each  other  is  more  fully  discussed  in  Chapter  XIV. 

96.  Use  of  the  Word  "  Artesian." — The  term  "artesian"  was 
formerly  applied  exclusively  to  flowing  wells  and  is  derived  from  the 
word  "  Artois,"  the  name  of  a  province  in  France  where  such  wells 
were  first  extensively  bored.  More  recently,  however,  the  term  has 
come  to  be  applied  in  a  broader  sense,  according  to  which  an  artesian 
well  may  be  defined  as  one  in  which  the  water  is  drawn  from  a  porous 
stratum  underlying  a  relatively  impervious  one  and  so  located  that  the 


1 08  GRO  UND-  WA  TER. 

contained  water,  drawn  from  a  distant  elevated  outcrop,  naturally 
exerts  more  or  less  pressure  upon  the  overlying  cover.  Water  will  rise 
in  such  wells,  but  whether  it  will  overflow  depends  much  on  local  con- 
ditions, such  as  elevation  of  surface,  and  nearness  of  other  wells. 
Many  wells  once  flowing  have  ceased  to  flow  owing  to  increased 
draught  by  others,  and  wells  but  a  few  hundred  feet  from  others  sunk 
to  the  same  stratum  will  exhibit  variations  in  this  respect;  but  it  is  still 
convenient  to  call  all  such  wells  artesian,  and  the  water  artesian  water. 

97.  The  Character  and  Inclination  of  the  Strata,  both  of  the  porous 
stratum  and  the  impervious  cover,  largely  determine  the  capacity  and 
usefulness  of  the  artesian  area.      The  important  water-bearing  forma- 
tions of  an   artesian   character  belong  to  the  sedimentary  rocks,  but 
small  areas  of  considerable  local  importance  are  met  with  in  the  drift 
formation.      The  water-bearing  stratum  is  most  often  a  porous  sand- 
stone, although  artesian  water  is  also  obtained  from  limestone  and  in 
many  places  from  extensive  strata  of  loose  uncemented  material. 

The  overlying  impervious  strata  usually  consist  of  clays  and  shales, 
these  being  practically  impervious  except  where  fissured.  Probably 
some  leakage  always  takes  place  through  such  strata ;  but  a  condition 
favorable  to  small  leakage  is  the  existence  of  an  elevated  country 
between  the  outcrop  and  the  area  where  wells  are  practicable.  In  such 
a  case  the  ordinary  ground-water  level  is  likely  to  be  above  the 
hydraulic  grade-line  of  the  artesian  basin,  and  the  leakage  would  then 
tend  to  be  into  rather  than  out  of  the  confined  stratum. 

To  be  of  most  value  the  inclination  of  the  beds  of  an  artesian  forma- 
tion should  not  be  great,  a  steeper  inclination  than  is  necessary  to 
furnish  a  good  covering  being  disadvantageous.  A  small  inclination 
furnishes  a  wide  percolation  area  at  the  outcrop,  and  at  the  same  time 
the  area  is  large  over  which  the  stratum  can  be  reached  by  wells  of 
practicable  depth.  Thick  strata  give  proportionately  large  percolation 
area  and  great  carrying  capacity. 

It  often  occurs  that  water  is  obtainable  from  two  or  more  parallel 
strata.  In  such  cases  the  lower  usually  furnishes  the  higher  head,  the 
outcrop  being  more  remote  and  at  a  higher  elevation. 

98.  Capacity. — Except    in    the    case    of  very    limited    areas,    the 
capacity  of  an  artesian  source  as  a  whole  is  a  question  of  little  impor- 
tance where  it  is  to  be  used  only  for  water-supply  purposes  in  towns 
widely  separated ;  for  the  total  amount  of  water  capable  of  being  drawn 
from  porous  rock  strata,  often  hundreds  of  feet  thick  and  having  an 
outcrop  of  hundreds  or  thousands  of  square  miles,  is  ordinarily  very 
great  as  compared  to  any  possible  demands  for  such  purposes.     The 


CAPACITY   OF  ARTESIAN  AREAS. 

problem  is  rather  one  concerning  the  number  and  arrangement  of  wells 
to  furnish  a  given  quantity,  a  question  which  is  discussed  in  Chapter 
XIV. 

In  localities  where  wells  are  extensively  used  for  irrigation  purposes 
the  total  capacity  of  the  source  becomes  a  serious  question,  as  is  already 
the  case  in  some  portions  of  the  West. 

The  total  possible  yield  of  an  artesian  source  may  be  limited  either 
by  the  rainfall  and  percolation  on  the  outcrop  or  by  the  carrying 
capacity  of  the  strata.  With  the  slight  slopes  and  broad  outcrops 
commonly  occurring,  the  carrying  capacity  will  probably  determine  the 
maximum  yield,  while  with  steep  slopes  and  small  outcrops  the  water 
may  be  drawn  out  faster  than  it  flows  in. 

The  velocity  of  flow  through  the  pores  of  rock  formations  is  neces- 
sarily extremely  slow  on  account  of  the  great  resistance  offered.  In 
many  cases,  no  doubt,  fissures  and  other  openings  of  a  large  size  rela- 
tive to  that  of  the  pores  of  the  stone  add  very  greatly  to  the  carrying 
capacity  of  a  rock  stratum.  In  a  sandstone  formation  such  are  not  so 
likely  to  be  of  great  influence  as  in  the  case  of  limestone,  where  indeed 
they  may  be  the  controlling  factors  in  determining  the  capacity. 

99.  Some  rough  calculations  relating  to  the  flow  through  thick  porous 
strata  may  be  of  value  in  suggesting  the  possible  limitations  in  the  carrying 
capacity  of  sandstones  and  of  strata  of  loose  material. 

The  Potsdam  sandstone  of  northern  Illinois  and  southern  Wisconsin  has 
a  thickness  estimated  at  from  700  to  1200  feet,  and  a  width  of  outcrop  in 
Wisconsin  of  40  to  60  miles,  or  about  250  times  its  thickness.  The  percola- 
tion, with  a  rainfall  of  about  35  inches  may  at  the  very  lowest  be  taken  at 
5  inches  per  year.  Assuming  a  porosity  of  25  per  cent,  this  would  fill  the 
rock  to  a  depth  of  20  inches  vertically,  or  a  horizontal  length  of  the  stratum 
of  20  X  250  =  5000  inches,  or  417  feet.  Now  the  rate  of  flow  depends  upon 
the  available  head  or  hydraulic  slope,  which  in  the  region  here  considered 
would  not,  even  with  the  use  of  deep-well  pumps,  exceed  3  or  4  feet  per 
mile.  Assuming  the  resistance  to  flow  to  be  equal  to  that  in  a  fine  sand  of 
o.i  mm.  size  (it  is  probably  much  greater),*  the  velocity  would  be,  according 
to  the  tables  on  p.  98,  equal  to  82  x  .34  X  3^^  ft.  per  day  =  8  feet  per 
year,  a  very  much  less  rate  than  that  of  the  percolation.  If  the  material  were 
a  coarse  sand  of  a  size  of  0.35  mm.,  the  carrying  capacity  would,  under  the 
assumed  conditions,  be  about  equal  to  the  rate  of  percolation. 

In  some  basins  the  possible  slopes  are  somewhat  greater  than  in  the 
example  given,  but  it  will  seldom  be  found  that  artesian  areas  are  likely  to  be 
limited  in  supplying  capacity  by  the  lack  of  percolation. 

The  actual  quantity  flowing  through  a  given  cross-section  may  be  roughly 
estimated  in  the  same  manner  as  for  any  other  ground-water  stream.  In  the 

*  Some  experiments  by  King  on  the  flow  of  water  through  Madison  sandstone 
indicate  a  resistance  to  flow  equal  to  that  in  a  sand  of  an  effective  size  of  about  .03 
to  .05  mm.  See  Nineteenth  Annual  Report  U.  S.  Geolog.  Survey,  p.  140, 


110  GRO  UND-  WA  TER. 

case  above  discussed  the  flow  would  be  from  Table  No.  22,  p.  102,  equal  to 

.51    x  — - —  =  0.039  gallons  per  day  per  square  foot  of  cross-section,  or  for  a 
52.8 

section  i  foot  in  width  and  800  feet  deep  it  would  be  about  32  gallons  per 
day.  The  quantity  flowing  per  mile  in  width  would  therefore  be  about 
170,000  gallons  per  day,  and  this  would  represent  the  maximum  delivering 
capacity  of  a  line  of  collecting-works  of  indefinite  length.  For  isolated 
groups  of  wells  the  flow  is  lateral  as  well  as  in  the  direction  of  the  general 
slope,  and  the  capacity  is  relatively  very  much  larger.  In  view,  however,  of 
the  great  distances  over  which  large  draughts  affect  the  pressure  in  this  area 
it  is  doubtful  if  the  flow  is  much  greater  than  the  above  figure. 

100.  Predictions  Concerning  Artesian  Wells. — The  question  of  the 
existence  of  water-bearing  strata  at  any  point,  their  character  and 
depth,  and  the  location  of  outcrops,  is  a  geological  one;  and  where  full 
information  on  this  point  has  not  been  gained  by  the  sinking  of  wells 
or  by  borings,  a  geologist  familiar  with  the  region  in  question  should 
be  consulted.  Much  money  has  often  been  wasted  in  fruitless  attempts 
to  obtain  water  in  areas  and  at  depths  where  none  could  be  expected, 
and  frequently  such  work  has  been  carried  on  contrary  to  the  advice 
of  experts. 

The  pressure  which  will  exist  in  a  well  is  a  question  of  hydraulics. 
With  a  knowledge  of  the  pressure  in  neighboring  wells,  and  of  the 
surface  topography  and  elevation  of  outcrops,  a  fairly  close  estimate  of 
pressure  may  be  made. 

The  questions  of  percolation,  freedom  of  flow,  and  capacity  cannot 
of  course  be  very  closely  determined,  but  a  careful  consideration  of  the 
principles  of  hydraulics,  which  govern  here  as  elsewhere,  will  at  least 
enable  one  to  avoid  the  absurd  estimates  which  are  sometimes  made 
and  which  lead  to  disastrous  results. 

In  the  construction  of  wells  it  is  important  to  preserve  samples  of 
the  borings,  as  it  is  largely  through  these  that  a  knowledge  of  the 
geology  of  the  region  is  acquired.  Chemical  analyses  of  the  water  are 
also  a  valuable  aid  in  identifying  strata. 

101.  Important  Artesian  Areas  in  the  United  States. — The  Atlantic  and 
Gulf  Coast  Region. — One  of  the  most  extensive  and  important  artesian-well 
areas  in  the  United  States  is  that  which  borders  the  Atlantic  Ocean  and  Gulf 
of  Mexico,  extending  from  Long  Island  on  the  north  to  Texas  on  the  south. 
Along  the  Atlantic  coast  it  will  average  perhaps  100  miles  in  width,  but  along 
the  Gulf  it  broadens  out,  extending  up  the  Mississippi  valley  as  far  as  the 
Ohio  River,  and  in  Texas  it  has  a  width  of  200  to  300  miles. 

The  several  strata  in  which  water  is  found  belong  to  the  Cretaceous  forma- 
tion. They  outcrop  along  the  foothills  of  the  higher  country  to  the  west  .and 
north,  dip  towards  the  ocean  at  a  considerable  slope  (20  to  40  feet  per  mile 
along  the  Atlantic  coast),  and  presumably  have  their  lower  outcrop  in  the 


IMPORTANT  ARTESIAN  AREAS  IN   THE    UNITED   STATES.    Ill 

deeper  ocean  many  miles  from  shore.  Their  connection  with  the  ocean  is 
indicated  by  the  occurrence  of  ocean  springs  as  already  noted  (Art.  92),  and 
by  the  effect  of  the  tides  upon  the  pressure  in  certain  wells,  it  being  stated 
that  at  Pensacola  the  water-level  in  wells  located  several  feet  above  sea-level 
varies  from  6  to  10  feet  as  a  result  of  tidal  influence.* 

Fig.  22,  p.  107,  is  a  section  showing  arrangement  of  strata  typical  of  this 
region.  The  conditions  here  are  evidently  very  favorable  for  artesian  wells, 
and  the  various  water-bearing  strata  furnish  an  exceedingly  valuable  source  of 
water-supply  for  the  cities  of  this  region  that  otherwise  could  procure  pure 
water  only  at  much  cost.  Among  the  cities  which  get  their  supply  from  this 
source  are  Savannah,  Charleston,  Jacksonville,  St.  Augustine,  Key  West, 
Memphis,  Galveston,  and  Fort  Worth,  besides  a  large  proportion  of  the  other 
towns  in  Florida,  Mississippi,  and  Texas.  Many  wells  have  also  been  sunk 
in  Long  Island,  New  Jersey,  Delaware,  Maryland,  and  in  the  city  of  Phila- 
delphia. 

102.  Artesian  Areas  in  the  West. — Another  very  important  artesian  area, 
noted  for  its  high  pressures  and  the  great  number  of  wells,  is  that  of  the 
James  River  valley  in  eastern  North  and  South  Dakota. f  This  area  is 
supplied  chiefly  from  the  Dakota  sandstone,  a  formation  belonging  to  the 
Cretaceous.  It  outcrops  along  the  slopes  of  the  Black  Hills  and  the  Rocky 
Mountains  at  altitudes  of  3000  or  more  feet  above  sea- level,  furnishing  a 
.percolation  area  estimated  at  about  14,000  square  miles.  From  there  it 
descends  beneath  the  more  recent  formations  of  the  plains,  again  ascends 
slightly,  and  outcrops  at  its  southeastern  edge  along  the  Missouri  and  Sioux 
rivers  at  an  elevation  of  about  1000  feet.  Farther  to  the  north  the  edge  of 
the  stratum  is  covered,  and  the  waters  are  there  largely  prevented  from  escap- 
ing. The  result  is  that  wells  sunk  to  this  stratum  at  points  where  the  surface 
is  low,  as  in  the  James  and  Missouri  river  valleys,  will  have  high  pressures 
(these  are  in  some  cases  as  high  as  150  pounds  per  square  inch  static 
pressure),  but  towards  the  south  and  east  the  pressures  rapidly  fall  off.  Fig. 
23  is  a  section  through  South  Dakota  showing  the  arrangement  of  the  strata.  \ 
The  static  head  at  the  various  wells  is  indicated  by  the  heavy  line. 


FIG.  23. —  SECTION  THROUGH  THE  DAKOTA  ARTESIAN  AREA. 
(From  W.  S.  Paper  No.  67.) 

The  report  of  Mr.  Darton  gives  a  very  instructive  map  showing  the  reduc- 
tion of  pressure  towards  the  eastern  outcrop.     The  hydraulic  slope  amount- 

*  Trans.  Am.  Soc.  C.  E.,  1893,  xxx-  P-  695. 

t  See  report  by  N.  H.  Darton  in  U.  S.  Geolog.  Survey,  1895-96,  p.  603. 

|  From  W.  S.  Paper  No.  67,  U.  S.  G.  S.,  1902. 


I  12 


GROUND-  WA  TER. 


in  general  to  from  4  to  6  feet  per  mile,  which  agrees  fairly  well  with  the  slope 
from  outcrop  to  outcrop.  The  estimated  number  of  wells  in  this  basin  in 
1896  was  400,  of  which  350  were  flowing  wells.  The  total  estimated  yield 
was  232  cubic  feet  per  second.  The  water  is  used  for  irrigation,  water-supply, 
and  power  purposes. 

This  same  Dakota  sandstone  is  the  source  of  supplies  over  small  areas  in 
Nebraska,  Kansas,  and  Colorado,  while  still  other  strata  in  more  recent 
formations  furnish  artesian  water  in  many  places  of  the  Western  plains. 
Among  the  Rocky  Mountains  and  in  California  are  also  many  basins  where 
-artesian  conditions  are  found.  One  such  is  shown  in  Fig.  18,  p.  93. 

In  1890  there  were  altogether  about  9000  artesian  wells  in  the  western 
part  of  the  United  States,  located  for  the  most  part  on  farms  for  water-supply 
and  irrigation  purposes.  Of  this  number  over  3000  were  located  in  Cali- 
fornia. * 

103.  The  Artesian  Area  in  the  Upper  Mississippi  Valley. — A  large  area, 
mentioned  on  p.  109,  in  which  artesian  water  is  extensively  used  for  town 
supplies  is  that  in  northern  Illinois,  eastern  Iowa,  and  southern  Wisconsin. 
Here  the  water  is  furnished  by  several  strata,  chief  of  which  are  the  St.  Peter 
and  the  Potsdam  sandstones.  Fig.  24  is  an  approximate  north  and  south 
section  through  central  Wisconsin  showing  the  general  arrangement  of  the 
water-bearing  strata,  f  The  collecting  area  of  the  Potsdam  strata  is  estimated 
at  14,000  square  miles,  while  that  of  the  St.  Peter  is  only  2000  to  3000. 
These  strata  dip  deeply  below  the  surface  in  southern  Illinois,  and  are  there 
beyond  reach.  They  also  dip  both  eastward  and  westward  from  the  section 


FIG.  24. — SECTION  THROUGH  NORTHERN  ILLINOIS  AND  SOUTHERN  WISCONSIN. 

shown.     The  slope  of  the  surface  of  the  ground  is  quite  small,  and  the  avail- 
able  head   and   the  quantity  obtainable   are  therefore   rather   limited.     At 

*  Eleventh  Census.     Report  on  Irrigation  by  F.  H.  Newell. 

f  From  a  paper  by  D.  W.  Mead,y<?wr.  Assn.  Eng.  Soc.,  1894,  xm.  p.  396. 


LIT  ERA  TUR£.  1 1 3 

Chicago  the  available  head  originally  was  about  100  feet,  but  the  draught  has 
been  so  great  that  now  the  wells  seldom  flow,  and  the  exhaustion  is  felt  for 
several  miles  distant. 

LITERATURE. 

1.  Thiem.      Der    Versuchsbrunnen    fur    die   Wasserversorgung   der   Stadt 

Miinchen.     Jour.  f.  Gasbel.  u.  Wasservers.,  1880,  p.  156. 

2.  Chamberlain.      The    Requisite    and    Qualifying    Conditions    of   Artesian 

Wells.     Report  U.   S.   Geolog.    Survey,  1883-84,  p.  127.     A  com- 
prehensive treatment  of  the  subject. 

3.  Thiem.     Neue    Messungen    natiirlicher    Grundwassergeschwindigkeiten. 

Jour.  f.  Gasbel.  u.  Wasservers.,   1888,  p.  18. 

4.  Harrison.     On  the  Subterranean  Water  in  the  Chalk  Formation  of  the 

Upper  Thames  and  its  Relation  to  the  Supply  of  London.     Proc. 
Inst.  C.  E.,  1890,  cv.  p.  2. 

5.  Artesian-well  Practice  in  the  Western  United  States.     Compiled  from  a 

Government  Report.     Eng.  News,   1891,  xxv.  p.  172  et  seq. 

6.  Stearns.     The  Selection  of  Sources  of  Water-supply.     Jour.  Assn.  Eng. 

Soc.,  1891,  x.  p.  485. 

7.  Report  of  the  Artesian  and  Underflow  Investigation,  1893,  Senate  Doc. 

No.  41.      Relates  to  the  ground-  and  artesian  water  of  the  plains. 

8.  Salbach.      Experiences  had  during  the  last  Twenty-five  Years  with  Water- 

works having  an  Underground  Source  of  Supply.     Trans.  Am.  Soc. 
C.  E.,  1893,  xxx.  p.  293. 

9.  Frtihling.      Handbuch  der  Ingenieurwissenschaften.      Leipzig,  1893,  in. 

Band,  Abteilung  I,  2.  Halite,  pp.    189-212. 

10.  Lubberger.      Die   Quellenbildung    in    den   Verschiedenen   geologischen 

Formationen.     Jour.  f.  Gasbel.  u.  Wasservers.,  1894,  p.  269. 

11.  Mead.      Hydro-geology  of  the  Upper  Mississippi  Valley  and  some  of  the 

Adjoining  Territory.     Jour.  Assn.  Eng.  Soc.,  1894,  xm.  p.  329. 

12.  Lueger.     Die  Wasserversorgung  der   Stadte.    Darmstadt,    1895,    Abteil- 

ung i.     Contains  much  matter  relative    to   ground-water;    also  a 
large  number  of  references. 

13.  The  Development   of  Percolating    Underground    Waters.     Eng.    News, 

1895,  xxxin.  p.  1 1 6. 

14.  Maitland.     The  Geological  Structure   of   the  Extra-Australian  Artesian 

Basins.     Proc.  Royal  Soc.  of  Queensland,  vol.  XIL,  Apr.  17,  1896. 
Relates  to  the  artesian  basins  of  the  United  States. 

15.  Hawes.     Utilizing  a  Spring  as  a  Source  of  Water-supply  for  a  Town. 

Jour.  New  Eng.  W.  W.  Assn.,  1896,  xi.  p.  156. 

1 6.  Darton.     Artesian-well  Prospects  in  the  Atlantic  Coastal  Plain  Region. 

Bulletin  No.  138,  U.  S.  Geolog.  Survey,  1896. 

17.  de  Varona.      History  and  Description  of  the  Water-supply  of  the  City  of 

Brooklyn,  1896.      Brooklyn  Dept.  of  City  Works. 

1 8.  Gilbert.     The   Underground  Water  of   the  Arkansas  Valley  in  Eastern 

Colorado.        Report    U.    S.    Geolog.     Survey,    1895-96,    Part    II. 
P-  557- 

19.  Leverett.     The   Water   Resources    of   Illinois.     Report   U.    S.    Geolog. 

Survey,  1895-96,  Part.  II.  p.  701. 

20.  Darton.     Reports  on  the  Artesian  Areas  of  the  Dakotas.     Reports  U.  S. 

Geolog.  Survey,  1895-96,  1896-97. 


114  GRO  UND -  W 'A  TER. 

21.  Leverett.     The  Water  Resources  of  Indiana  and  Ohio.     Report  U.  S. 

Geolog.  Survey,  1896-97,  p.  419. 

22.  Orton.     The   Rock    Waters   of  Ohio.     Report  U.    S.    Geolog.    Survey, 

1897-98,  p.  633. 

23.  Darton.     Report    on    the   Geology  and  Water  Resources  of  Nebraska 

West  of  the  One  Hundred   and  Third   Meridian.     Report  U.    S. 
Geolog.  Survey,  1897-98,  p.  719. 

24.  King.     Principles  and  Conditions  of  the  Movements  of  Ground-water. 

Report  U.  S.  Geolog.  Survey,  1897-98,  pp.  67-294. 

25.  Slichter.     Theoretical    Investigation    of   the    Motion    of   Ground-water. 

Report  U.   S.   Geolog.   Survey,    1897-98,  pp.    295-384.     Contains 
bibliography. 

26.  Forchheimer.     Wasserbewegung  durch  Boden.     Zeit.  d.  Ver.  Deut.  Ing., 

1901,  XLV.  p.   1736. 

27.  Slichter.     The  Motions  of  Underground  Waters.     W.  S.  Paper  No.  67, 

U.  S.  G.  S.   1902.     Many  other  Water-supply  papers  of  the  U.   S. 
G.  S.  contain  valuable  data  concerning  underflow. 

28.  Slichter.     A  new  Method  of  Determining  the  Velocity  of  Underground 

Water.     Eng.  News,  1902,  XLVII.  p.   151. 

29.  Flow  of  Water  through  Sand.    Discussion.     Trans.  Am.  Soc.  C.  E.,  1902, 

XLVIII.  pp.  277,  302. 

30.  Fournier  and  Magnin.     Sur   la  Vitesse  d'Ecoulement  des  Eaux  Souter- 

raines.     Comptes  Rendus,   1903,  LXXXVI.  p.  910. 

31.  Report  of  the  Commission  on  Additional  Water-supply  of  New  York  City, 

1904,  App.  VH.  p.  619.       Data  on    ground-water  in  Long  Island. 
Eng.  Record,  1903,  XLVIII.  p.  753  ;    Eng.  News,   1903,  L.    p.  573. 

32.  Slichter.     Measurements  of  Underflow  Streams  in  Southern  California. 

Jour.  West.  Soc.  Engrs.   1904,  ix.  p.  632. 

33.  Forchheimer.     Ueber  Voruntersuchungen  fur  Wasserversorgungen     Zeit. 

Oest.  Ing.  u.  Arch.    Ver.  1906,  LVIII.  p.  200. 

34.  Kirchoffer.     The  Improvements  to  the  Water-supplies  of  Marshfield  and 

Waupaca,  Wis.     Eng.  News,   1907,  LVII.  p.   121. 


B.  QUALITY  OF  WATER-SUPPLIES, 

CHAPTER   VIII. 
EXAMINATION   OF   WATER-SUPPLIES. 

104.  Scope  and  Extent  of  Examination. — The  most  important  ex- 
amination of  water  is  that  which  is  made  to  determine  its  potableness 
and  wholesomeness.      Attention  should  of  course  be  given  to  a  water- 
supply  from  other  points  of  view,  but  the  relation  to  disease-dissemina- 
tion is  of  paramount  interest. 

In  determining  by  means  of  a  sanitary  analysis  whether  any  water 
is  suitable  as  a  public  supply,  various  methods  have  been  instituted  as 
knowledge  regarding  these  problems  has  been  broadened.  None  of 
these  methods,  however,  that  have  yet  been  introduced  are  wholly 
satisfactory,  and  the  subject  of  sanitary  water-analysis  is  far  from  being 
reduced  to  terms  of  mathematical  accuracy.  One  prominent  reason 
for  the  unsatisfactory  results  that  are  frequently  found  in  analytical 
work  is  that  many  of  the  determinations  apply  only  indirectly  to  the 
presence  of  specific  disease  organisms.  This  indirect  relation  therefore 
raises  a  question  that  must  be  interpreted  anew  in  each  individual 
instance.  It  calls  for  a  discriminating  judgment  on  the  part  of  the 
analyst.  In  fact  the  data  which  he  collects  do  not  answer  definitely 
and  decisively  the  question  as  to  the  purity  or  pollution  of  a  supply, 
but,  as  Mason  has  well  expressed  it,  it  assists  his  judgment  in  inter- 
preting these  data. 

105.  Necessity  of  Full  Data  in  Interpreting  Conditions. — Concerning 
this  phase  of  the  water-analyst's  work  there  is  a  great  deal  of  miscon- 
ception.    Many  people  think  that  the  withholding  of  all  data  as  to  the 
origin  and  local   conditions   surrounding   the   supply  in   question  will 
enable  the  analyst  to  arrive  at  an  unbiased  opinion.     Some  in  fact  think 
that  such  a  procedure  is  necessary  to  test  his  expert  skill.      They  look 
upon  a  water-analysis  as  something  similar  to  an  assayer's  test  for  gold, 
something  which  can  be  positively  determined.      But  when  there  is 


II 6  EXAMINATION  OF   WATER-SUPPLIES. 

taken  into  consideration  the  wide  range  that  may  exist  in  waters  from 
various  sources,  and  how  the  analytical  results  obtained  in  such  exam- 
inations will  of  necessity  be  interpreted  differently  in  samples  coming 
from  different  regions,  it  is  manifestly  impossible  for  the  analyst  to 
arrive  at  any  satisfactory  judgment  unless  he  is  more  or  less  familiar 
with  all  of  the  data  that  are  intimately  related  to  the  case.  The  char- 
acter of  the  stratum  from  which  the  supply  is  derived,  the  possibility  of 
pollution,  and  the  nature  of  the  same,  the  kind  of  water,  the  conditions 
under  which  the  sample  has  been  secured  and  kept  are  all  questions 
concerning  which  he  should  have  full  and  explicit  knowledge.  Of 
course  it  may  be  possible  in  extreme  cases,  as  with  badly  polluted  or 
exceptionally  pure  waters,  to  determine  their  nature  with  certainty 
from  a  mere  examination,  but  in  the  great  majority  of  cases  where  the 
conditions  are  less  pronounced,  his  judgment  may  be  at  fault  because 
he  is  kept  in  ignorance  of  local  conditions.  A  sample  which  would 
be  regarded  as  satisfactory  for  a  surface-water  might  be  condemned 
from  a  biological  standpoint  if  from  a  well,  while  the  chemist  would 
frequently  reverse  the  conditions  in  testing  certain  artesian  and  surface 
waters.  The  case  has  been  well  compared  to  the  physician  who  is 
able  to  diagnose  any  malady  by  an  examination  of  the  urine  alone,  or 
in  some  cases  by  an  inspection  of  even  a  lock  of  hair.  Such  a 
diagnosis  would  have  but  little  worth  against  the  judgment  of  one  who 
had  studied  the  case  at  first  hand.  This  should  also  be  the  position  of 
the  analyst.  He  should  be  able  to  inspect  the  local  surroundings,  as 
these  frequently  give  evidence  that  may  be  of  more  value  than  the 
analytical  data  secured.  If  not  able  to  secure  the  data  at  first  hand, 
as  full  information  as  possible  as  to  these  facts  should  be  furnished  him. 

106.  Collection  of  Samples. — The  results  obtained  in  the  analysis  of 
waters  are  frequently  misinterpreted  because  of  errors  in  sampling.  It 
is  necessary  in  this,  as  in  all  analytical  work  where  reliance  is  to  be 
placed  on  the  results  obtained  from  an  examination  of  a  comparatively 
small  amount  of  material,  to  have  a  representative  sample;  not  only  as 
to  its  composition,  but  as  to  subsequent  changes  that  may  take  place 
•in  same.  In  sanitary  water-analysis  the  conditions  are  not  as  they 
would  be  in  a  mineral  analysis  of  a  rock  or  an  ore.  The  substances  for 
which  search  is  to  be  made  are  for  the  most  part  living  things,  or  the 
products  of  vital  activity.  Generally  a  water  is  not  in  stable  equilib- 
rium, but  is  constantly  undergoing  changes  which,  if  they  occur 
before  the  analysis  is  made,  may  markedly  affect  the  interpretation 
that  might  be  given  to  the  results. 

In  taking  samples  for  chemical  or  bacteriological  purposes,  certain 


SAMPLES  FOR  ANALYSIS.  1 1/ 

requirements  must  be  observed  that  are  somewhat  different  for  the  two 
purposes  mentioned. 

107.  Samples  for  Chemical  Analysis. — For  a  chemical  sample  take 
a  glass-stoppered  bottle  of  about  one-half  gallon  capacity.  *     Rinse  out 
the  same  thoroughly  so  that  it  is  free  from  dust  or  dirt.    If  it  is  impossi- 
ble to  secure  a  bottle  having  a  glass  stopper,  one  fitted  with  a  new  cork 
may  be  used,   but  it  should  be  very  thoroughly  rinsed  before  using. 
Fill  the  bottle  nearly  full  with  water,  leaving  a  small  bubble  of  air  for 
expansion.      To  protect  the  mouth  of  bottle  in  transit,  tie  over  same  a 
piece  of  cloth.     The  cork  should  not  be  sealed  in  by  using  sealing-wax 
or  paraffin. 

Great  care  should  be  observed  to  secure  a  representative  sample. 
If  from  a  well,  the  water  should  be  pumped  out  so  as  to  remove  that 
which  has  been  standing  in  the  pipe.  In  a  dug  or  open  well  it  may 
even  be  preferable  to  pump  out  enough  so  as  to  remove  at  least  a  part 
of  the  quantity  originally  present  in  the  well  and  thus  allow  a  fresh  supply 
of  ground-water  to  flow  in ;  although  in  cases  of  surface  pollution  the 
withdrawal  of  the  water  in  the  well  diminishes  the  amount  of  polluted 
matter.  If  sample  is  taken  from  a  surface  supply,  the  bottle  should  be 
plunged  beneath  the  surface  before  removing  the  stopper,  so  as  to  prevent 
the  entrance  of  dust-particles  and  other  floating  impurities.  Care  should 
also  be  taken  not  to  draw  the  sample  from  too  near  the  bottom. 

108.  Samples  for  Bacteriological  Analysis. — For   a   bacteriological 
analysis  still  greater  care  must  be  taken  in  order  to  secure  a  represen- 
tative sample ;  and  also  to  lessen  the  changes  that  quickly  occur  in  the 
germ-life  in  a  water.      As  ordinary  glass  receptacles  always  contain 
more  or  less  bacteria  adhering  to  the  inner  wall,  it  is  necessary  first  to 
destroy  these  even  after  the  bottle  has  been  thoroughly  cleaned.     This 
is   done  by  baking  in   a  dry  sterilizer  (hot  oven)   at  a  temperature  of 
about  280-300°  F.  for  one  hour,  or  steaming  in  a  steamer  at  212°  F. 
When  facilities  are  not  at  hand  for  sterilization  by  heat,  the  adherent 
germ-life  can  be  destroyed  by  rinsing  out  the  flask  with  chemical  disin- 
fectants (corrosive  sublimate,  o.  I  per  cent  solution,  carbolic  acid,  5  per 
cent,  or  dilute  mineral  acids).     It  is  then  necessary  of  course  to  remove 
all  trace  of  the  disinfectant,  which  can  be  easily  done  by  rinsing  out 
the  bottle  at  least  four  times  with  the  water  to  be  sampled. 

Every  endeavor  should  be  taken  to  exclude  the  influence  of  extrane- 
ous factors,  and  in  a  bacterial  test  these  are  much  more  numerous  and 
exert  a  more  profound  effect  than  in  chemical  work.  In  a  surface- 

*For  a  full  mineral  analysis  five  gallons  is  generally  taken. 


Il8  EXAMINATION    OF   WATER-SUPPLIES. 

water  the  influence  of  land  contamination  should  always  be  considered. 
Samples  taken  from  a  stream  after  a  rain  where  any  turbidity  has  been 
produced  will  not  be  representative  of  normal  conditions.  In  taking 
samples  from  wells,  the  pump  and  pipe  should  be  thoroughly  washed 
out,  as  bacterial  growth  generally  occurs  in  water  standing  in  the  same. 
Preferably  bacterial  cultures  should  be  made  immediately  after  the 
sample  of  water  is  secured,  as  a  marked  change  occurs  in  the  germ 
content  of  water  stored  for  a  period,  especially  if  temperature  is  rather 
high  (135).  This  multiplication  is  less  in  tightly  stoppered  glass 
bottles  than  in  those  closed  with  cotton,  and  is  less  in  full  bottles  than 
those  partially  filled.  To  lessen  these  changes  as  much  as  possible 
where  it  becomes  necessary  to  transport  samples  any  considerable  dis- 
tance, they  should  be  packed  in  ice,  in  which  condition  growth  will  be 
greatly  retarded.  Not  infrequently  in  samples  so  treated  there  is  a 
diminution  to  be  noted. 

The  bottles  used  to  collect  bacteriological  samples  do  not  materially 
differ  from  those  employed  in  securing  chemical  samples,  except  that 
generally  a  smaller  quantity  of  water  will  suffice,  unless  it  is  desired 
to  filter  a  large  amount  through  a  germ-proof  filter  (Pasteur)  and  in 
this  way  concentrate  the  bacteria.  In  taking  samples  from  deep 
waters,  special  kinds  of  apparatus  have  been  devised  that  permit  of  the 
securing  of  a  sample  uncontaminated  from  that  of  any  other  depth. 

109.  Sanitary  Analysis  of  Water. — Definite  knowledge  of  a  certain 
character  is  often  desired  as  to  the  quality  of  water  for  different  pur- 
poses (manufacturing,  etc.),  but  these  data  do  not  fall  primarily  within 
the  province  of  the  sanitary  engineer.  A  sanitary  analysis  is  the  study 
of  a  water  with  the  view  of  determining  whether  it  now  contains,  has 
contained,  or  is  likely  to  contain,  anything  which  is  detrimental  to  public 
health.  Not  only  must  potable  water  be  free  from  any  taint  of  sus- 
picion that  would  indicate  dangerous  pollution,  but,  at  the  same  time, 
water  should  not  be  objectionable  in  taste  and  appearance.  More- 
over, water-supplies  must  furnish  water  that  is  suitable  for  laundry  and 
general  domestic  use,  although  this  is  not  strictly  a  sanitary  considera- 
tion ;  but  inasmuch  as  a  supply  must  cover  all  purposes  for  which  water 
is  commonly  used,  this  must  also  be  considered. 

It  is  a  notorious  fact  that  the  majority  of  people  mainly  judge  of 
the  quality  of  a  water  by  its  taste  and  appearance.  If  it  is  clear  and 
sparkling  and  is  fresh  in  taste,  they  will  use  it  without  question,  caring 
little  as  to  the  possibility  of  pollution  with  disease  bacteria.  Once  let 
these  physical  conditions  be  altered  and  suspicion  at  once  attaches  itself 
to  the  supply.  This  deep-grounded  opinion  arises  for  the  most  part 


DETECTION  OF  POLLUTION  BY  ADDITION  OF  CHEMICALS.   I  1 9 

from  a  rational  conviction  that  wholesome  water,  especially  that  derived 
from  the  ground,  is  clear  and  sparkling  and  ought  to  remain  so.  If 
for  any  reason  a  change  occurs,  it  signifies  a  variation  in  conditions — 
a  state  to  which  ground-waters  of  first  quality  ought  not  to  be  subject. 
While  this  rule  applies  universally  to  ground-waters  in  wells,  it  is  not 
so  pertinent  to  surface-supplies  or  waters  in  large  distributing  systems 
as  in  large  cities. 

In  determining  the  sanitary  condition  of  a  supply,  a  single  analysis 
is  of  but  little  value,  especially  if  this  is  made  by  one  unfamiliar  with 
local  conditions.  To  be  able  intelligently  to  interpret  conditions  with 
any  marked  degree  of  accuracy,  analyses  should  be  conducted  at  fre- 
quent intervals,  in  order  to  determine  the  stability  of  the  chemical  and 
biological  composition.  A  water-supply  subject  to  sudden  and  con- 
siderable fluctuations  in  these  respects  is  generally  one  that  should  be 
regarded  as  suspicious,  at  least  until  the  cause  of  such  variation  is  satis- 
factorily explained. 

no.  Detection  of  Pollution  by  Addition  of  Chemicals. — Not  infre- 
quently a  simple  qualitative  test  that  can  be  readily  applied  by  the 
non-expert  is  of  considerable  service  in  detecting  a  possible  polluted 
condition  in  a  water-supply.  This  is  generally  done  by  the  addition 
of  some  chemical  substance  to  the  source  from  which  pollution  is  possi- 
ble and  then  determining  whether  the  same  reappears  in  the  water- 
supply.  For  this  purpose  a  number  of  different  chemicals  are  used. 
Those  most  readily  recognized  are  substances  having  a  marked  taste 
or  appearance. 

Nordlinger  recommends  for  this  purpose  saprol,  which  tastes  like 
naphtha  and  is  so  penetrating  that  its  odor  can  be  readily  recognized 
in  proportions  of  I  :  1,000,000,  and  by  taste  in  solutions  of  I  :  2,000,- 
ooo.  Some  of  the  anilin  dyes,  as  fluorescein,  often  color  the  water  in 
such  dilute  solutions  that  a  change  in  color  will  be  recognized  even 
after  filtering  through  a  deep  stratum  of  soil. 

Trillat  *  has  recently  experimented  with  a  large  number  of  these 
dyes  and  finds  that  fluorescein  dissolved  in  alcohol  and  diluted  with 
5  per  cent  ammonia  solution  can  be  detected  by  means  of  a  fluoroscope 
in  proportions  of  I  :  2,000,000,000.  The  fluoroscope  used  is  a  tube 
of  white  glass  three  or  four  feet  long  and  one-half  inch  in  diameter, 
closed  at  one  end  with  a  rubber  cork.  In  such  an  apparatus  natural 
waters  have  a  somber  blue  color  which  changes  to  a  clear  green  if 
fluorescein  is  present.  This  dye  possesses  the  evident  advantage  of 

*  Ann.  Past.,  1899,  xni.  p.  444. 


120  EXAMINATION   OF    WATER-SUPPLIES. 

not  being  precipitated  by  the  soil  ingredients,  a  reaction  that  readily 
occurs  with  most  anilin  dyes  brought  in  contact  with  calcareous  soils. 

Where  chemical  methods  can  be  employed  the  use  of  readily  solu- 
ble salts  as,  NaCl  (common  salt),  permits  of  ready  recognition.  Salts 
of  lithium  are  sometimes  employed.  These  admit  of  detection  in 
inappreciable  quantities  if  the  water  is  examined  by  the  aid  of  a  spec- 
troscope. It  does  not  necessarily  follow  because  these  soluble  salts 
reappear  in  a  water  that  organisms  and  dangerous  pollution  would 
likewise  find  its"  way  through  the  soil  for  an  equal  distance,  for  the 
filtering  power  of  the  soil  if  free  from  actual  channels  would  be  such  as 
to  remove  suspended  particles,  even  no  larger  than  bacteria,  while  salts 
in  solution  would  pass  through  soil  by  diffusion ;  but  nevertheless  these 
methods  are  of  service  in  showing  whether  the  possibility  of  danger 
exists. 

in.  Various  Analytical  Methods. — In  examining  a  water  as  to  its 
suitability  for  public  use,  four  different  kinds  of  tests  can  and  should  be 
applied.  These  are  as  follows: 

Physical  examination. 

Chemical  examination. 

Bacterial  examination. 

Microscopical  examination. 

The  respective  value  of  these  independent  analytical  methods 
differs  much  in  various  instances,  yet  in  the  examination  of  most  waters 
all  of  them  have  a  distinct  value.  The  judgment  arrived  at  as  a  result 
of  these  tests  should  be  interpreted  in  the  light  of  an  actual  inspection 
of  surroundings,  if  possible.  More  and  more,  the  experienced  sani- 
tarian is  coming  to  regard  an  ocular  inspection  as  the  final  court  of 
appeal  to  which  all  analytical  conclusions  should  be  referred. 

112.  Value  of  Different  Methods. — Naturally  the  physical  tests  as  to 
the  character  of  a  water  have  been  noted  for  the  longest  period.  By 
the  aid  of  the  senses  any  one  can  detect  in  water  an  abnormal  appear- 
ance, odor,  or  taste,  if  it  is  at  all  pronounced.  If  such  obtains,  this  is 
generally  sufficient  to  discredit  the  reputation  of  the  supply. 

With  the  determination  of  the  relation  that  exists  between  various 
water-borne  diseases  and  human  fecal  matter,  the  chemical  methods 
of  examination  were  gradually  devised.  These  have  been  slowly  per- 
fected, so  that  at  the  present  time  they  permit  of  the  recognition  of  a 
larger  number  of  factors  that  affect  the  value  of  a  water  than  is  to  be 
determined  in  any  other  single  way.  But  even  the  chemical  method 
of  examination  is  largely  an  indirect  method  of  analysis.  The  presence 
of  nitrites  or  chlorine  in  considerable  quantities  in  a  water  is  not  a 


VALUE   OF  DIFFERENT  METHODS.  121 

source  of  disease  in  and  of  itself,  but  under  natural  conditions  a  water 
revealing  the  presence  of  these  substances  in  large  quantities  is  generally 
one  that  has  been  polluted  with  organic  matter,  possibly  of  fecal  origin. 
So  generally  has  this  indirect  relationship  been  determined  that  the  de- 
tection of  considerable  quantities  of  such  chemical  compounds  as  these 
is  regarded  as  sufficient  evidence  of  sewage  pollution.  It  must  of  course 
be  kept  in  mind  that  sewage  from  healthy  sources  may  be  diluted  to 
such  an  extent  as  to  be  comparatively  harmless ;  but  the  fact  remains 
that  such  sewage  may  suddenly  become  detrimental  by  reason  of  dis- 
ease bacteria  gaining  access  to  the  same,  a  condition  which  is  of  course 
readily  possible  if  even  dilute  sewage  was  to  be  tolerated  in  any  supply 
used  for  potable  purposes. 

Again,  a  distinct  value  of  the  chemical  method  of  analysis  is  that  it 
tells  something  of  the  previous  history  of  the  water.  If  nitrates  are 
present  under  certain  conditions,  it  shows  that  organic  matter  has  had 
access  to  the  water  and  has  undergone  the  decomposition  changes 
incident  to  such  material.  This  may  therefore  represent  a  condition 
of  past  pollution. 

Unfortunately,  on  the  other  hand  it  is  not  always  possible  to  decide 
by  the  chemical  method  as  to  the  origin  of  such  organic  decomposition 
products ;  whether  they  are  associated  with  human  or  animal  sources 
or  perhaps  attributable  to  vegetable  decay.  Often  the  chemical  analy- 
sis is  extended  to  include  incrusting  constituents,  a  determination  of 
the  alkalinity,  the  carbon  dioxid  and  the  iron  dissolved  in  the  water. 
Ordinarily,  though,  these  have  no  special  sanitary  significance,  and  are 
made  to  determine  the  character  of  the  water  from  other  points  of 
view.  Under  certain  conditions,  as  in  filtration  work  where  coagulants 
are  used,  the  determination  of  alkalinity  is  of  sanitary  importance  as  a 
basis  for  the  addition  of  the  coagulating  agent. 

Inasmuch  as  the  direct  causal  agent  concerned  in  the  production  of 
disease  by  the  use  of  impure  water  usually  belongs  to  the  bacteria,  it 
would  be  reasonable  to  suppose  that  a  bacteriological  examination 
would  be  a  direct  method  of  determining  the  quality  of  water,  and  it 
would  therefore  possess  a  value  that  does  not  obtain  in  the  use  of  any 
of  the  indirect  methods.  This  hope,  however,  has  been  only  imper- 
fectly realized  as  yet;  for,  in  the  main,  these  methods  do  not  often 
consist  in  a  direct  search  for  the  specific  disease  organism,  but  in  appre- 
hending the  conditions  that  might  permit  of  the  recognition  of  sewage 
pollution  or  the  possibility  of  infection.  Therefore  these  methods  of 
examination  as  now  used  are  also  to  be  considered  as  indirect.  This 
course  is  rendered  necessary  by  reason  of  the  fact  that  disease  germs 


122  EXAMINATION  OF  WATER-SUPPLIES. 

rarely  exist  in  any  water  in  sufficient  numbers  for  any  considerable 
length  of  time  so  that  they  can  be  readily  recognized;  whereas  if  they 
find  their  way  into  water  through  the  introduction  of  fecal  discharges, 
this  evidence  will  be  apparent  for  a  longer  period  of  time.  The  bac- 
teriological tests  are  also  a  more  sensitive  measure  of  the  changes 
in  the  condition  of  the  water.  By  carefully  controlled  quantitative 
estimates  it  is  thus  possible  to  detect  variations  in  composition  that 
would  remain  unobserved  if  sole  reliance  were  placed  on  other  analytical 
methods.  Again,  the  bacteriological  method  offers  by  far  the  most 
accurate  way  to  determine  the  efficiency  of  filter  practice. 

The  microscopic  examination  of  water  does  not  so  much  concern 
itself  with  a  determination  of  whether  sewage  or  the  possibility  of  such 
pollution  is  actually  present  or  not,  as  it  does  with  the  character  of  the 
minor  organisms  of  a  vegetable  and  animal  nature.  Some  of  these  not 
infrequently  cause  bad  odors  and  tastes  in  waters,  but  for  the  most  part 
they  do  not  have  any  other  sanitary  significance  (183).  Few  are  more 
or  less  distinctive  of  polluted  waters,  and  hence  their  recognition  is  of 
value  in  this  connection. 

PHYSICAL  EXAMINATION    OF  WATER. 

To  the  sanitary  engineer  as  well  as  the  non-technical  individual, 
the  physical  tests  applied  to  any  water  are  of  considerable  importance, 
as  frequently  an  acute  sense  will  be  able  to  determine  by  these  means 
a  water  that  is  unsuitable  for  use. 

113.  Color.  —  A  water  to  be  perfectly  satisfactory  as  to  its  physical 
requirements  should  be  colorless,  free  from  any  turbidity,  undesirable 
odor  or  taste,  and  of  sufficiently  low  temperature  to  be  refreshing. 
Ground-waters  are  for  the  most  part  free  from  color,  but  some  surface- 
waters,  particularly  those  of  swampy  origin,  are  often  highly  colored  by 
the  soluble  organic  matter  that  is  dissolved  in  them.  The  peaty  waters 
of  north  England  and  a  large  number  of  the  streams  draining  the  forest 
areas  of  the  United  States  and  Canada  are  typical  of  this  class.  Water 
colored  from  this  cause  generally  exerts  no  noticeable  effect  on  the 
health  of  persons  using  it. 

In  determining  color,  comparison  with  some  arbitrary  standard  is 
usually  made.*  For  this  purpose  several  standards  have  been  proposed. 
One  of  the  earliest  was  to  use  the  colors  produced  by  the  Nessler 
standards  employed  in  the  estimation  of  ammonia.  With  yellow 

*  The  following  papers  give  a  full  discussion  concerning  the  subject  of  color 
determination:  Jour.  Frank.  Inst.,  1894,  p.  402  ;  Jour.  Am.  Chem.  Soc.,  1896,  xvm. 
pp.  68,  264,  and  484  ;  Jour.  N.  E.  Water-works  Assn.,  1898,  xm.  p.  94. 


PHYSICAL   EXAMINATION  OF   WATER. 

waters,  this  standard  was  fairly  satisfactory.  A  more  recent  and  more 
satisfactory  standard  is  made  by  comparing  waters  with  dilute  solutions 
of  salts  of  platinum  and  cobalt.  By  varying  the  ratio  of-  cobalt  to  plati- 
num it  is  possible  to  simulate  closely  the  hue  of  the  natural  water.  The 
color  is  recorded  in  terms  of  the  platinum,  one  part  of  the  metal  in 
1,000,000  parts  of  water  equalling  one  unit. 

114.  Turbidity.  —  Waters  drawn  from  surface  sources,  particularly 
from  running  streams,  are  often  more  or  less  turbid  from  the  presence 
of  suspended  matter  that  finds  its  way  into  the  drainage-streams  by 
reason  of  the  run-off.  Depending  upon  the  geological  nature  of  the 
watershed,  this  turbidity  may  be  sandy  or  clayey.  If  sandy,  the  actual 
amount  of  suspended  matter  may  be  quite  large  without  making  the 
water  unsightly.  On  the  other  hand,  if  clay  particles  abound,  a  much 
smaller  amount  may  render  the  water  densely  turbid.  Sometimes 
these  particles  are  so  minute  and  of  such  a  gelatinous  nature  that  even 
after  a  long  period  of  quiescence  the  water  remains  more  or  less  cloudy. 

While  turbidity  in  a  water  is  generally  due  to  the  presence  of 
inorganic  matter,  yet  vegetable  growths  at  times  may  render  a  water 
turbid.  Such  troubles  are  generally  seasonal,  due  to  the  increase  of 
these  vegetable  forms  during  the  warmer  months.  Algae,  and  particu- 
larly the  diatoms,  are  most  frequently  concerned  in  such  changes.  In 
iron-containing  waters,  a  turbid  condition  may  be  induced  by  the  pres- 
ence of  the  iron-bacterium,  CrenotJitix  (196),  or  by  simple  chemical 
oxidation  of  the  ferrous  salts  to  ferric  oxid.  Lake  waters,  such  as  those 
of  our  Great  Lakes,  are  relatively  free  from  turbidity,  except  as  dis- 
turbed by  storms.  Rivers  draining  forest  areas  are  generally  quite  clear, 
although  they  may  be  colored  from  dissolved  organic  matter. 

Several  tests  for  turbidity  are  in  use.  The  silica  standard  is  prepared 
from  ground  diatomaceous  earth  that  will  pass  a  2OO-mesh  sieve.  Where 
100  parts  of  silica  per  million  of  water  are  used,  a  platinum  wire  one  mm. 
in  diameter  that  is  just  visible  in  open  air,  100  mm.  below  surface,  gives 
a  turbidity  of  100. 

Another  method  is  the  candle  turbidimeter  *  which  consists  of  a 
graduated  glass  tube  with  a  flat  bottom  enclosed  in  a  metal  case.  This 
is  held  over  an  English  standard  candle  and  so  arranged  that  one  may 
look  vertically  down  through  the  tube,  and  see  the  image  of  the  candle. 
The-  water  is  poured  into  the  tube  until  the  image  of  the  candle  just 
disappears  from  view.  The  tube  is  either  graduated  into  parts  per 
million  of  silica,  or  into  numbers  which  correspond  to  silica  standards. 

*  Made  by  Baker  &  Fox,  83  Schermerhorn  St.,  Brooklyn,  N.  Y. 


124  EXAMINATION  OF    WATER-SUPPLIES. 

Another  method  used  is  to  employ  a  white  disk.  Whipple  employs 
one  8  inches  in  diameter  that  is  painted  black  and  white  alternately. 

115,  Odor  and  Taste, — Normal  waters  should  be  relatively  free  from 
any  pronounced  odors  or  tastes.      The  naturally  pleasant  taste  noted 
in  good  water  is  due  in  the  main  to  the  oxygen   and  CO2  dissolved 
therein.      Some  waters,  particularly  spring-waters,  may  at  times  give 
forth  an  earthy  odor  due  to  the  volatile  substances  absorbed  from  the 
upper  soil  layers.      In  other  cases  they  may  be  so   thoroughly  impreg- 
nated with  various  mineral  ingredients  as  to  possess  a  distinct  taste,  as 
is  the  case  with  salt,  iron,  or  sulfur  springs. 

A  considerable  number  of  the  lower  plant  and  animal  forms  are 
able  to  affect  the  taste  and  odor  of  waters,  especially  open  surface- 
waters.  "  Fishy, "  *  'grassy,"  and  oily  conditions  are  those  most 
frequently  noted.  These  odors  are  not  attributable  so  much  to  the 
decay  of  organic  matter  as  they  are  to  the  growth  of  certain  odor-pro- 
ducing algae  (183).  To  recognize  more  thoroughly  the  odor  of  water, 
it  should  be  warmed  to  about  65°  F.,  the  bottle  remaining  tightly 
corked  until  the  test  is  applied. 

116.  Temperature. — From  the  standpoint  of  the  consumer,  the  tem- 
perature of  a  water  is  considered  of  first  importance.      Naturally  this 
condition  is  determined  by  the  source  of  the  supply.      Surface-waters 
follow  in  general  the  atmospheric  variations,   but,  owing   to  the  high 
specific  heat  of  water,  they  never  show  the  range  to  be  noted  in  the 
atmosphere.      In  winter,  the  temperature  of  water-supplies  may  almost 
reach  the  freezing-point,  while  in  summer  it  frequently  exceeds  80°  F., 
being  as  much  too  warm  at  this  season  as  it  is  too  cold  for  use  in  winter. 
In   quite   large   and  relatively  deep  bodies   of  water  the  temperature 
changes  are  not  so  marked.      In  deep  lakes  protected  from  strong  wind 
action,  the  temperature  of  the  lower  stratum  changes  very  slowly  owing 
to  the  low  conductivity  of  water;  but  in  shallow  waters  the  temperature 
coincides  more  closely  with  that  of  the  mean  atmospheric  temperature. 

Ground-waters  have  a  much  more  uniform  and  lower  mean  tem- 
perature than  waters  exposed  to  the  air.  At  a  depth  of  40-60  feet, 
varying  in  soils  of  different  composition,  the  zone  of  constant  tempera- 
ture is  reached  and  waters  from  this  level  remain  quite  uniform 
throughout  the  year,  ranging  from  48-52°  F.  If  the  temperature  of 
the  supply  is  subject  to  much  fluctuation,  and  especially  if  it  is  above 
these  limits,  it  indicates  a  supply  of  shallow  origin.  Very  deep  wells, 
as  artesian  supplies,  frequently  have  a  considerably  higher  temperature, 
due  to  the  effect  of  the  internal  heat  of  the  earth. 

Often  a  city  supply  that  has  a  suitable  initial  temperature  has  its 


CHEMICAL   EXAMINATION  OF   WATER. 

temperature  raised  to  a  point  where  it  tastes  insipid  because  of  the 
shallow  depth  at  which  the  mains  are  laid,  or  the  long  distance  from 
source  to  place  of  consumption ;  but  usually  the  temperature  as  deliv- 
ered to  consumers  depends  mainly  upon  that  of  the  source.'55' 

Generally  the  temperature  of  ordinary  supplies  derived  from  lakes 
can  be  measured  quite  closely  by  lowering  a  thermometer  in  a  vessel 
of  considerable  capacity.  This  can  be  withdrawn  before  it  materially 
changes.  For  accurate  determination  Warren  and  Whipplef  have 
devised  an  instrument  known  as  the  thermophone,  which  is  practically 
an  electrical  thermometer  of  the  resistance  type.  This  instrument 
permits  of  the  registration  of  the  temperature  at  any  depth. 

117.  Chemical  Reaction, — The  chemical  reaction  of  a  water  is  usually 
slightly  alkaline,  due  to  the  presence  of  calcium  and  magnesium  car- 
bonates ;  in  peaty  waters  the  reaction  is  acid,  caused  by  the  vegetable 
acids  here  found  (humic,  geic,  and  ulmic). 

CHEMICAL   EXAMINATION    OF   WATER. 

118.  Purpose  of  Chemical  Tests. — The  chemical  methods  of  water 
analysis  do  not  seek  to  ferret  out  the  presence  of  any  specific  disease- 
producing  organism.      A  water  may  possibly  be  regarded  as  bad  from 
a  chemical  point  of  view,  and  yet  be  wholly  free  from  disease  organ- 
isms, but  under  ordinary  conditions  the  disease-germs  that  are  dissemi- 
nated by  polluted  water-supplies  generally  find  their  way  into  the  same 
through  the  medium  of  sewage.      Under  these  conditions,   then,   the 
chemist  does  not  test  directly  for  any  specific  microbe,  but  for  sewage 
pollution,  present  or  past.      This  he  does  on  the  basis  that  a  water- 
supply  intended  for  human  use  should  under  no  condition  contain  any 
evidence  of  fecal  pollution.      His  aim,  as  Drown  states,  is  to  discover 
the  origin  and  history  of  the  nitrogen  compounds  in  the  water. 

The  tests  that  the  chemical  analyst  employs  in  passing  judgment 
on  the  sanitary  quality  of  a  water  are  for  the  most  part,  however, 
methods  that  indirectly  permit  him  to  recognize  the  presence  of  living 
organisms  in  the  water.  The  determination  of  organic  matter  by  the 
loss  in  weight  of  total  solids  before  and  after  ignition,  the  presence  of 
nitrites  and  nitrates,  the  amount  of  oxygen  consumed,  the  free  and 
albuminoid  ammonia  present,  are  all  of  them  directly  related  to  organic 
matter  of  vegetable  or  animal  origin. 

119.  Expression  of  Chemical  Data. — Much  confusion  exists  in  the 
interpretation  of  chemical  data  because  no  single  standard  is  recognized 

*  Exam,  of  Water,  1890,  p.  675,  Mass.  Bd.  Health, 
f  Microscopy  of  Drinking-water,  p.  55. 


126  EXAMINATION  OF   WATER-SUPPLIES. 

the  world  over  in  presenting  the  results  of  analytical  work.  The  earlier 
method  of  giving  number  of  grains  per  gallon  *  has  been  for  the  most 
part  supplanted  by  the  method  of  expressing  the  data  either  as  parts 
per  100,000  or  parts  per  million  in  weight,  the  evident  advantage  of 
the  latter  method  being  that  no  computation  is  necessary  where  weight 
is  expressed  in  milligrams,  as  this  gives  parts  per  1,000,000  when 
referred  to  a  liter,  t 

120.  Interpretation  of  Chemical  Data. — It  is  beyond  the  purpose  of 
this  book  to  take  up  methods  of  analysis,  but  the  sanitary  engineer 
should  be  able  at  least  to  interpret  in  a  general  way  the  results  of  such 
analyses. 

Desirable  as  it  would  be  to  have  definite  standards  of  water  analysis 
that  would  apply  to  all  waters,  such  are,  nevertheless,  impossible.  The 
changing  conditions  under  which  various  potable  supplies  occur  make 
it  altogether  out  of  the  question  to  have  a  standard  that  would  be  of 
general  application.  In  the  present  state  of  the  science  there  is  even 
a  lack  of  uniformity  in  interpreting  results,  some  analysts  placing  more 
emphasis  on  one  factor  than  on  another. 

While  a  general  standard  of  purity  is  not  possible,  many  have 
advocated  the  adoption  of  local  standards  that  embrace  a  definite 
geological  formation  in  a  restricted  region.  This  standard  of  course 
could  not  apply  to  all  classes  of  waters  from  even  a  single  region,  but 
would  have  to  be  limited  to  waters  of  the  same  origin,  as  wells,  springs, 
or  streams. 

121.  Total  Solids   and  Character  of  Same. — Ordinarily  a  water  is 
examined  in  an  unfiltered  condition,  but  in  certain  cases  it  is  necessary 
to  differentiate  between  substances  in  solution  and  those  held  in  sus- 
pension.     The  total  solids  of  a  good  water,  including  both  suspended 
and  soluble  matter,  vary  considerably,  depending  upon  the  geological 
formation.      Well-   and   spring-waters   are    naturally  much  higher  in 
soluble  solids  than  surface  supplies. 

The  solids  in  a  water  are  made  up  of  mineral  matter  such  as 
carbonates,  chlorides,  sulfates,  etc.,  together  with  the  organic  matter  of 
vegetable  and  animal  origin.  The  inorganic  ingredients  determine  the 
hardness  of  the  water,  a  characteristic  that  is  generally  determined,  but 
which  is  of  more  economic  than  sanitary  importance.  The  hardness 

*  Conversion  Table. — To  convert  grains  per  Imperial  gallon  (parts  per  70,000)  into 
parts  per  million,  divide  by  7  and  multiply  by  100. 

To  convert  parts  per  million  into  grains  per  gallon,  multiply  by  7  and  divide  by 
joo. 

f  This  standard  is  recommended  by  the  Committee  on  Methods  of  Water  Ex. 
amination  appointed  by  the  American  Association  for  the  Advancement  of  Science. 


CHEMICAL   EXAMINATION  OF   WATER. 

in  a  water  is  temporary  when  it  is  caused  by  carbonates  which  are 
precipitated  upon  heating,  while  the  sulfates  and  chlorides  produce  a 
permanently  hard  water.  A  water  of  moderate  hardness  is  generally 
preferred  by  most  people  to  soft  water  for  drinking  purposes.  Not 
infrequently,  waters  are  so  hard  as  to  be  unsuitable  for  industrial  as 
well  as  domestic  purposes.  In  such  cases  they  can  be  softened  by  the 
aid  of  chemical  treatment  (Chapter  XXIII). 

122.  Loss  on  Ignition, — If  the  evaporated  residue  obtained  in  deter- 
mining the  total  amount  of  solid  matter  is  gradually  heated  to  redness, 
the  organic  matter  is  driven   off  by  degrees.      If  the  ash  is  white,  it 
denotes  the  presence  of  mineral  solids,  although  the  presence  of  iron 
will  tend  to  discolor  the  ash.      If  much  organic  matter    is    present, 
it  blackens  and  the  peculiar  smell  inherent  to   vegetable    or  animal 
substances  may  often  be  detected. 

Peaty  waters  will  naturally  contain  a  considerable  amount  of 
organic  matter,  the  presence  of  which  may  not  be  incompatible  with 
good  water. 

The  relation  between  the  weight  of  the  total  solids  obtained  by 
drying  at  212°  F.  and  the  ash  after  ignition  marks  the  amount  of 
organic  matter,  but  some  mineral  salts  break  up  on  being  heated  and 
so  diminish  the  value  of  this  determination. 

123.  Chlorine. — All  surface-  and  ground -waters  contain  chlorine  in 
variable  proportions,  the  majority  of  the  chlorides  existing  in  the  form 
of  sodium  chloride  (common  salt).      In  certain  regions  which  are  under- 
lain with  salt-bearing  strata,  as  central  New  York  and  Michigan,  the 
chlorine  content  of  the  ground-waters  is  of  course  high.      Proximity  to 
the  ocean  also  increases  appreciably  the  chlorine  of  unpolluted  waters, 
both  those  of  deep  and  surface  character.      This  has  been  strikingly 
shown  in  Massachusetts  and  Connecticut,  where  a  survey  of  these  States 
has  been  made  with  reference  to  this  point.      The  lines  representing 
approximately   equal   amounts    of  chlorine,   called    isochlors,    run,   in 
general,  parallel  with  the  coast.     They  range  from  24  parts  per  million 
on  ocean-engirdled  Cape  Cod  to  .6  part  per  million  in  the  northwest 
portion  of  Massachusetts.     These  data  are  very  valuable  in  determining 
a  local  standard  as  to  the  normal  condition  of  unpolluted  waters  of 
different  regions. 

Chlorine  is  also  a  constant  accompaniment  of  sewage  and  house- 
wastes,  urine  containing  from  0.75  to  I  per  cent  of  the  same.  The 
readiness  with  which  this  element  percolates  into  the  soil,  and  its 
stability,  are  such  that  it  serves  as  a  ready  means  of  determining  whether 
the  ground-water  is  polluted  with  household  or  animal  wastes. 


128  EXAMINATION  OF   WATER-SUPPLIES. 

The  presence  of  no  more  than  normal  amounts  in  a  water  is  there- 
fore good  evidence  that  it  is  unpolluted,  but  the  converse  of  this  does 
not  necessarily  mean  pollution.  Here  is  where  the  necessity  of  addi- 
tional data  is  evident  as  to  the  normal  chlorine  content  of  waters  in  the 
region  under  investigation.  Excluding  chlorine  due  to  salt  deposits 
and  that  derived  from  the  sea,  a  high  content  generally  means  pollution 
with  sewage  or  household  wastes.  Chlorine  in  itself,  however,  may 
be  misleading,  as  it  tells  nothing  of  the  time  of  pollution.  Being  solu- 
ble it  percolates  slowly  into  the  ground,  and  it  by  no  means  follows 
that  disease  bacteria  or  any  other  harmful  substance  is  capable  of  fol- 
lowing it.  Pollution  may  have  occurred  at  some  previous  date  and  the 
organic  matter  undergone  complete  oxidation,  and  yet  the  chlorine 
remains  to  tell  of  past  pollution. 

In  this  way  the  soil  of  inhabited  areas  becomes  gradually  impreg- 
nated, so  that  the  ground- water  of  such  regions  is  generally  much 
higher  in  chlorine  than  that  from  less  thickly  populated  localities. 

The  observations  of  the  Massachusetts  Board  of  Health  indicate 
that  100  persons  to  the  square  mile  will  increase,  on  the  average,  the 
normal  chlorine  of  a  region  about  0.5  part  per  million.  Thresh's* 
estimate  for  England  is  about  0.43  part  per  million  for  the  same 
increase  in  population  per  square  mile. 

124,  Organic  Matter. — Inasmuch  as  the  really  dangerous  substances 
in  a  water  from  a  sanitary  point  of  view  are  organic  in  nature,  the 
determination   of  this   factor  is    of  prime   importance.      The    organic 
material  in  water  may  be  of  either  animal  or  vegetable  origin.      Purely 
vegetable  matter,  as  in  peaty  waters,  may  frequently  be  present  in  excess 
and  still  such  waters  be  perfectly  wholesome.     That  which  is  associated 
with  human  wastes  is  of  course  the  most  dangerous,  but  it  is  not  easy  to 
determine  by  chemical  analysis  the  exact  origin  of  the  organic  matter 
as  to  whether  it  is  derived  from  animal  or  human  sources. 

125.  Free  and  Albuminoid  Ammonia. — Inasmuch  as  the  nitrogen 
content  of  organic  matter  throws  much  light  on  the  character  of  the 
same  as  to  whether  it  is  of  animal  or  vegetable  origin,  a  determination 
of  this  element  in  the  form  of  free  and  albuminoid  ammonia  is  of  great 
service  in  sanitary  chemical  analysis.      In  the  decomposition  of  organic 
matter,  more    or  less  complex  nitrogenous  by-products  are  produced 
that  are  classed  as  albuminoid  in   character.      In   the  more  ultimate 
stages  of  this  disintegration,  the  nitrogen  appears  in  the  form  of  am- 
monia which  may  unite  with  acids  to  form  salts.     These  products  are 
finally  converted  by  other  bacteria  in  nitrites  and  nitrates. 

*  Pearmain  and  Moor,  Chem.  and  Biol.  Analysis  of  Water,  p.  51. 


CHEMICAL   EXAMINATION  OF   WATER.  I2Q 

Albuminoid  and  free  ammonia  therefore  represent  nitrogen  in  the 
earlier  transition  stages,  and  inasmuch  as  these  products  invariably 
accompany  fecal  matter,  their  presence  in  water  is  of  sanitary  signifi- 
cance. 

Waters  may,  however,  contain  considerable  quantities  of  free 
ammonia  under  normal  conditions  and  still  be  entirely  wholesome,  as 
in  peaty  moorland  waters,  in  rain-water,  and  even  in  artesian  wells. 

In  the  case  of  many  ground-waters  the  ammonia  is  probably  due  to 
the  reduction  of  nitrites  and  nitrates  by  reducing  substances  present  in 
the  soil.  Albuminoid  ammonia  should  not  be  present  in  such  waters. 
If  it  is,  it  is  indicative  of  surface  pollution  or  imperfect  filtration.  The 
ratio  between  the  free  and  albuminoid  ammonia  is  of  importance  in 
judging  of  the  character  of  the  organic  matter.  Generally  a  high  ratio 
between  the  albuminoid  and  free  ammonia  in  connection  with  low 
chlorides  and  nitrates  characterizes  vegetable  pollution;  increased 
amounts  of  free  ammonia  with  an  excess  of  the  chlorides,  animal 
matter. 

Something  as  to  the  character  of  the  organic  matter  present  can  be 
told,  according  to  Smart,  by  the  rate  at  which  the  ammonia  is 
evolved,  gradual  evolution  signifying  fresh  pollution,  while  rapid  pro- 
duction shows  the  organic  matter  in  a  more  advanced  state  of  decom- 
position. 

The  necessity  for  early  analysis  is  to  be  observed  in  the  change 
which  the  ammonias  undergo  in  waters  that  are  allowed  to  stand  for 
some  days,  the  free  ammonia  gradually  being  converted  into  nitrites 
and  nitrates.  The  organic  ammonia  is  more  stable,  but  it,  too,  in 
time  breaks  down  and  passes  into  the  ' '  free  ' '  stage  as  a  result  of 
biological  changes. 

126.  Oxygen  Consumption. — Another  method  of  determining  organic 
matter  is  to  find  out  how  much  oxygen  is  required  to  oxidize  the  matter 
present  in  a  water.  Generally  in  a  water  deficient  in  unoxidized  sub- 
stances, as  ferrous  salts,  nitrites,  etc.,  the  carbon  of  organic  matter 
readily  takes  up  oxygen,  so  that  a  determination  of  this  capacity  for  a 
standard  length  of  time  enables  the  amount  of  organic  matter  to  be 
approximately  determined.  This  is  accomplished  by  using  an  acidified 
solution  of  potassium  permanganate.  Often  two  determinations  are 
made;  one  for  10  or  15  minutes,  in  which  the  readily  oxidized  matter, 
as  nitrites,  ferrous  .salts,  and  sulfides,  are  acted  on;  the  other  for  a 
number  of  hours,  during  which  the  less  readily  oxidizable  organic 
matter  will  be  acted  on.  Surface-waters  carrying  suspended  matter, 
or  peaty  waters,  also  show  a  high  oxygen-consuming  capacity. 


130  EXAMINATION  OF   WATER-SUPPLIES. 

127.  Nitrites.  —  Nitrites  represent  nitrogenous  matter  in  an  inter- 
mediate stage  of  decomposition,  and  therefore  their  presence  signifies 
present  pollution  with  organic  matter  in  which  germ-life  is  active,  and 
is,  therefore,  an  unfavorable  symptom  in  water  if  present  in  any  con- 
siderable degree.     This  salt  may  occur  as  a  result  of  the  incomplete 
oxidation  of  ammonia  products  by  the  nitrifying  organisms,  or  it  may 
sometimes  be  formed  by  the  reduction  of  the  more  stable  nitrates  by 
the  denitrifying  bacteria  which  abound  in  decomposing  organic  matter. 
Usually  such  substances  are  absent  in  good  well-waters,  but  if  present 
they  may  be  due  to  reduction  processes,  the  change  often  being  accom- 
plished by  such  mineral  substances  as  ferrous  oxid.     In  such  instances 
the  existence  of  nitrites  may  have   no  sanitary  significance,  as    they 
are  not  likely  to  be  associated  with  disease-producing  bacteria.     The 
presence  of  high  nitrites  and  high  free  ammonia  is  usually  indicative 
of  sewage  pollution  either  in  surface  or  subterranean  waters. 

128.  Nitrates. — These  salts  represent  the  ultimate,  the  final  stage 
into  which  nitrogen  is  changed  by  the  biological  processes  in  soil  and 
water.      In  this  form  nitrogen  is  more  stable,  and  these  salts  therefore 
collect  in  the  soil,  subject  only  to  leaching, 'and  the  use  they  play  in 
the  development  of  the  green  plant.     Their  presence  therefore  may 
indicate    merely    past    pollution,    without  any  present   danger.      Not 
infrequently  deep  wells  may  contain  high    nitrates  without  suspicion 
being   cast  on   the   quality  of  the  water;   but  if  associated  with   free 
ammonia   or   nitrites,    it  is    evidence    of  incomplete   oxidation.      The 
higher  nitrogen  content  of  animal  in  comparison  with  vegetable  matter 
is  generally  betrayed  in  the  amount  of  nitrates  present  in  a  water. 

I2Q0  Summary. — From  the  foregoing  considerations  it  is  manifestly 
impossible  to  determine  the  character  of  a  water  by  the  use  of  a  single 
test.  The  substances  that  accompany  sewage,  which  is  primarily 
dangerous  on  account  of  the  disease-producing  micro-organisms  that  it 
may  contain,  are  so  frequently  found  in  connection  with  waters  that  have 
had  no  opportunity  for  dangerous  pollution,  that  the  analyst  must  use 
the  greatest  care  in  interpreting  the  results  of  an  analysis.  Chlorine 
and  nitrites  as  such,  for  example,  are  not  dangerous  to  human  health, 
but  it  is  because  these  substances  prevail  in  waters  that  are  polluted 
with  dangerous  matter.  If  their  presence  was  characteristic  of  sewage 
only,  then  the  matter  of  sanitary  water-analysis  would  be  reduced  to 
simple  terms,  but  unfortunately  such  is  not  the  case. 

The  most  that  a  chemical  analysis  can  do  is  to  prove  the  presence 
of  organic  matter  that  may  be  a  source  of  pollution.  It  throws  no  light 
on  the  question  as  to  whether  the  same  is  actually  disease-producing 


BACTERIAL    EXAMINATION  OF   WATER  131 

or  not.  Even  though  sewage  is  shown  to  have  polluted  a  water,  this 
does  not  prove  it  to  be  absolutely  dangerous  ;  but  of  course  if  the  possi- 
bility of  pollution  is  present,  all  it  requires  is  the  accident  of  disease  to 
start  an  epidemic.  The  history  of  polluted  waters  is  so  uniformly  in 
harmony  with  the  view  that  typhoid  is  so  distributed  that,  generally 
speaking,  no  further  proof  is  required.  (See  Chapter  X.) 

BACTERIAL  EXAMINATION   OF  WATER. 

130.  Development  of  Methods.  —  Inasmuch  as  the  specific  organisms 
of  disease  which  are  the  really  dangerous  and  polluting  elements  in  a 
water  are  for  the  most  part  included  in  that  group  of  lower  plant-forms 
known  as  the  bacteria,  it  might  naturally  be  thought  that  the  bacterial 
examination  of  a  water  would  quickly  and  satisfactorily  solve  the  ques- 
tion as  to  the  wholesomeness  of  any  supply,  but,  for  reasons  cited  before 
(112),  such  is  not  the  case.     In  comparison  with  the  chemical  methods 
of  investigation,  the  technique  of  bacteriological  methods  is  of  recent 
introduction,  being  based  on  the  epoch-making  discoveries  of  Koch,  made 
in  the  early  eighties.     Much  improvement  has  taken  place  in  the  develop- 
ment and  unification  of  methods,  but  even  yet  analytical  practice  is  not 
as  uniform  as  in  chemical  manipulation.     Bacteriological  methods  have, 
however,  aided  greatly  in  sanitary  analysis,  and  it  is  quite  necessary  that 
they  should  be  utilized  to  gain  the  most  accurate  idea  of  the  sanitary 
quality  of  the  water-supply. 

13 1.  Scope  of  Bacterial  Tests.  —  The  information  to  be  obtained  by 
the  various  bacterial  tests  of  waters  is  principally  as  follows  : 

1.  Detection   of   presence   of   sewage   or   foreign  pollution   which 
may  or  may  not  be  associated  with  infective  matter.     In  this  respect 
the  bacterial  method  embracing  both  quantitative  and  qualitative  work 
is  practically  coordinate  with  the  usual  sanitary  chemical  analysis. 

2.  Quantitative  bacterial  analysis  affords  a  very  sensitive  measure 
for  making  comparative  tests  as  to  distance  to  which  pollution  can  be 
traced  in  a  stream  or  lake,  to  establish  presence  of  leaks  in  submerged 
pipes  and  to  study  effect  of  external  conditions ;  in  fact,  the  determina- 
tion of  many  variations  in  quality.     In  this  respect  it  is  often  a  more 
accurate  measure  than  a  chemical  determination. 

3.  In  the  control  of  the  operation  of  filters  bacterial  analysis  is 
very  much  superior  to  any  other  method,  for  the  reason  that  it  deter- 
mines directly  the  number  of  organisms  before  and  after  filtration.     In 
a  chemical  analysis  so  many  of  the  determinations  are  of  substances 
in  solution  which  readily  pass  a  filter  that  will  hold  back  the  danger- 
ous suspended  matter  (bacteria). 


132  EXAMINATION  OF   WATER-SUPPLIES. 

4.  The  isolation  and  study  of  pathogenic  organisms  from  waters. 
This  is  generally  done  by  combining  cultures  on  artificial  media  with 
animal  experiments. 

132.  Methods  of   Determining   Bacteria.  —  The    bacteria  are   alto- 
gether, too  small  to  permit  of  individual  recognition  by  simple  micro- 
scopic examination  of  water.     Their  number  *  and  general  character  is 
determined  by  adding  the  water  to  be  examined  to  various  kinds  of 
culture  media,  i.e.,  food  substances  in  which  bacteria  can  readily  grow. 
Then  as  each  organism  develops,  a  tiny  aggregation  of  cells  is  produced 
which  is  made  up  of  organisms  that  belong  to  a  single  species.     Such 
amass  of  germs  is  known  as  a  "colony."     A  "pure  culture"  is  then 
made  by  transferring  a  bit  of  this  colony  growth  to  tubes  filled  with 
sterile  culture  media,  on  which  there  appears  in  due  time  the  character- 
istic growth  of  the  germ  in  question.     For  culture  purposes  gelatin  or 
agar  is  used.     Making  a  satisfactory  culture  medium  requires  consider- 
able care,  especially  as  to  the  proper  chemical  reaction  of  the  same. 
Slight  variations  in  this  regard  are  the  cause  of  wide  differences  in 
results,  a  condition  which  readily  explains  the  discrepancies  frequently 
noted  between  different  observers. 

In  studying  the  bacteria  various  liquid  and  other  solid  media  are 
constantly  made  use  of,  for  the  purpose  of  differentiating  species,  but 
the  technique  of  their  preparation  and  use  is  a  question  that  concerns 
the  bacteriologist  rather  than  the  sanitary  engineer. 

133.  Multiplication  of  Bacteria  in  Collected  Sample.  —  If  water  sam- 
ples are  allowed  to  stand  at  ordinary  temperatures  before  cultures  are 
made,  the  accuracy   of  quantitative  determinations   is  much  reduced. 
This  is  due  to  the  very  rapid  growth  of  the  bacteria  in  the  water  after 
sampling.     Often  the  development  in  such  cases  is  enormous  for  a  few 
days,  and  then  a  marked  decrease  may  occur. 

This  fact  has  considerable  bearing  on  the  question  of  analyzing 
water  samples  from  a  distance.  Unquestionably,  for  quantitative  results 
it  is  preferable  to  make  culture-plates  at  the  time  samples  are  collected, 
but  frequently  this  cannot  be  done ;  in  which  case  they  should  be 
maintained  at  low  temperatures  in  full  bottles  during  transportation. 
Franklandf  has  noted  that  in  bottles  closed  with  cotton  stoppers 
growth  was  very  marked,  while  in  tightly  sealed  bottles  filled  completely 
with  water  practically  there  was  no  development. 

*  The  number  of  bacteria  in  any  given  sample  is  invariably  expressed  in  number 
of  organisms  per  cubic  centimeter  (cc.)  which  is  approximately  one-third  of  a  tea- 
spoonful. 

t  Micro-organisms. in  water,  p.  234. 


QUANTITATIVE  BACTERIAL   ANALYSIS.  1 33 

134.  Quantitative  Bacterial  Analysis.  —  Although  too  much  stress 
in  the  past  has  been  laid  on  the  simple  quantitative  enumeration  of 
bacteria  in  a  water  as  an  index  of  its  quality,  yet,  notwithstanding  this, 
the  determination  of  mere  numbers  when  properly  controlled  gives 
considerable  information  concerning  a  water.  It  is  wholly  an  erro- 
neous conception  that  the  quality  of  a  supply  can  be  measured  by  a 
mere  numerical  estimate,  for  there  are  so  many  disturbing  factors  that 
modify  this  determination  that  as  a  standard  it  has  no  value.  Improper 
selection  of  samples,  slight  possible  contamination  with  unsterile  sur- 
faces at  time  of  sampling,  development  of  bacteria  in  sample  before 
cultures  are  prepared,  slight  variations  in  composition  of  media,  differ- 
ent kinds  of  media,  variation  in  incubation  temperature,  in  moisture  of 
culture-dish,  the  possible  error  due  to  small  quantity  of  water  tested, 
and  numerous  other  conditions,  all  contribute  to  make  a  numerical 
estimate  too  delicate  a  measure.  It  is  therefore  impossible  to  propose 
a  quantitative  norm  or  standard,  and  pass  or  reject  waters  on  such 
an  arbitrary  basis. 

Still  the  previous  history  of  a  water  is  to  a  large  extent  revealed  in 
a  bacterial  enumeration  of  a  properly  handled  sample.  Waters  that 
have  come  in  contact  with  the  bacteria-rich  upper  soil-layers  normally 
contain  a  higher  number  than  waters  of  subterranean  origin.  If  then 
the  normal  condition  of  a  water  is  known,  a  marked  quantitative 
increase  indicates  pollution  from  some  outside  source.  The  germ  con- 
tent of  various  waters  noted  in  Chapter  IX  will  indicate  in  a  general 
way  the  normal  condition,  and  will  thus  serve  as  a  basis  for  comparison. 
Generally  speaking,  good  waters  have  relatively  few  bacteria,  but  it 
does  not  necessarily  follow  that  a  water  rich  in  bacteria  is  necessarily 
poor  in  quality. 

For  comparative  estimates  the  quantitative  determination  of  bacteria 
is  often  more  sensitive  than  any  other  method  of  testing.  In  studying 
the  efficiency  of  filter  operations,  or  the  natural  purification  of  a  stream 
or  lake  polluted  with  sewage  or  surface  drainage,  this  method  is  of  great 
value,  as  in  the  case  of  the  Toronto  water-supply,  where  the  intake-pipe 
was  broken  near  shore  and  so  permitted  the  entrance  of  water  from  the 
polluted  shore  region.* 

Where  the  natural  variation  in  germ  content  between  the  two 
waters  compared  is  marked,  this  method  is  of  no  avail,  but  its  usefulness 
decreases  as  the  normal  bacterial  contents  of  the  compared  samples 
approximate  each  other. 

*  Jour.  N.  E.  Water-Works  Assn.,  June,  1896,  p.  211. 


134  EXAMINATION   OF   WATER-SUPPLIES. 

135.  Qualitative     Bacterial     Analysis.  —  While    the    quantitative 
enumeration   of   bacteria  in  any  given  sample  is  under  proper  condi- 
tions an  index  of  some  value  of  the  relation  which  such  sample  bears 
to  the  bacterial  content  of  the  soil,  a  determination  of  the  nature  and 
kind  of  germ  life  present  is  of  much  more  significance  in  studying  the 
quality  of  waters.      The  typhoid  bacillus  and  other  disease-producing 
organisms  that  are  invested  with  special  interest  by  reason  of  the  fact 
that  they  are  disseminated  through  the  medium  of  water-supplies,  find 
their  way  into   such  water-supplies  generally  through   introduction  of 
human  excreta.     The  intestinal  tract  of  animal  life  offers  an  abundant 
opportunity  for  the  development  of  bacteria,  and  it  is  therefore  a  ques- 
tion of  prime  importance  whether  there  is  a  more  or  less  distinctively 
bacterial  flora  of  the  intestine.     Numerous  culture  methods  have  been 
devised  for  the  detection  of  organisms  of  a  sewage  type,  some  of  which 
are  of  material  value  as  approximate  methods  of  determining  the  general 
character  of  any  supply. 

136.  Presumptive  Tests.  — Whipple  has  applied  this  term  to  certain 
tests  which  may  be  used  with  waters  for  the  purpose  of  determining 
approximately  the  origin  and  condition  of  samples  tested.     These  pre- 
sumptive  tests   rest   upon    certain   biological   peculiarities  of   bacteria 
commonly   found  in  the  intestinal   canal.      Bacteria  accustomed  to  a 
habitat  like  the  intestinal  canal  of  warm-blooded  animals  naturally  have 
a  higher  optimum  growing  temperature   than  normal  water  bacteria. 
As  a  class  intestinal  bacteria  are  fermentative   forms   and    generally 
possess  the   property  of  fermenting  certain  sugars  forming  acid  and 
gaseous  by-products. 

137.  Litmus-Lactose  Agar  Test.  —  When  polluted  water  is  added  to 
litmus-lactose   (milk    sugar)   agar   (Wurtz'   method),   and   incubated   at 
body  heat   (98°-ioo°  F.),  abundant  bacterial  growth  takes  place  and 
numerous  strongly  acid  (red)  colonies  develop.     An  unpolluted  supply 
usually  shows  but  slight  development,  and  few,  if  any,   strongly  acid 
colonies,  as  these  types  are  not  as  a  class  able  to  thrive  luxuriantly  at 
blood  heat,  and  produce  the  fermenting  changes  commonly  obtained 
with  fecal  types. 

138.  Fermentation   Tests.  —  Sewage  bacteria   are    usually  able   to 
ferment  dextrose  sugar  solutions  with  the  formation  of  acid  and  gaseous 
by-products.     The  addition  of  varying  quantities  of  water  to  dextrose 
in  fermentation  tubes  enables  the  analyst  to  determine  readily  whether 
gas-generating  bacteria  are  present.     While  these  so-called  presumptive 
tests  may  be  very  readily  applied,  they  should  not  be  regarded  as  final 
in  determining  the  quality  of  water,  especially  in  the  case  of  surface 


SIGNIFICANCE   OF  COLON  BACILLUS.  135 

waters.*  More  value  is  to  be  attached  to  negative  results  than  positive 
findings  as  total  freedom  of  acid-forming  gas-generating  organisms 
in  a  water  sample  of  one  to  ten  cc.  is  only  associated  with  unpolluted 
waters. 

In  case  of  positive  findings  by  these  presumptive  tests,  the  sus- 
pected species  should  be  isolated  and  carefully  studied  by  differential 
methods  in  order  to  determine  with  exactness  the  characteristics  of  the 
organisms. 

139.  Number  of  Species. —  The  bacterial  flora  of  a  water  is  of  course 
subject  to  more  or  less  change,  due  to  variation  in  environmental  fac- 
tors, but  at  any  single  time  the  number  of   species  in  an  unpolluted 
supply,  even  though    of   surface   origin,  is    not  generally   very   large. 
Where   pollution   has    arisen    from    the    introduction    of    decomposing 
material  rich  in  organisms,  not  only  in  number  but  often  in  kind,  the 
number  of    species  present  will  be   increased.     Some  have  placed  an 
arbitrary  limit  on  the  number  that  ought  not  to  be  exceeded  (Migula's 
standard  is  10),-)-  but  such  conclusions  cannot  be  drawn  with  safety. 
The  gelatin-plate  cultures  afford  the  best  medium  for  this  differentiation 
of  species. 

140.  Significance  of  Liquefying  Bacteria.  —  In  growing  on  gelatin 
plates,    bacteria   are    either   able    or    unable    to    render   gelatin   fluid. 
Putrefactive    organisms    are    often    liquefying   species,    and   hence    an 
abnormally  high  percentage  of  liquefying  colonies  is  considered  unde- 
sirable in  a  water.     Such  a  condition  is  certainly  abnormal,  but  it   is 
hardly  possible  to  attach  much  specific  importance  to  this  finding,  for  all 
natural  waters  normally  contain  liquefying  species,  although  they  are 
usually  much  less  numerous  than  the  non-liquefying  forms. 

The  separation  of  individual  species  is  generally  made  from  the 
culture-plates  prepared  for  quantitative  work.  Where  the  colonies  on 
gelatin  or  agar  plates  are  separate  from  each  other,  pure  cultures  of  the 
different  forms  should  be  made.  It  is  not  customary  in  a  sanitary 
examination  to  make  a  detailed  study  of  all  the  different  forms  found 
in  a  water  because  of  the  time  required,  but  if  it  is  desirable  for  future 
study  to  separate  any  species  that  appear  on  the  gelatin  plates,  it  can 
best  be  done  at  this  time. 

141.  Significance  of  Colon  Bacillus.  —  The  significance  of  the  colon 
organism  has  been  a  subject  of  much  discussion.     Originally  this  species 
was  found  in  the  contents  of  the  human  intestine  and  was  thought  to  be 
characteristic  of  fecal  pollution,  but  more  thorough  examination  shows 

*  Gage,  xxxin.  Mass.  Report  397,  1901. 
t  Prac.  Bact,  English  trans.,  p.  167. 


136  EXAMINATION  OF   WATER-SUPPLIES. 

that  it  is  a  common  inhabitant  of  the  intestinal  tract  of  domestic  animals* 
and  lower  forms  of  life.  It  has  been  found  in  abundance  in  the  intesti- 
nal contents  of  mammalia  and  birds.  Amyotf  and  also  Johnson  \  have 
found  it  frequently  in  fishes,  and  Clark  §  has  noted  its  presence  in  shell 
fish,  especially  where  such  water  forms  of  life  were  associated  with 
polluted  waters. 

Some  investigators  have  held  that  the  colon  organism  is  so  ubiquit- 
ously distributed  that  it  possesses  no  value  as  a  sewage  type.  ||  Prescott  ^f 
reports  finding  a  type  on  cereals  and  mill  feeds  that  cannot  be  distin- 
guished from  colon.  Recently,  its  presence  as  an  index  of  fecal  pollu- 
tion has,  therefore,  been  somewhat  discredited,  especially  where  surface 
waters  were  under  consideration. 

In  spite  of  these  differences  of  opinion  among  bacteriologists,  there 
is  no  question  but  that  the  colon  test  properly  performed  is  of  great 
service  in  determining  the  quality  of  any  supply.  In  deciding  the  case 
as  to  whether  pollution  exists  or  not,  much  more  emphasis,  however, 
should  be  laid  on  the  number  of  colon  bacilli  found  than  its  mere  pres- 
ence. Moreover,  in  large  samples  of  water  (100  cc.-5oo  cc.)  positive 
findings  are  not  as  significant  as  in  smaller  samples,  as  the  occasional 
presence  of  this  widely  spread  type  is  not  regarded  as  of  vital  importance. 
If,  however,  a  large  percentage  of  one  cc.  tests  reveal  this  germ,  as 
shown  by  characteristic  cultures  and  reactions,  it  is  generally  regarded 
as  indicating  an  unsafe  condition  in  a  water-supply. 

142.  Importance  of  Other  Sewerage  Types.  — Two  other  forms  have 
been  isolated  from  polluted  waters  that  are  thought  to  bear  a  more  or 
less  direct  relation  to  sewage  pollution.  The  spore-bearing  sewage 
anaerobe  of  Klein,  Bacillus  sporogenes  is  generally  found  in  sewage,  but 
it  is  much  less  abundant  than  the  colon  type.  More  recently  sewage 
streptococci**  have  been  readily  and  abundantly  demonstrated  in 
recently  polluted  waters  f  f  and  in  presumably  unpolluted  waters  they 
are  apparently  absent.  \\ 

*  Moore,  V.  A.,  and  Wright,  F.  R.,  B.  Colt  from  different  species  of  animals, 
Jo.  Bost.  Soc.  Med.  Set.,  iv. :  175,  1900.     Dyar  and  Keith,  Tech.  Quarterly,  vi. :  256, 
1893.    Theobald  Smith,  Cent,  fiir  Bakt.,  xvm. :  494,  1895. 
t  Amyot,  Trans.  A.P.H.A.,  xxvn. :  400,  1901. 
\  Johnson,  Trans.  A.P.H.A.,   xxix. :  385,  1903. 
§  Clark  and  Gage,  Proceedings  A.P.H.A.,  xxix. :  386,  1903. 
||  Weissenfeld,  Zeit.  fur  Hyg.,  xxxv. :  78,  1900. 
1  Prescott,  Medicine,  xi. :  20,  1903. 

**  Streptococci  are  round  celled  types  that  develop  in  long  chains, 
•ft  Houston,  A.  C.,  28  Rep.  Loc.  Govt.  Bd.,  Med.  Supp.  469,  1898.     Winslow  and 
Hunnewell,/0.  Med.  Res.,  vm. :  502,  1902. 
f  J  Winslow  and  Nibecker,  Tech.  Quart.,  xvi. .  227,  1903. 


ANIMAL    TESTS.  137 

143.  Isolation  of  Sewage  Types.  —  The  separation  and  identification 
of  the  sewage  forms  previously  referred  to  requires  considerable  time 
and  previous  experience,  so  that  detailed  examinations  of  this  sort  are 
preferably  to  be  left  to  the  laboratory  expert  rather  than  attempted  by 
the  engineer. 

A  large  number  of  methods  have  been  devised  and  perfected,  in 
most  of  which  the  principle  of  encouraging  the  rapid  growth  of  B.  coli 
is  followed  by  placing  the  water  sample  under  extremely  favorable  con- 
ditions for  the  growth  of  such  species.  By  addition  of  small  quantities 
of  phenol,  growth  of  the  water  bacteria  is  largely  inhibited.  The  addi- 
tion of  readily  fermentable  sugars,  as  dextrose,  permits  of  the  forma- 
tion of  characteristic  gases  (H  and  CO2)  which  are  produced  in  quite 
definite  proportions.  Other  detailed  characters  are  to  be  noted  that 
can  be  found  on  referring  to  any  standard  bacteriological  text-book. 

The  sewage  streptococci  are  also  readily  separated  from  the  pre- 
sumptive cultures.  Prescott  has  shown  that  in  sewage  mixtures  the 
colon  organism  develops  quickly  in  dextrose  broth  and  is  later  sup- 
planted by  the  streptococci.  By  isolating  the  organisms  at  different 
stages  of  development  it  is  possible  to  secure  data  on  presence  of  both 
types  from  the  same  plate.* 

144.  Quantitative   Estimation  of  Colon   Type.  —  The    quantitative 
estimation  of  the  colon  group  is  essential  in  interpreting  the  character 
of  a  supply.     This  was  first  done  by  Theobald  Smith,  who  suggested 
the  inoculation  of  dextrose  fermentation  tubes  with  small  quantities  of 
water,  varying  from  tenths  to  hundredths  of  a  cubic  centimeter.     Devel- 
opment of  gas  in  a  series  of  0.3  cc.  samples,  but  not  in  those  inoculated 
with  o.i  cc.  would  indicate  at  least  3  but  not   10  colon  organisms  per 
cc.     The  mere  presence  occasionally  of  organisms-  of  colon  type  is  not 
considered  as  sufficient   evidence  to  warrant  condemnation  of  water- 
supply,  but  if  this  type  is  found  continuously  and  abundantly,  it  speaks 
strongly  for  evidence  of  pollution. 

145.  Animal  Tests.  —  Some  investigators  f  follow  the  practice  of 
inoculating  directly  into  animals  a  beef-broth  culture  made  by  adding 
water  direct.  Varying  quantities  of  water  are  incubated  in  beef  bouillon 
or  a  peptone  solution,  and  such  animals  as  white  mice,  white  rats, 
guinea-pigs,  doves,  or  rabbits  are  inoculated  with  varying  quantities  of 
the  culture.  The  animal  may  be  killed  by  the  toxic  products  formed 
in  the  culture,  or  it  may  die  from  direct  infection.  This  can  be  readily 


*  Prescott  and  Winslow,  Elem.  Water  Bact.,  p.  104. 
t  Vaughan,  Arch.f.  Hyg.,  xxxvi.,  p.  190. 


138  EXAMINATION  OF  WATER-SUPPLIES. 

determined  .by  making  subcultures  from  such  organs  as  the  liver, 
spleen,  or  kidney.  It  does  not  necessarily  follow  that  organisms 
capable  of  killing  lower  animals  are  able  to  cause  disease  in  the  human, 
but  the  presence  of  such  forms  is  certainly  undesirable  in  water,  and 
supplies  containing  such  are  generally  regarded  as  polluted. 

146.  Concentration  "of  Organisms  in  Water.  —  Where  the  degree  of 
pollution  is  very  slight,  it  oftentimes  becomes  very  difficult  to  determine 
the  presence  of  dangerous  bacteria.     It  must  be  kept  in  mind  that 
water  suitable  for  human  use  is  not  generally  adapted  to  the  growth 
of    specific   pathogenic   bacteria    (222) ;    consequently  such  organisms 
may  be  present  in  such  sparse  numbers  as  to  elude  detection.     Then, 
too,  the  amount  of  water  that  is  ordinarily  subjected  to  a  bacteriological 
test  is  so  small  as  to  render  it  difficult  to  determine  the  presence  of 
occasional  forms. 

Filtration.  —  When  necessary  the  germ  content  of  a  water  can  be 
concentrated  by  filtering  a  relatively  large  quantity  through  a  germ- 
proof  filter  (Pasteur  or  Berkefeld  system.  Cultures  can  then  be  made 
of  the  sediment  adhering  to  the  filter. 

Enrichment  Cultures.  —  Another  method  is  to  incubate  the  water 
sample  under  such  conditions  as  to  composition  of  culture  medium, 
temperature,  etc.,  as  to  cause  certain  types  of  organisms  to  grow 
luxuriantly  while  possibly  holding  back  other  forms  not  desired.  With 
some  bacteria  that  are  of  importance  in  water  analysis  (B.  coli,  Sp. 
cholera  Asiatica),  these  enrichment  methods  are  successfully  used ; 
but  unfortunately  with  the  typhoid  organism  no  method  has  yet 
been  devised  that  can  be  employed  in  a  thoroughly  satisfactory 
manner. 

It  is  evident  that  the  presence  of  distinctively  pathogenic  bacteria 
is  sufficient  to  condemn  any  supply  for  potable  purposes,  but  the  brief 
existence  of  these  forms  in  drinking-waters  makes  it  difficult  to  use 
such  a  standard  for  the  practical  determination  of  the  quality  of  water- 
supplies.  While  of  course  it  would  be  desirable  to  be  able  to  isolate 
such  from  suspected  waters,  yet  direct  proof  of  their  presence  is  not 
necessary  to  justify  a  condemnation  of  a  supply.  If  a  water  shows 
unmistakable  evidences  of  sewage  pollution,  this  in  itself  is  sufficient 
proof  to  warrant  the  same  being  considered  dangerous.  If  this  fact 
is  associated  with  an  increase  in  typhoid  cases  especially,  the  proof 
is  practically  as  strong  as  if  the  typhoid  germ  itself  were  found 
therein. 

147.  Detection  of  Specific  Disease  Bacteria.  —  Not  infrequently  are 
B.  coli  and  the  Proteus  species  found  in  pathological  processes  in  the 


ISOLATION  OF  TYPHOID    ORGANISM.  139 

human  body,  but  nevertheless  these  species  are  not  usually  regarded 
as  pathogenic.  Typhoid  fever,  cholera,  and  dysentery  are  the  distinct- 
ively water-transmitted  diseases.  It  might  with  propriety  be  thought 
that  the  bacterial  method  would  permit  of  their  ready  detection,  but  as 
a  matter  of  fact  it  does  not.  There  are  several  reasons  why  this 
is  so. 

1.  These   pathogenic   microbes   do   not   find   in   drinking-water  a 
favorable   environment.     They  may  live  in  such  a  medium  for  some 
time  (222),  but  it  is  questionable  whether  under  ordinary  conditions 
actual  multiplication  of  cells  takes  place  unless  there  is  a  degree  of 
pollution  due  to  influx  of  organic  matter  that  practically  makes  a  culture 
medium  of  the  water. 

2.  Owing  to  the  considerable  period  of  incubation  (9-14  days  in 
the  case  of  typhoid)  that  must  elapse  between  time  of  infection  and 
appearance  of  outbreak  before  waters  would  ordinarily  be  subjected  to 
examination,  it  is  quite  probable  that  the  disease  germ  may  frequently 
have  disappeared. 

3.  Difficulty  of  detection  is  increased  because  ordinarily  the  amount 
of  water  submitted  to  examination  is  only  a  few  cc.  at  most,  unless  the 
concentration  of  bacterial  life  by  filtration  is  resorted  to. 

4.  Inability,  especially  in  the  case  of  typhoid,  to  find  an  elective 
medium  that  will  permit  of  the  rapid  growth  of  this  germ,  while  at  the 
same  time  retarding  the  development    of  B.  coli  or   other  luxuriant 
congeners. 

These  reasons  suffice  to  show  some  of  the  difficulties  that  the 
analyst  has  to  contend  with  in  this  phase  of  his  work,  yet,  in  spite  of 
these  unfavorable  conditions,  the  presence  of  such  disease  organisms 
as  cholera  and  typhoid  has  been  determined  in  a  considerable  number 
of  cases.  It  should  be  said,  however,  that  in  these  cases  the  conditions 
were  rendered  especially  favorable  through  the  timely  search  and 
facilities  for  such  examinations. 

The  methods  that  are  the  most  successful  in  the  isolation  of  specific 
organisms  are  those  which  permit  of  a  preliminary  development  of  the 
water  sample  under  conditions  extremely  favorable  for  the  growth  of 
the  species  for  which  search  is  made.  The  use  of  elective  media  there- 
fore necessitates  the  introduction  of  different  methods  in  each  case,  for, 
as  a  matter  of  fact,  the  biological  requirements  of  the  different  patho- 
genic bacteria  are  rarely  similar. 

148.  Isolation  of  Typhoid  Organism.  —  Much  endeavor  has  been 
made  by  bacteriologists  to  find  a  suitable  culture  medium  that  would 
permit  of  the  ready  separation  of  the  typhoid  bacillus  from  its  closely 


140  EXAMINATION  OF   WATER-SUPPLIES. 

related  associate,  the  colon  bacillus.  A  number  of  the  technical  methods 
proposed  have  been  discarded  after  a  varying  amount  of  use  when  it  was 
found  that  strains  of  diverse  origin  gave  unsatisfactory  results,  but 
several  are  now  in  quite  general  use  as  furnishing  suitable  means  of 
differentiation.  For  the  most  part,  substances  are  added  which  have  a 
tendency  to  repress  the  development  of  the  saprophytic  water  forms. 
Thus,  the  addition  of  crystal  violet  inhibits  in  large  measure  the  ordi- 
nary types  of  organisms  found  in  water.  The  addition  of  small  quan- 
tities of  phenol  or  carbolic  acid  causes  the  same  effect,  although  the 
action  on  both  the  typhoid  and  colon  organism  is  not  nearly  as  marked. 
The  typhoid  organism  can  be  differentiated  from  the  colon  type  by 
virtue  of  its  difference  in  acid  and  gas  production. 

These  tests  all  require  so  much  experience  that  they  can  only  be 
applied  by  the  expert.  They  are  mentioned  here  as  indicating  that 
proper  tests  for  satisfactory  differentiation  do  exist  and  should  be  used 
where  necessary. 

In  making  the  final  culture  tests  certain  physiological  reactions  serve 
to  distinguish  quite  sharply  the  typhoid  from  the  colon  germ. 

In  contradistinction  to  B.  coli,  B.  typhosus  does  not  ferment  sugar 
solutions  of  any  kind  in  the  fermentation-tube,  neither  does  it  produce 
indol.  It  does  curdle  milk  in  time,  although  the  acid  production  in 
comparison  with  B.  coli  is  much  less.  Since  the  introduction  of  the 
Widal  test  in  diagnosing  typhoid  fever,  it  has  become  possible  to  take 
advantage  of  a  reaction  that  is  so  specific  as  to  be  of  greatest  service. 
If  a  fresh  culture  of  a  genuine  typhoid  organism  is  brought  in  contact 
with  the  blood  of  a  person  suffering  from  this  disease,  the  bacilli  lose 
their  mot'ility  and  become  aggregated  in  clumps,  a  phenomenon  known 
as  the  Widal  reaction,  now  so  extensively  used  in  the  diagnosis  of  this 
disease  in  the  human.  By  taking  advantage  of  this  fact,  it  is  possible 
to  test  a  doubtful  germ  against  a  positively  known  typhoid  blood.  If 
the  isolated  culture  gives  the  Widal  reaction  with  known  typhoid  blood 
and  does  not  with  perfectly  healthy  blood,  the  evidence  as  to  nature  of 
the  organism  in  question  is  practically  decided,  for  when  properly 
examined  the  per  cent  of  accurate  returns  from  this  test  is  very  high, 
approximating  the  possible  limit. 

While  the  typhoid  organism  has  been  reported  as  having  been 
found  more  or  less  frequently  in  waters  of  varying  character,  yet  those 
cases  that  are  reported  prior  to  the  introduction  of  the  "agglutination 
test "  are  now  looked  upon  with  suspicion.* 

*  For  fuller  discussion  of  this  subject,  see  bibliography  appended  to  Chapter  X 
"on  the  detection  of  pathogenic  bacteria  in  water." 


ISOLATION  OF  CHOLERA.  14 1 

149.  Isolation  of  Cholera. — This  organism  grows  with  great  rapidity 
in  alkaline  solutions  of  peptone  and  salt.      By  taking  advantage  of  this 
characteristic  and  incubating  suspected  samples  of  water  at  blood-heat, 
the   cholera   spirillum  can  be   greatly  increased  in  number  so  that  a 
subsequent  examination  of  the  surface  pellicle  will  generally  indicate 
the  presence  of  cholera-like  organisms.      If  positive  microscopic  find- 
ings are  made  by  this  enrichment  method,  the  preparation  of  subcultures 
in  various  media  will  soon  tell  positively  whether  the  organism  is  the 
genuine  "  comma  bacillus  "  of  cholera  or  a  spirillum  of  similar  form,  a 
number  of  which  occur  in  flowing  or  surface  waters.   ' 

The  culture  characters  of  the  cholera  germ  are  fairly  distinctive, 
but  there  are  two  tests  that  are  considered  so  specific  as  greatly  to  aid 
in  diagnosis.  These  are  the  cholera-red  reaction  (indol  test)  and 
Pfeiffer's  phenomenon.  Tests  of  this  character  can  be  made  only  by 
the  bacteriological  expert. 

150.  Disinfection  of  Polluted  Wells  and  Pipes. — It  may  happen  that 
wells  and  water  systems  may  sometimes  become  temporarily  polluted 
with  disease-producing  matter,  without  such  material  continuing  to  find 
its  way  into  the  same.      Under  such  circumstances  it  is  necessary  to 
disinfect  the  water  system  in  such  a  way  as  thoroughly  to  destroy  all 
disease   organisms.       These    methods    should    not    be   interpreted    as 
applying  to  wells  that  are  so  poorly  constructed  that  surface-drainage 
cannot  be  kept  out.      Such  wells  should  be  condemned  and  closed. 
Open  or  dug  wells  are  much  harder  to  disinfect  thoroughly  than  tubular 
wells,  owing  to  the  larger  cubical  content,  but  more  particularly  to  the 
loose  and  open  character  of  the  walls.     Driven  or  drilled  wells  enclosed 
in  iron  pipes  can  be  disinfected  with  little  or  no  difficulty  should  they 
happen  to  become  infected. 

For  this  purpose  several  methods  have  been  used.  Neisser  found 
that  steam  could  be  very  successfully  employed.  A  pressure  of  50-60 
pounds  per  square  inch  succeeded  in  raising  the  temperature  of  a  well 
containing  about  500  gallons  from  50°  to  210°  F.  in  2j  hours.  This 
destroyed  all  trace  of  the  organisms  added,  although  it  did  not  render 
the  well  wholly  sterile. 

A  solution  of  crude  carbolic  and  sulfuric  acid  can  also  be  added  to 
wells  with  good  results.*  In  old  wells,  particularly  those  that  are 
open,  dirt  collects  in  the  bottom,  in  which  case  the  bacteria  retain 
their  vitality  for  some  time.  -The  disappearance  of  the  carbolic  acid  in 
water  can  be  detected  by  applying  ferric  chloride. 

*  Frankel,  Zeit.  /.  Hyg.,  vi.  p.  23. 


142  EXAMINATION   OF    WATER-SUPPLIES. 

Sometimes  it  becomes  necessary  to  disinfect  the  whole  hydrant 
system.  According  to  Stutzer*  0.05  per  cent  solution  of  sulfuric  acid 
suffices  to  destroy  the  cholera  organism  in  1 5  minutes  in  distilled 
water.  As  this  acid  unites  readily  with  the  alkaline  earths  and  iron 
present  in  the  water,  it  is  necessary  to  increase  the  amount  added. 
For  actual  disinfection  work  he  used  0.2  per  cent.  The  acid  solution 
is  allowed  to  fill  the  entire  system,  remain  in  contact  with  the  same  a 
number  of  hours,  and  is  then  flushed  out.  In  disinfecting  the  water- 
mains  after  the  cholera  epidemic  of  Hohenlohehiitte  and  the  typhoid 
outbreak  in  Freiburg,  he  found  that  it  took  about  three  days  to  remove 
all  trace  of  the  acid,  but  the  bacterial  tests  of  the  water  were  then 
found  to  be  wholly  satisfactory. 

151.  Bacterial  Control  of  Filter  Operations. — To  determine  the  effi- 
ciency of  a  filter  system  as  a  means  of  purifying  water-supplies,  the 
bacterial  method  of  examination  has  evident  advantages.  This  is  done 
by  making  a  quantitative  bacterial  examination  of  the  water  before  and 
after  being  applied  to  the  filter.  A  chemical  analysis  generally  shows 
but  little  improvement  because  most  of  the  substances  determined  are 
of  a  soluble  nature,  and  therefore  readily  pass  the  pores  of  the  filter. 
The  real  elements  of  danger  in  water,  however,  are  the  living  organ- 
isms— the  disease  bacteria,  and  these  are  prevented,  by  reason  of  their 
insoluble  nature,  from  passing  through  a  properly  constructed  filter. 

Of  course  there  is  no  differentiation  in  the  filter  between  those 
species  capable  of  producing  disease  and  the  harmless  water  inhabit- 
ants, but  a  determination  of  the  percentage  removed  from  water  during 
filtration  gives  an  approximate  estimate  of  the  degree  -  of  efficiency  of 
the  filtering  process.  At  first  it  was  throught  that  an  enumeration  of 
the  number  of  organisms  in  the  applied  water  and  the  effluent  would 
give  the  exact  extent  of  purification,  but  later  it  was  found  that  some 
bacteria  possess  the  ability  of  growing  in  the  body  of  the  filter  and 
underdrains,  and  so  the  number  in  the  effluent  may  not  represent  the 
actual  number  passing  the  filter. 

Later  the  custom  was  introduced  of  applying  cultures  of  some 
specific  kinds  of  bacteria  not  normally  found  in  the  filter  sand,  and 
determining  the  number  of  such  organisms  in  the  effluent.  Bacillus 
prodigiosus,  one  of  the  most  characteristic  pigment-producing  bacteria, 
has  been  used  for  this  purpose  to  a  considerable  extent,  but  of  late 
years,  B.  coli  communis  f  has  been  more  extensively  employed  because 

*  Zeit.  f.  Hyg.,  XIV.  p.  116. 

f  Clark  and  Gage,/<?«r.  Bost.  Soc.  Med.  Sc.,  1900,  iv.  p.  172. 


MICROSCOPICAL   EXAMINATION  OF   WATER.  143 

of  its  closer  relation  to  disease  bacteria  and  the  fact  that  it  is  in  a  sense 
an  index  of  fecal  pollution. 

The  importance  of  a  careful  examination  of  filter-works  by  this 
method  is  especially  recognized  in  Germany,  where  every  municipality 
using  sand-filtered  water  is  obliged  to  make  frequent  reports,  especially 
on  the  bacterial  results,  to  the  Imperial  Board  of  Health,  as  to  the 
working  of  the  filters. 

MICROSCOPICAL   EXAMINATION   OF   WATER. 

152.  Scope  of  Microscopic  Examinations.  —  In  the  microscopical 
examination  of  water  a  determination  of  the  suspended  matter  other 
than  bacteria  is  generally  included.  This  may  embrace  particles  of 
inorganic  as  well  as  of  organic  origin.  An  opalescent  water  may 
sometimes  be  caused  by  extremely  fine  fragments  of  clay  that  may 
even  be  so  small  as  to  pass  a  filter.  Quartz  splinters  or  particles  of 
iron  oxide  also  not  infrequently  occur.  These  inorganic  materials  have, 
however,  no  sanitary  significance,  but  their  recognition  becomes  a 
matter  of  import  only  as  explaining  the  physical  condition  of  water. 

Of  far  more  importance,  is  the  material  of  organic  origin.  Much 
may  be  learned  of  the  nature  of  a  water  and  its  possible  sources  of 
pollution  by  a  microscopic  examination,  which  generally  permits  of  a 
differentiation  between  matters  of  animal  and  vegetable  character.  A 
recognition  of  any  fibers,  such  as  cotton,  wool,  or  flax,  starch  grains, 
and  undigested  muscular  tissue  indicates  a  source  of  pollution  generally 
due  to  household  wastes. 

In  matter  of  distinctively  fecal  origin  it  is  possible  that  eggs  of  some 
of  the  intestinal  parasites  of  man  and  animals  may  be  present.  Many 
of  these  retain  their  reproductive  powers  for  a  long  time,  but  fortunately 
are  unable  to  develop  in  man  directly,  requiring  an  intermediate  host 

(201). 

In  addition  to  such  microscopic  findings  as  reveal  the  presence  of 
suspended  particles  that  are  often  closely  related  to  house-refuse,  there 
are  a  large  number  of  living  organisms  whose  natural  habitat  is  that  of 
water.  These  may  be  either  animal  or  vegetal  (183).  Generally  speak- 
ing, their  presence  in  water-supplies  is  not  such  as  to  render  the  water 
dangerous  to  human  health ;  *  but  not  infrequently  the  physical  quali- 
ties of  the  water  (taste,  odor,  color)  may  be  profoundly  modified  by 
their  presence.  As  Whipple  well  says,  bacteria  may  render  a  water 
unsafe,  but  other  microscopic  organisms  are  likely  to  make  it  unsavory. 

*  Neisser,  Zeit.  f.  ffyg.t  xxn.  p.  475. 


144  EXAMINATION-  OF   WATER-SUPPLIES. 

A  direct  microscopical  examination  will  not  generally  reveal  many 
forms  unless  precautions  are  taken  to  concentrate  the  same  in  a  small 
volume.  For  this  purpose  plain  sedimentation  will  not  suffice,  but  a 
method  of  filtering  large  quantities  of  a  water  through  sand  has  been 
generally  adopted  (Sedgwick-Rafter  method).* 

In  many  waters  organisms  of  this  class  occur  only  sparingly,  or 
they  possess  no  disagreeable  properties  that  impair  the  quality  of  the 
water ;  hence  their  presence  is  of  no  particular  import.  In  other  cases 
certain  species  are  so  abundant  that  the  quality  .of  the  water  is  dis- 
tinctly injured  by  their  presence. 

Difficulties  of  this  sort  are  quite  apt  to  occur  in  stored  waters,  as  in 
ponds  or  reservoirs,  for  the  access  of  light  is  necessary  for  the  develop- 
ment of  these  plant-forms.  Filtered  or  ground-waters  are  very  prone 
to  develop  these  troubles  unless  reservoirs  are  covered. 

153.  Direct    Microscopic    Examination    in    Filtration-work.  —  The 
microscopical  method  of  examination  is  sometimes  of  service  in  com- 
paring waters,  as  in  the  case  of  sand-filters  or  in  filtration-galleries. 
One  of  the  writers  once  had   an    opportunity  successfully  to   use  this 
method  in  determining  the  presence  of  a  leak  in  a  submerged  pipe, 
the  outer  water  being  a  surface-water  and  therefore  containing  algae. 
In    determining    the    efficiency    of    filtration    in    filter-galleries,   it    is 
necessary  to  use  freshly  filtered  waters,  as  microscopic  organisms  are 
likely  to    develop  rapidly  in  such  waters  open  to  the    sunlight.      In 
Taunton,  Mass.,   trouble  was  experienced  in  the  water  from  a  filter- 
gallery  from  the  growth  of  both  Asterionella  and  Dinobryon  (183). 

SANITARY   SURVEYS. 

154.  Object  and  Value. — The  normal  condition  of  the  water-supply 
of  different  regions  is  subject  to  considerable  variation.      Even  that  of 
the  ground-water,  which  is  generally  supposed  to  be  more  stable,  fluc- 
tuates in   different  parts  of  the  country  with  reference  to  many  of  its 
constituents.     In  some  cases  local  causes  are  operative  in  changing  the 
nature  of  the  supply,  as  in  the  case  of  hard  waters  in  limestone  regions. 
The  same  holds  true  with   reference  to  the  proximity  of  the  sea,  the 
chlorine  content  gradually  diminishing  as  the  distance  from  the  sea 
increases  (123). 

In  different  States  these  sanitary  water-surveys  are  being  taken  up 
by  the  respective  Health  Boards,  and  the  normal  condition  of  the 
water-supplies  determined.  These  afford  a  -basis  for  comparison  that 

*  For  details  of  apparatus  and  use,  see  Whipple's  Microscopy  of  Drinking-water, 
P.  15- 


SANITARY  SURVEYS.  145 

enables  the  analyst  to  judge  more  accurately  as  to  whether  any  water 
he  is  testing  is  abnormal  or  not  for  the  region  from  which  the  sample 
comes. 

Not  only  are  these  sanitary  surveys  being  made  of  the  ground- 
water  supplies,  but  the  surface-waters  are  now  receiving  considerable 
attention.  The  importance  of  this  is  readily  recognized  when  one  con- 
siders that  the  supplies  for  our  larger  municipalities  must  of  necessity 
be  drawn  from  open  waters,  as  these  are  often  the  only  adequate 
sources  that  can  be  used.  With  the  steady  growth  in  our  urban  popu- 
lations and  the  consequent  increased  danger  of  pollution,  it  becomes 
more  and  more  necessary  to  secure  these  supplies  from  distant  sources 
that  are  free  from  pollution,  or  to  purify  those  that  are  more  available 
and  more  likely  to  be  polluted. 

To  keep  close  check  on  the  effect  that  the  constant  increase  in 
population  has,  it  is  necessary  to  know  the  normal  conditions  of  a 
water-supply,  both  chemically  and  bacteriologically.  If  these  surveys 
are  made  before  the  sources  are  polluted,  then  a  standard  of  compari- 
son can  be  had  from  which  the  effect  of  a  growing  population  can  be 
determined.  For  instance,  the  Massachusetts  and  the  English  sanitary 
authorities  estimate  that  the  increase  in  chlorine  content  is  between 
.4  and  .5  part  per  million  for  an  increase  of  every  100  persons  per 
square  mile. 

The  absolute  necessity  of  thus  determining  the  quality  of  waters 
that  are  to  serve  as  sources  of  supply  for  large  cities  is  evident,  but 
these  sanitary  surveys  are  now  being  extended  so  as  to  include  entire 
river  systems.  Several  of  the  States,  as  Ohio,  Illinois  and  Minnesota, 
are  engaged  in  making  a  study  of  the  surface  waters  within  their 
limits.  Cities  situated  on  large  streams  very  often  use  these  as  natural 
drainage-channels  for  sewage  disposal.  The  consequence  is  that  the 
pollution  in  such  streams  is  constantly  increasing,  so  that  the  municipal- 
ities situated  farther  down-stream  are  in  danger  of  having  their  most 
available  source  of  water-supply  polluted  from  the  wastes  of  other  towns. 
It  is  true  that  there  is  a  natural  purification  process  (168)  going  on  in 
such  rivers,  but  the  question  is  always  pertinent  as  to  whether  such 
natural  processes  are  wholly  able  to  purify  the  water.  Mere  loss  in 
turbidity  is  no  criterion  to  depend  upon  in  settling  this  question.  To 
obtain  a  basis  from  which  to  determine  whether  conditions  are  materially 
changed  as  density  of  population  increases,  these  sanitary  surveys  are 
of  great  value,  but  they  should  always  embrace  a  chemical  and  bac- 
teriological examination  and  preferably  engineering  data  should  also  be 
accumulated 


146  EXAMINATION  OF  WATER-SUPPLIES. 

LITERATURE. 

For  a  more  detailed  consideration  of  different  phases  of  sanitary  analysis, 

reference  may  be  made  to  the  following  list.     This  list  is  not  intended  to  be 

exhaustive,  but  merely  comprehensive'  enough  to  direct  the  sanitary  engineer 

to  the  more  important  publications  relating  to  the  sanitary  analysis  of  water, 

and  the  interpretation  of  such  work.     The  technical  water  analyst  will  need  to 

consult  much  of  the  chemical  and  bacteriological  periodical  literature  in 'order 

to  learn  of  methods  available  for  his  work. 

Questions  of  technique  are  considered  more  or  less  in  detail  in  all  of  the 

following  books : 

P.  &  G.  C.  Frankland.     Micro-organisms  in  Water.     1894. 

A  resume  of  the  bacteriological  phase  of  the  subject,  including 
a  description  of  over  200  species  of  bacteria  found  in  waters. 

Tiemann-Gaertner.  Handbuch  d.  Untersuchung  u.  Beurtheilung  d.  Wasser, 
Vierte  Auflage.  1895. 

A  complete  handbook  on  matters  relating  to  both  chemical  and 
bacteriological  examination  of  water-supplies. 

Loeffler,  Oesten  and  Sendtner.      Wasserversorgung,  Wasseruntersuchung  u. 
Wasserbeurtheilung.     1896.     (In  Weyl's  Handbuch  der  Hygiene.) 
Very  useful  to  the  engineer  as  well  as  the  water  analyst. 

Leffmann  and  Beam.  Examination  of  Water  for  Sanitary  and  Technical  Pur- 
poses. 1895. 

Confined  to  the  chemistry  of  the  subject. 

Pearmain  and  Moor.     Chemical  and  Biological  Analysis  of  Water.     1899. 

Mason.     Examination  of  Water.     1899. 

A  revised  reprint  of  two  chapters  on  chemical  and  bacteriological 
examination  of  water  included  in  his  larger,  more  general  work  on 
Water-supply  which  appeared  in  1896. 

Fuller,  G.  W.  Water  Purification  at  Louisville.  1898;  also,  —  Report  on 
Water  Filtration  at  Cincinnati.  1899. 

While  primarily  concerned  with  filtration  experiments,  yet  valu- 
able for  full  exposition  of  analytical  methods. 

Hill,  John  W.  Public  Water-supplies,  1898.  Although  written  from  the 
general  engineering  point  of  view,  this  work  contains  valuable  data 
that  will  be  of  use  not  only  to  the  general  student  but  the  technical 
analyst  as  well. 

Williston,  Smith,  Lee,  and  Foote.  Rept.  on  Exam,  of  Conn.  Water-supplies. 
14  Rept.  Conn.  Bd.  Health,  1891,  p.  231. 

Whipple.     The  Microscopy  of  Drinking-water.     1899. 

A  most  complete  presentation  of  the  relation  of  microscopic 
organisms  other  than  the  bacteria  to  water-supplies,  including  a 
classification  of  such  organisms  as  far  as  genera.  An  indispensable 
book  to  the  student  of  this  phase  of  water  investigation. 

Savage,  W.  G.     Water  Bacteriology,  1907. 

Sedgwick,  W.  T.     Principles  of  Sanitary  Science  and  Public  Health. 

A  general  exposition  on  hygiene,  but  includes  several  excellent 
chapters  on  the  relation  of  water  as  a  vehicle  of  infectious  diseases. 

Horrock,  W.  H.  An  Introduction  to  the  Bacteriological  Examination  of 
Water,  1901. 

Whipple,  George  C.  The  Value  of  Pure  Water  and  Study  of  the  Different 
Characteristics  of  Water  and  What  They  Cost  the  Consumer,  1907. 


LITERATURE.  147 

Prescott  and  Winslow.     The  Elements  of  Water  Bacteriology. 

An  excellent  up-to-date  presentation  of   the  subject   from   the 
bacteriological  point  of  view.     Second  Edition,  1908. 
The  Bibliography  of  analytical  methods  of  water  analysis  is  quite  volumi- 
nous, and  widely  scattered  in  numerous  scientific  journals,  as  well  as  more  tech- 
nical publications.     Besides  the  references  already  given  as  foot-notes  to  the 
text,  the  reader  is  referred  to  the  following  list  of  papers  that  includes  those 
of   general   interest,  as   well   as   some  that  relate  more  specifically  to  the 
technique  of  water  examination  : 
Annual  Reports  of  the  Massachusetts  State  Board  of  Health. 

The  State  Board  of  Health  of  Massachusetts  has  for  a  number 
of  years  carried  on  extensive  experimental  researches  on  water  and 
sewage  as  well  as  methods  of  control  of  both.  The  publications  of 
this  Board  form  one  of  the  most  valuable  contributions  to  the  litera- 
ture of  water  analysis  and  should  be  carefully  studied  by  every 
student  of  this  subject. 

Report  of  Committee  on  Standard  Methods  of  Water  Analysis  of  the  Ameri- 
can Public  Health  Association. 

This  Association  appointed  a  committee  in  1897  to  formulate 
methods  of  procedure  relating  to  water  examinations.  This  report 
published  in  the  transactions  of  the  American  Public  Health  Asso- 
ciation, Vol.  XXVII,  1902,  forms  the  basis  of  laboratory  procedures 
relating  to  physical,  microscopical,  chemical  and  bacteriological 
methods  of  water  examinations. 

Frankland,  Percy.     The  Hygienic  Value  of  the  Bacteriological  Examination 
of   Water.     Trans.  7th  Internat.  Cong,  of   Hygiene  and  Demog., 
London,  1891. 
Kruse,  W.     Kritische-u.  experimentelle  Beitraege  z.  hygien.     Beurtheilung 

d.  Wassers.     Zeit.  f.  Hyg.,  1894,  xvn.  p.  i. 
Korn    and    Kammann.     The    Hamburger   test  for   Pollution.     Gesundheits 

Ingenieur,  March  16,  1907. 
Winslow,  C.  E.  A.     Bacteriological  Analysis  of  Water  and  Its  Interpretation. 

Jour.  N.  E.  W.  W.  Assn.,  December,  1901. 
Clark  and  Gage.     Value  of  Tests  for  Bacteria  of  Special  Types  as  an  Index 

of  Pollution.     Report  Mass.  Board  of  Health,  1902. 
Whipple,  George  C.     Practical  Value   of  Presumptive   Tests  for   B.  coli  in 

Water.     Tech.  Quart.     March.  1903. 
Hesse,  W.  and  Niedner.     Methods   of   Bacteriological   Water    Examination. 

Zeit.  f.  Hyg.  xxix.  p.  454,  1898. 

Hill  and  Ellms.  Apparatus  for  Collection  of  Water  Samples  for  Chemical, 
Microscopical,  and  Bacteriological  Analysis.  Trans.  American 
Public  Health  Association,  xxm.  p.  193,  1898. 

Houston,  A.  C.  Value  of  Examination  of  Water  for  Streptococci  and  Staphy- 
lococci.  Supp.  to  29th  Report  L.  G.  B.  of  England  containing 
Report  of  Med.  Off.  for  1899-1900,  p.  458. 

MacConkey.     Experiments  on  differentiation  of  B.  coli  and  B.  typhosus  by 
use  of  sugars  and  bile  salts.     Thompson-Yates  Laboratory,  Report 
in.  p.  41,  1900,  also  ibid.  iv.  p.  151,  1901. 
Winslow.      Bacteriological    Examination    of   Water    and    Its    Interpretation. 

Jour.  N.  E.  W.  W.  Assn.,  xv.  p.  459,  1901. 

Winslow  and  Nibecker.  Significance  of  Bacteriological  Methods  in  Sanitary 
Water  Analysis.  Tech.  Qu.,  xvi.  p.  227,  1903. 


148  EXAMINATION  OF   WATER-SUPPLIES. 

Sanitary  Surveys.  Sanitary  surveys  of  individual  streams,  watersheds 
furnishing  municipal  supplies,  and  in  some  cases  general  state  surveys  have 
been  or  are  being  made,  generally  under  public  auspices.  In  some  cases  these 
surveys  have  been  undertaken  from  the  chemical  point  of  view ;  in  other 
instances  both  chemical  and  bacteriological  examinations  have  been  made. 

The  most  extensive  work  yet  performed  is  that  done  under  the  auspices  of 
the  Massachusetts  State  Board  of  Health.  (See  Report  on  Exam,  of  Water- 
supplies,  1890  et  seg,) 

Similar  examinations  have  also  been  made  in  Connecticut  (18  Rept.  Conn. 
Bd.  Health,  1895,  p.  230). 

In  New  York  a  careful  sanitary  survey  has  been  made  of  the  Croton  water- 
shed, the  base  of  supply  for  New  York  City  (9  Rept.  N.  Y.  State  Bd.  Health, 
1889,  p.  189)  ;  also  a  chemical  and  bacteriological  study  of  the  Mohawk- 
Hudson  valleys  (12  and  13  Rept.  N.  Y.  State  Bd.  Health). 

Similar  surveys  were  begun  by  the  Ohio  Bd.  of  Health  in  1897.  Two 
reports  have  already  been  issued  (1897  and  1900),  embracing  the  results 
obtained  in  the  study  of  five  of  the  larger  river  systems  of  the  State. 

In  the  State  of  Illinois  the  State  Board  of  Health  is  making  a  chemical  sur- 
vey of  the  water-supplies.  (Report  published  1897.) 

Report  of  Streams.  Examinations  of  waters  between  Lake  Michigan 
at  Chicago  and  the  Mississippi  River  at  St.  Louis  issued  by  the  Sanitary 
District  of  Chicago,  1902. 

A  complete  study  of  the  biological  and  chemical  relations  of  these  waters 
made  prior  to  the  opening  of  the  Chicago  Drainage  Canal. 


CHAPTER  IX. 
QUALITY   OF   WATER. 

155.  Importance  of  Quality. — In  securing  a  water-supply  for  public 
or  for  private  use,  the  question  of  quality  is  of  supreme  importance. 
An  adequate  or  copious  supply  is  not  so  much  to  be  desired  if  it  means 
that  quantity  must  be  purchased   at  the  expense  of  quality.      In  this 
respect  European  cities  are  much  ahead  of  American  municipalities. 
The  per  capita  consumption  in  this  country  is  greatly  in  excess  of  that 
of  Europe,    but  in   the   matter   of  quality  they   frequently  excel   our 
standards. 

Pure  water  from  the  standpoint  of  the  chemist  is  not  to  be  found 
in  nature;  neither  is  it  desirable  that  such  should  be  furnished  for 
general  purposes,  for  the  presence  of  certain  salts  in  water  makes  it 
more  palatable  and  better  for  use  than  distilled  water.  The  origin  of 
all  water-supplies  is  primarily  to  be  traced  to  the  rainfall,  although  it 
by  no  means  follows  that  the  supply  utilized  in  any  particular  region  is 
derived  from  the  precipitation  in  that  immediate  locality. 

As  has  previously  been  shown,  the  rainfall  is  either  evaporated  from 
the  surface  of  the  earth,  runs  off,  or  percolates  into  the  ground.  Only 
that  which  remains  on  the  surface  or  in  the  soil  is  of  any  avail  as  a 
source  for  water-supplies.  Between  the  surface  "  run-off"  and  that 
which  flows  beneath  the  surface  there  is  a  constant  interchange  which 
exerts  its  effect  on  the  quality  of  the  water. 

156.  Changes  in  Quality  Determined  by  Course  of  Water. — As   it 
condenses  in  the  atmosphere  and  falls  to  the  earth's  surface,  it  begins 
to  absorb  impurities ;  and  its  whole  history  from  the  time  it  is  precipi- 
tated until  it  finally  finds  its  way  back  into  the  air  through  evaporation 
is  marked  by  the  absorption  of  substances  which  pass  into  solution  or 
are  held  in  suspension,  as  well  as  the  precipitation  or  elimination  of 
the  same  or  other  ingredients.      Some  of  these  changes  are  harmless 
so  far  as  affecting  the  ordinary  use  to  which  water  is  put;  others  are  of 

149 


150  QUALITY   OF   WATER. 

much  consequence,   depending  upon  the  requirements    to  which  the 
water-supply  is  subjected. 

157.  Requirements  as  to  Quality. — The  ordinary  purposes  to  which 
water-supplies  for  human  use  are  put  may  be  included  under  the  fol- 
lowing heads:   potable,  domestic,  and  manufacturing  uses.      So  far  as 
quality  is  concerned,  the  conditions  desired  for  each  purpose  do  not 
necessarily  coincide. 

158.  Potableness. — A  suitable  supply  for  drinking  purposes  should 
not  only  be   pleasant    and   palatable,   but    if  possible  free   from    any 
marked  color  or  turbidity.      While  these  latter  requirements  are  desir- 
able, they  are  not  obligatory,   for  experience  has  fully  demonstrated 
that  many  peaty  supplies   and   often   turbid  waters  may  be  used  with 
perfect  safety.      A  potable  water  should  not   be   excessively  charged 
with   mineral   matter   in   solution.      Mineral   waters   have  a   value   for 
medicinal  purposes,  but  not  as  general   supplies.      It  has  long  been  a 
disputed  question  as  to  the   effect  on   human  health  of  waters  heavily 
loaded  with   dissolved   mineral   matter.      A  common  prejudice   exists 
against  the  use  of  very  hard  waters,  as  they  are   supposed  to  result  in 
the  production  of  various  diseases,  as  urinary  calculi,  goitre,  cretinism, 
etc.,  but  there  are  no  established  scientific  data  that  would  positively 
confirm  such  an  opinion.      It  is  more  likely  that  intestinal  and  gastric 
disturbances  may  occur  where  permanently  hard  waters  are  used. 

It  sometimes  happens  that  water  may  dissolve  poisonous  metals 
either  in  the  soil,  or  in  pipes  used  for  distributing  purposes,  and  so 
become  unwholesome.  Lead,  zinc,  and  iron  are  the  metals  most 
likely  to  occur  under  such  circumstances.  Where  water  is  acid,  as  in 
peaty  waters,  or  where  CO2  is  present  in  large  quantities,  the  solvent 
action  on  the  lead  is  much  increased.  In  such  districts  many  cases  of 
lead  poisoning  not  infrequently  occur,  although  all  waters  of  this  class 
are  not  necessarily  affected.  Zinc  is  much  less  liable  to  cause  trouble, 
although  where  water  is  in  contact  with  galvanized  pipes  an  appreci- 
able amount  of  zinc  may  often  be  determined.  When  iron  is  present 
in  waters  it  generally  comes  from  the  source  of  supply,  and  is  not 
derived  from  the  pipes  except  under  certain  circumstances.  Where 
present  in  the  proportion  of  0.5-1.0  part  per  million,  the  water  gener- 
ally has  an  objectionable  taste,  and  while  the  presence  of  this  metal  in 
small  quantities  is  not  attended  with  serious  results  on  health,  its  unde- 
sirable taste  and  appearance  is  against  its  use. 

The  danger  of  direct  absorption  of  poisons  from  water  is,  however, 
small  compared  with  that  attributable  to  the  influence  of  disease  organ- 
isms. Typhoid  fever  and  other  diseases  of  an  intestinal  character  not 


GENERAL   QUALITIES   OF  WATER. 

infrequently  find  their  way  into  water-supplies,  often  causing  widespread 
epidemics  of  these  infectious  maladies ;  but  this  subject  is  of  such  im- 
portance as  to  require  more  detailed  treatment  later  (Chapter  X). 

159.  Domestic  Use. — For  ordinary  domestic  use  the  quality  of  water 
must  be  such  that  it  can  be  used  in  cooking  and  for  laundry  use.      For 
these   purposes   water   should   not  contain   too  large  a  proportion   of 
mineral  ingredients.      Naturally,  the  same  sanitary  requirements  that 
are  necessary  in  drinking-water  also  obtain  in  water  used  for  culinary 
purposes.     Excessively  hard  waters  are  not  desirable,  as  the  flavor  of 
many  foods  is  considerably  impaired  when  cooked  in  the  same.      Iron- 
bearing  waters  are  also  unsuitable  for  this  purpose,  as  the  tannin  in  tea 
and  many  vegetables  produces  a  black  precipitate.      These  waters  are 
likewise  detrimental  for  laundry  use,  as  the  oxidation  of  the  ferrous  salts 
upon  exposure  to  the  air  produces  rust-spots  upon  clothes.    The  greatest 
difficulty  to  contend  with  in  the  laundry  in  the  case  of  ground-waters 
is  the  presence  of  soluble  salts  of  alkaline  earths,  such  as  lime  and 
magnesia.     When  soaps  are  added  to  such  ' '  hard  ' '  waters,  insoluble 
precipitates  are  produced,  and  it  is  therefore  necessary  to  use  a  much 
larger  quantity  of  soap  before  a  lather  can  be  produced.      One  part  of 
lime  carbonate  requires  about  eight  of  soap,  so  the  problem  from  an 
economic  standpoint  is  one  of  importance.      It  is  estimated  that  the 
city  of  Glasgow  saves  $180,000  annually  in  the  amount  of  soap  used 
since  the  introduction  of  the  soft  Loch  Katrine  water.* 

The  hardness  of  water  is  either  temporary  or  permanent,  depending 
upon  the  chemical  nature  of  the  dissolved  salts.  If  bicarbonates  are 
present,  the  CO2  contained  in  the  same  is  set  free  by  boiling,  in  which 
case  a  white  precipitate  consisting  of  carbonate  of  lime  is  formed.  As 
this  reduces  the  amount  of  lime  in  solution,  the  hardness  is  diminished, 
and  such  is  therefore  called  temporary,  in  contradistinction  to  the 
sulfates  and  chlorides  of  lime  and  salts  of  magnesia  that  are  not  so 
affected;  hence  waters  containing  these  salts  in  abundance  are  per- 
manently hard. 

160.  Manufacturing   Purposes. — For   different   manufacturing   pur- 
poses,  such  as  brewing,   sugar-making,    dyeing,   etc.,   the   quality  of 
water  is  subject  to  considerable  variation.      In  the  production  of  steam, 
trouble  is  experienced  with  all  waters  containing  an  excess  of  salts  of 
the  alkaline  earths  by  the  formation  of  boiler-scale.     With  the  tem- 
porarily hard  waters  a  friable  deposit  is  produced,  while  permanently 
hard  waters  cause  a  much  more  compact  ' '  scale, ' '  that  is  very  difficult 

*  Parkes,  Hygiene  and  Public  Health,  p.  10. 


152  QUALIl^Y  OF    WATER. 

to  remove.     The  accumulation  of  even  a  thin  layer  of  boiler  incrusta- 
tion involves  a  very  marked  loss  of  energy  in  the  coal  used. 

161.  Distribution  of  Bacteria  in  Soil. — To  understand  aright  the 
quality  of  waters  as  affected  by  germ-life  in  the  same,  it  is  necessary 
to  know  the  distribution  of  bacteria  in  the  soil.  Generally  the  rock- 
masses  are  covered  with  a  layer  of  more  or  less  finely  ground  material 
that  makes  up  the  soil.  This  layer  is  differentiated  into  two  strata: 
the  upper  one,  the  soil  proper,  that  is  darker  in  color  and  of  a  more 
porous  texture;  the  lower,  known  as  the  subsoil,  that  simply  represents 
the  unchanged  rock  debris.  As  the  soil  supports  abundant  vegetable 
and  animal  life  which,  as  it  dies,  is  resolved  into  decomposing  organic 
matter,  the  upper  layer  becomes  enriched  through  the  accumulation  of 
the  same  which  serves  as  future  plant-food.  The  organized  tissues  are 
first  disintegrated  by  the  action  of  the  saprophytic  bacteria,  as  noted  in 
the  changes  of  putrefaction  and  decay.  In  this  process  humus  is 
formed  and  the  looser  texture  and  darker  color  of  the  upper  soil-layer 
are  attributable  to  this  series  of  changes.  As  these  processes  are  con- 
trolled by  bacteria,  it  is  not  surprising  to  find  that  the  uppermost  soil- 
layers  are  teeming  with  myriads  of  these  forms,  often  millions  of  them 
being  present  in  every  gram.  This  number,  however,  diminishes 
rapidly  below  the  surface,  and  at  the  depth  of  two  or  three  yards  soils 
are  practically  sterile.  Cultivated,  but  more  particularly  inhabited 
soils,  have  a  higher  bacterial  content  than  virgin  forests  or  prairie  soils. 
The  character  and  texture  of  the  soil-layers  also  influence  to  some 
extent  the  distribution  of  these  micro-organisms.  The  reasons  for  this 
peculiar  distribution  lie  in  the  filtering  power  of  the  soil-particles  as  the 
moisture  percolates  downward ;  in  the  absence  of  organic  food-supplies 
in  the  deeper  layers ;  and  to  generally  unfavorable  growth  conditions 
(lower  temperature,  diminished  oxygen). 

Not  only  does  the  soil  harbor  all  kinds  of  bacteria  associated  with 
the  breaking  down  of  organic  matter,  but  the  formation  of  nitrates  from 
the  ammonia  so  produced,  due  to  the  nitrifying  bacteria,  also  occurs  in 
the  upper  layers  of  the  soil. 

It  is  at  once  evident  that  the  germ  content  of  any  water  that  comes 
in  contact  with  the  soil  must  be  profoundly  affected  by  the  soil-layers. 
So,  too,  with  the  air;  for  in  a  dried  condition,  the  fine  dust-like  particles 
with  their  adherent  organisms  are  readily  raised  by  wind-currents  from 
the  surface.  Of  course  by  far  the  majority  of  these  organisms  are  harm- 
less saprophytes ;  but  if  disease  matter  is  deposited  upon  the  surface  of 
the  soil,  there  is  often  nothing  to  prevent  the  distribution  of  pathogenic 
bacteria  in  quite  the  same  way. 


METEORIC    WATERS.  153 

While  the  germ  content  of  water  may  be  greatly  influenced  by  that 
of  the  soil,  it  must  be  remembered  that  the  flora  of  the  two  habitats 
are  not  necessarily  similar.  There  are  to  be  found  in  water  certain 
species  that  are  so  universally  present  that  they  may  be  called  water 
bacteria.  In  this  medium  they  are  able  to  grow  with  the  greatest  ease, 
even  in  waters  that  are  relatively  poor  in  inorganic  as  well  as  organic 
nourishment. 

METEORIC   WATERS. 

162.  Absorption  of  Impurities  from  Air. — Meteoric  waters  include 
the  various  forms  of  rainfall,  as  rain,  snow,  hail,  dew,  etc. ;  and  while 
they  are  not  normally  to  be  considered  as  immediate  or  direct  sources 
of  supply,  except  occasionally  for  individual  use,  yet  the  fact  that  they 
serve  as  indirect  sources  from  which  supplies  are  subsequently  drawn 
make  it  desirable  to  consider  their  quality.  As  watery  vapor  con- 
denses in  the  air  and  is  precipitated,  whether  in  the  form  of  rain  or 
snow,  it  absorbs  impurities  from  the  atmosphere.  Particles  of  dust  and 
dirt  are  washed  out  of  the  same,  and  in  the  neighborhood  of  large 
towns,  soot  and  other  combustion  products  may  pollute  these  waters 
to  a  very  considerable  degree.  The  gases  that  are  naturally  present 
in  the  air  are  also  more  or  less  readily  absorbed  by  water.  Not  only  is 
this  true  with  the  more  important  constituents,  N,  O,  and  CO2,  but 
such  substances  as  ammonia,  sulfuric  acid,  nitrous  and  nitric  acids  are 
generally  found.  Naturally  meteoric  waters  are  deficient  in  mineral 
matter  and  hence  are  soft.  Where  extremely  soft  their  action  on  lead 
pipes  is  severe. 

Water  in  falling  to  the  ground  in  the  form  of  either  rain  or  snow 
also  takes  up  germ-life  from  the  air.  Bacteria  and  spores  of  fungi  find 
their  way  into  it  in  considerable  numbers  from  the  subjacent  soil-layers, 
and  while  they  are  incapable  of  multiplication  in  the  air,  yet  in  a  dried 
condition  many  forms  can  retain  their  vitality  for  long  periods  of  time. 
The  result  is  that  either  rain  or  snow  catches  these  floating  forms  of 
life  and  so  they  are  carried  down.  Even  in  hailstones  they  are  to  be 
found  without  exception. 

Hill  *  records  some  observations  made  on  the  germ  content  of  the 
air  at  different  periods  during  a  rain-storm.  At  first  it  was  very  high, 
5495-5759  bacteria  per  c.c. ,  but  after  a  rain  of  12  hours  there  were  only 
15-57  germs.  The  number  of  organisms  in  the  air  decreases  rapidly 
with  an  increase  in  altitude.  On  mountain-sides  this  is  not  so  marked 
until  the  snow-line  is  reached. 

*  Public  Water-supplies,  p.  51. 


154  QUALITY  OF  WATER 

SURFACE-WATERS. 

163.  Character   Determined   by  Nature  of  Underlying  Soil.  —  As 
meteoric  waters  fall  to  the  earth,  a  portion  of  same  is  evaporated  into 
the  air,  while  the  remainder,  following  the  contour  of  the  surface,  either 
runs  off  or  percolates  into  the  underlying  soil.     That  which  is  apparent 
on  the  surface  of  the  soil  is  included  under  the  term  surface-waters, 
although  an  appreciable  part  of  such  supplies  has  been  subject  to  more 
or  less  percolation  through  soil  layers  (springs,  ground-water  drainage 
into  rivers).     Owing  to  the  fact  that  surface-waters  may  be  brought 
into  contact  with  mineral  and  organic  matter  that  renders  them  more 
or  less  impure,  the  quality  of  such  waters  is  subject  to  much  fluctuation. 
When  first  precipitated,  the  character  of  the  water  is  to  a  large  extent 
determined  by  the  nature  of  the  soil  over  which  it  flows  and  the  vege- 
table covering  of  the  soil,  but  in  river  systems  that  traverse  a  wide 
range   of    territory,  the   suspended   and   dissolved  impurities  are  not 
necessarily  related  to  the  character  of  the  land  drained. 

164.  Surface-Waters  as  Potable  Supplies.  —  As  organic  refuse,  either 
of  human,  animal,  or  vegetable  origin,  is  generally  found  on  the  surface 
of  soil,  it  is  evident  that  the  quality  of  surface-waters  is  often  impaired 
by  reason  of  pollution  with   such   material.     Inasmuch  as  the  most 
dangerous  refuse  of  this  character  is  that  connected  with  human  exist- 
ence, it  follows,  where  pollution  is  at  all  possible,  that  the  density  of 
population  will  exercise  a  potent  influence  on  the  character  of  such 
supplies.     For  this  reason  the  use  of  surface-waters,  particularly  those 
of  flowing  streams  in  densely  populated  watersheds,  is  a  menace  to  pub- 
lic health,  unless  they  are  first  subjected  to  some  adequate  method  of 
artificial  purification.     In   this   respect   lake-waters,  particularly   such 
enormous  reservoirs  as  our-  Great  Lakes,  are  naturally  of  much  better 
quality  than  running  waters  that  carry  off  the  surface-wash  and  drainage 
of  large  land-areas.     This  is  confirmed  by  the  typhoid  death-rates  of 
cities  using  this  water  in  comparison  with  those  furnished  with  river 
supplies.     In  1890-96  the  typhoid  deaths  for  the  five  largest  cities 
situated  on  the  Great  Lakes  averaged  42  per  100,000,  while  for  the 
five  largest  river  cities  of  the  United  States  it  was  58  per  100,000. 

A.   Flowing  Waters. 

165.  Naturally  the  availability  of  running  streams  as  sources  of 
municipal  water-supply  has  led  to  their  more  frequent  adoption  than 
any  other  kind  of  surface-water,  but  it  must  be  remembered  that  this  is 
not  because  they  are  of  better  quality.    Water  in  flowing  over  the  sur- 


S  URFA  CE-  WA  TERS.  155 

face  of  the  soil  naturally  acquires  numerous  impurities  that  it  would  not 
take  up  if  it  remained  quiescent.  These  substances  are  of  inorganic 
and  organic  origin,  each  class  being  represented  by  suspended  as  well 
as  dissolved  material.  One  character  of  flowing  waters  is  the  sudden 
change  in  composition  that  is  liable  to  occur  at  almost  any  time,  but 
more  particularly  during  flood  seasons.  By  reason  of  this,  a  supply 
that  is  generally  satisfactory  may  be  rendered  undesirable  in  a  short 
space  of  time.  Again,  not  only  are  running  streams  the  natural  drain- 
age-channels of  a  region,  but  they  must  to  a  large  extent  also  serve  as 
sewage-outlets  for  urban  populations  that  are  generally  increasing  in 
density. 

1 66.  Physical  Appearance. — Owing  to  the  fact  that  running  waters 
frequently  have  a  considerable  fall  per  mile,  thereby  producing  more 
or  less  rapid  currents,  it  naturally  follows  that  waters  of  this  class  in 
direct  contact  with  the  soil  erode  their  drainage-basins  with  consider- 
able rapidity  and  so  become  more  or  less  turbid. 

Babb  *  has  compiled  the  observations  made  on  various  rivers  as  to 
the  visible  load  of  sediment.  They  are  as  follows : 

Amount  of  Sediment  by  Weight. 

Potomac T  :  3575 

Mississippi i  :  1 500 

Rio  Grande i:    291 

Danube i  :  2880 

Nile i  :  2050 

Not  only  the  amount  but  the  nature  of  this  silt  varies  much  in 
different  streams,  depending  mainly  on  the  character  of  the  soil  and 
the  rate  of  flow.  Some  streams,  like  the  Missouri,  may  possess  a  very 
turbid  water,  but  the  size  of  suspended  particles  is  such  that  much  of 
this  sediment  is  deposited  when  the  water  is  quiescent;  other  streams, 
like  the  Mississippi  and  Ohio,  carry  a  smaller  load  of  silt,  but  the  fine 
colloidal  clay  that  is  so  abundant  in  the  same  makes  it  exceedingly 
difficult  to  clarify. 

Surface-waters  flowing  through  swampy  regions  are  usually  colored, 
due  mainly  to  the  extraction  of  soluble  coloring  matter  from  vegetable 
material.  Such  peaty  waters,  while  perhaps  unsightly  in  appearance, 
may  be,  however,  perfectly  wholesome  in  spite  of  this  physical  defect. 

While  flowing  surface-waters  do  not  dissolve  so  much  mineral 
matter  as  ground-waters,  yet  by  virtue  of  their  dissolved^ carbon  dioxide 
they  also  take  up  an  appreciable  amount,  depending  considerably  on 
the  character  of  the  soil  stratum  over  which  they  pass.  The  average 

*  Babb,  Science,  1893,  xxi.  p.  343. 


156  QUALITY  OF   WATER. 

of  a  large  number  of  European  and  American  rivers  shows  about  1 80 
parts  per  million  of  soluble  solids,  of  which  nearly  one-half  is  carbonate 
of  lime.* 

167.  Bacterial  Condition  of  Flowing  Streams. — Naturally  the  close 
contact  with  the  upper  soil-layers,  which  are  so  rich  in  micro-organisms, 
accounts  for  the  much  higher  germ  content  of  rivers  and  streams  than 
lakes.  It  might  be  thought  that  such  streams  would  show  a  larger 
number  of  bacteria  duing  a  low  stage  of  water  than  otherwise,  for  if  the 
sources  of  pollution  were  at  all  uniform,  the  lessened  summer  flow  would 
tend  to  concentrate  the  impurities.  As  a  fact,  however,  the  bacterial 
pollution  of  a  stream  is  always  greater  during  high-water  stages.  The 
more  rapid  rate  of  flow  increases  the  carrying  power  of  the  stream,  and 
much  more  suspended  matter,  as  silt  and  dirt,  is  borne  along  together 
with  the  bacteria  that  invariably  accompany  such  disturbance  of  the 
soil  particles.  Theobald  Smith  t  found  that  the  Potomac  River  water 
contained  the  following  number  of  bacteria  at  different  seasons : 

Dec.  Jan.  Feb.  March.  April.  May.  June.  July.  Aug.  Sept.  Oct.  Nov. 
967  3774.  2536  1210  1521  1064  348  255  254  178  75  116 

The  same  general  result  has  been  noted  by  Fuller  \  in  his  studies 
on  the  Ohio  River  at  Cincinnati  and  Louisville,  and  by  Frankland§  in 
the  case  of  the  Thames  and  Lea,  two  rivers  from  which  London 
derives  in  part  its  water-supply. 

According  to  Johnston  ||  the  bacterial  content  of  uninhabited  streams 
like  the  Saguenay  in  Canada  is  not  materially  different  from  that  of 
rivers  flowing  through  farming  regions,  although  where  a  stream  flows 
through  a  city  or  town  of  any  considerable  size,  especially  if  it  receives 
the  sewage  of  the  same,  the  amount  of  pollution  is  naturally  much 
increased.  Prausnitz  1  determined  the  following  data  for  the  Isar  River 
at  Munich. 

TABLE    NO.   23. 

BACTERIAL   CONTENT   OF    ISAR   RIVER. 

No.  of  Bacteria  per  c.c. 

Above  the  city  of  Munich 531 

150  feet  above  sewer  outfall 1.339 

Directly  opposite  sewer  outfall 121,861 

450  feet  below  sewer  outfall 33,459 

Ismaning  (8  miles  below  sewer  outfall) 9, m 

Freising  (20      "         "           "             "       2,378 

*  I.  C.  Russell,  Rivers  of  North  America,  p.  79. 
f  Med.  News,  April  9,  1887. 

\  Investigations  on  Purification  of  Ohio  River,  p.  34. 
§  Micro-organisms  in  Water,  p.  91. 
I  Hyg.  Rund.,  v.  p.  796. 
1"  Der  Einfluss  d.  Munch.  Canalisation,  1889. 


S  UK  FA  CE-  WA  TERS.  I  5  / 

Not  only  is  there  a  marked  increase  in  the  bacterial  content  of  the 
river,  but  it  is  also  evident  from  the  above  table  that  a  large  part  of 
this  pollution  is  lost  in  a  comparatively  short  time,  as  it  only  takes 
8  hours  for  the  current  to  reach  Freising,  20  miles  below.  These  con- 
ditions have  since  been  reinvestigated  (1898),*  and  it  has  been  found 
that  over  50  per  cent  of  the  bacteria  introduced  in  the  sewage  are 
eliminated  in  a  flow  of  twelve  miles. 

168.  Self-purification  of  Rivers. — This  process  of  spontaneous  puri- 
fication is  to  be  noted  in  all  streams  that  are  polluted  in  any  way  by 
the  introduction  of  sewage  or  soil  drainage.  Not  only  are  organic 
impurities  but  inorganic  as  well  eliminated  in  this  way.  The  rate  at 
which  this  process  goes  on  depends  upon  a  number  of  conditions,  such 
as  rate  of  flow,  character  of  bed  and  shores,  amount  of  sediment  carried 
in  water,  etc. 

Comparative  studies  (chemical  and  biological)  have  been  made  on 
a  number  of  important  streams  on  which  cities  are  situated.  Naturally 
most  of  the  data  yet  collected  are  on  European  waters. 

Stutzer  and  Knublauch  t  found  an  evident  purification  of  the  Rhine 
below  Cologne  in  2  miles'  flow.  Six  miles  below  the  bacterial  content 
on  the  left  shore  was  reduced  to  one-third.  On  the  right  shore  the 
diminution  was  less  rapid,  as  a  tributary  brought  into  the  stream  a 
large  amount  of  factory  waste  from  other  towns.  This  could  be  traced 
for  a  distance  of  16  miles  below  before  it  disappeared. 

Heider  \  traced  the  pollution  of  the  Danube  below  Vienna  for  2  5 
miles,  a  distance  covered  in  a  flow  of  8-9  hours.  In  this  stream  the 
sewage  of  the  city  was  diluted  from  225-880  times.  Schlatter§  in 
1889  observed  the  effect  of  the  sewage  of  Zurich  for  6  miles,  and 
recently  Thomann,  ||  in  investigating  the  same  problem  ten  years  later 
to  determine  if  the  zone  of  pollution  had  been  materially  increased, 
found  only  one  case  at  the  distance  of  9  miles  where  the  germ  content 
was  approximately  as  low  as  it  was  above  the  city.  At  this  distance 
the  average  germ  content  was  about  50  per  cent  higher  than  before  the 
introduction  of  the  sewage.  During  this  period  the  city  had  increased 
its  population  about  50  per  cent,  so  the  zone  of  pollution  was  propor- 
tionally increased.  The  same  result  was  observed  at  Munich  in  study- 
ing the  Isar,  as  is  indicated  in  Table  No.  24. If 

*  Hyg.  Rund.,  1898,  vm.  p.  161. 

f  Cent.  f.  allg.  Gesundheitspflege,  1893,  abs.  in  Hyg.  Rund.t  IV.  p.  225. 
\  Oest.  Sanitatswesen,  1893,  No.  31. 
%Zeit.f.  Hyg.,  IX.  p.  56. 
||  Ibid.,  XXXHI.  p.  i. 
^f  Hyg.  Rund.,  1898,  vm.  p.  161. 


IS8 


QUALITY  0<F   WATER. 
TABLE  NO.  24. 

BACTERIAL    CONTENT   OF   RIVER   ISAR    BELOW   MUNICH. 


Year. 

Name  of  Observer. 

Number  of  Bacteria  per  c.c. 

Oberftihring, 
3  Miles. 

Ismaning, 
8  Miles. 

Freising, 
21  Miles. 

Landshut, 
45  Miles. 

1889 
1890 

1893 
1895-6 

Prausnitz 

G.,  L.,  P.,N.* 
Deichstetter, 
Willemar 

6,824 
2,960 
15,065 

14,185 

3,608 
1,510 
7,134 

7,893 

9IO 

1,976 

2,900 

3.140 
24,100 

)  

A  few  American  streams  have  been  more  or  less  perfectly  studied 
in  this  regard.  In  the  sanitary  survey  made  in  Ohio  of  the  more 
important  streams,  the  same  general  relations  were  noted.  Bleilet 
found  in  every  case  a  marked  difference  between  the  bacterial  content 
of  water  above  and  below  the  various  cities,  but  this  marked  increase 
always  dropped  again  to  normal  in  the  course  of  a  flow  of  a  number  of 
miles,  providing  there  was  no  new  source  of  pollution.  In  a  general 
way  the  bacteriological  fluctuations  correspond  to  the  variation  in  the 
free  and  albuminoid  ammonia,  but  in  some  cases  increase  in  ammonias 
was  due  to  influx  of  vegetable  impurities,  in  which  instance  of  course 
the  bacterial  increase  was  not  as  marked  as  after  addition  of  organic 
matter  of  animal  origin. 

The  sanitary  survey  made  on  the  Mohawk  and  Hudson  rivers, 
New  York,  show  a  similar  relation.  The  numerical  increase  in  bacteria 
in  river-water  occasioned  by  the  introduction  of  the  sewage  of  Albany 
remained  evident  for  a  distance  of  about  1 1  miles  below  the  city.J 

By  far  the  most  extensive  study  that  has  yet  been  made  on  Ameri- 
can streams  is  that  carried  on  by  Jordan  §  on  the  Illinois  River  in 
connection  with  the  Chicago  Drainage  Canal.  The  waters  of  this  stream 
were  studied  chemically  and  bacteriologically  both  before  and  after  the 
opening  of  the  Sanitary  Canal,  in  order  to  determine  whether  the  intro- 
duction of  the  sewage  of  the  city  of  Chicago  would  exert  any  deleterious 
influence  on  the  quality  of  the  St.  Louis  water-supply  drawn  from  the 
Mississippi.  The  appended  data  show  the  purification  observed  in 
Illinois  River  under  normal  conditions. 

*  Gold schmidt,  Luxcmburger,  Frans,  Hans  u.  Ludwig,  Neumeyer,  Prausnitz. 

t  Examination  of  Sources  of  Ohio  Public  Water-supplies,  p.  137. 

J  Rei u.  N.  Y.  State  Board  of  Health,  1892,  p.  526. 

§  Jordan,  Bacterial  Self-Purification  of  Streams,  Jo.  Expt.  Med.  v.:  271,  1900. 


SELF-PURIFICATION  OF  STREAMS. 


'59 


TABLE   NO.  25. 

CHLORINE  AND  BACTERIAL  DETERMINATIONS  MADE  ON  WATER  IN  ILLINOIS  RIVER 
AND  ITS  TRIBUTARIES  UNDER  AUSPICES  OF  CHICAGO  SANITARY  DRAINAGE  COM- 
MISSION. 


Collecting  Stations 

Distance 
from  Bridge- 
port in  Miles. 

Chlorine, 
Parts  per 
1,000,000. 

Bacteria  per  c.c. 

Number  of 
Analyses 
Made. 

O 
29 

II9.2 
II7.4 
7-9 
104.8 

3-4 
68.1 

58-5 
5-0 

61.2 

46.1 
44-2 
40.9 
40.  i 

38-4 
36-2 

4-5 
29-3 
22.9 
18.3 

2.8 

1,245,000 
650,000 
9,180 
486,000 
5,000 
439,000 
27,400 
6,510 
7,970 
16,300 

11,200 

3,660 

758,000 
492,600 
16,800 
5,080 
14  ooo 
4,800 

10,200 
7,6OO 

19 

30 
28 
28 
28 
26 
26 
29 
30 
31 
29 
30 
22 

29 
26 
21 
26 

19 
28 
29 

33 

57 
81 

La  Salle     

95 
123 

159 
165  • 
175 
199 

Sangamon  River  at  Chandlerville 

231 

288 
3i8 

The  extent  of  natural  purification  of  the  Illinois  River  can  be 
observed  from  the  above  table.  The  steady  diminution  in  the  amount 
of  chlorine  is  noteworthy  all  the  way  from  Bridgeport,  where  a  large 
proportion  of  the  sewage  of  Chicago  is  present,  to  Grafton,  where  the 
Illinois  joins  the  Mississippi.  The  bacterial  reduction  is  also  continuous 
for  a  distance  of  over  160  miles,  until  the  river  receives  at  Wesley  City 
the  large  amount  of  refuse  from  Peoria.  It  is  to  be  noted  that  this 
large  additional  load  of  pollution  does  not  increase  the  chlorine  so  much 
as  it  does  the  bacteria,  but  this  is  probably  due  to  the  fact  that  the 
sewage  contains  a  very  large  amount  of  manufacturing  wastes  (distillery 
and  glucose  refuse). 

The  table  also  includes  the  tests  made  on  tributary  streams,  and  it 
is  strikingly  noticeable  that  in  no  case  but  one  is  the  chlorine  content 
of  such  a  nature  as  to  add  materially  to  the  pollution  of  the  main  river. 

169.  Causes  of  Self-purification  of  Streams. — The  explanation  of  the 
cause  of  this  phenomenon  is  so  complex  that  no  single  principle  can 
be  cited  that  will  apply  to  all  cases.  The  different  factors  that  are 
operative  under  changing  conditions  may  be  grouped  under  two  heads : 


QUALITY   OF    WATER 

(1)  Factors  concerned  in  apparent  purification,  as  dilution  and 

sedimentation. 

(2)  Factors  concerned  in  actual  destruction  of  bacteria,  as  sun- 

light, vital  concurrence,  unsuitable  food-supply. 
Polluted  waters  may  have  their  germ  content  reduced  per  unit  of 
volume  by  the  first  class  of  factors  without  necessarily  destroying  the 
bacteria  associated  with  the  polluting  material. 

170.  Dilution.  — In  a  purely  mechanical  manner,  polluted  material 
is  greatly  diluted  when  discharged  into  a  running  stream.      This  dilu- 
tion varies  'greatly  with  the  varying  amount  of  sewage  discharged  and 
the   stage   of  water   in   the   stream.      In  rapidly  flowing  streams   this 
factor  is  more  potent  than  in  sluggish  rivers.      Although  a  stream  may 
not  receive  any  material  additions  by  way  of  tributaries,  yet  the  volume 
of  water  in  a   river  is  constantly  being  augmented  by  the  influx   of 
ground-water  that  drains  into  the  drainage-channels  from  the  surround- 
ing land,  and  so  the  extent  of  dilution  is  being  gradually  increased. 

171.  Sedimentation. — Removal  of  bacteria  by  sedimentation  may 
occur  in  two  ways.      There  may  be  a  gradual  settling  of  the  organisms 
themselves  by  virtue  of  their  specific  gravity,  or  they  may  be  entangled 
and  carried  down  by  the  subsidence  of  suspended  particles  of  silt.    The 
latter  method  is  by  far  the  most  effective,  and  in  streams  is  the  only 
way  in  which  sedimentation  exerts  any  influence.      Subsidence  of  sus- 
pended matter  begins  to  occur  whenever  the  current  is  lessened,  due 
either  to  expansion  of  stream  or  diminished  fall  per  mile.      The  Spree 
below    Berlin    illustrates    the    influence    of   diminished    flow.*     From 
190,000  bacteria  per  cc.  found  in  the  river  as  it  emptied  into  the  Havel, 
an  expansion  of  the  stream  7  miles  broad,  the  number  fell  to  9000  as 
it  issued  from  this  natural  sedimentation  basin. 

A-  peculiar  case  of  sedimentation  has  been  noted  by  Van't  Hoff,  t 
and  is  utilized  in  securing  the  water-supply  of  Rotterdam  from  the 
Maas  (Rhine).  This  city  is  on  tide- water,  and  at  flood-tide  the 
checking  of  the  current  as  it  meets  the  sea  is  so  marked  that  the 
bacterial  content  of  the  river  is  lessened  about  50  per  cent.  During 
this  period  of  partial  subsidence  the  necessary  supply  is  largely 
secured. 

In  removing  the  bacteria  from  a  flowing  stream  by  sedimentation, 
the  organisms  are  not  necessarily  destroyed.  They  may  be  carried  to 
the  bottom  by  the  precipitation  of  the  inorganic  matter  and  in  the 
slimy  ooze  of  the  river-bed  find  conditions  more  or  less  suitable  for  de- 

*  Frank,  Zeit.  f.  Hyg.,  in.  p.  355. 
f  Cent.  f.  Bakt.,  XVIII.  p.  265. 


SUNLIGHT.  j^! 

velopment.  No  data  have  yet  been  collected  on  this  phase  of  the 
subject,  but  Russell  found  in  studying  the  bacterial  flora  of  the  sea- 
bottom  (Atlantic  and  Mediterranean)  *  that  the  germ  content  was  much 
greater  than  that  of  the  water,  and  to  a  considerable  extent  was  made 
up  of  species  not  found  in  the  water  above.  This  would  indicate  that 
the  high  content  of  the  mud  is  not  entirely  due  to  sedimentation. 

172.  Sunlight. — Direct  sunlight  has  a  potent  germicidal  effect  on 
many  bacteria,  and  Buchner  t  has  ascribed  a  prominent  part  to  this 
factor  in  explaining  the  phenomena  of  self-purification  of  waters. 
Experimental  work  has  conclusively  demonstrated  that  the  germicidal 
effect  is  caused  by  the  chemical  and  not  the  heat  rays  of  the  spectrum. 
Not  only  do  the  direct  rays  of  sunlight  destroy  the  bacteria,  but  even 
diffused  light  in  some  cases  exerts  a  prejudicial  influence. 

Care  must,  however,  be  taken  in  interpreting  these  data,  which  have 
been  secured  for  the  most  part  in  experiments  carried  on  in  various 
culture  media ;  for  it  has  been  determined  that  such  media  in  the  pres- 
ence of  direct  sunlight  and  air  may  decompose,  and  antiseptic  substances 
as  peroxide  of  hydrogen,  be  formed. 

Some  observers,  however,  as  Frankland,  \  have  carried  on  their 
investigations  in  natural  waters  as  well  as  in  culture  media;  and  have 
found,  for  instance,  that  anthrax  spores  are  for  the  most  part  quickly 
killed  in  such  waters,  although  other  species  retain  their  vitality  for 
months ;  but  they  are  destroyed  less  rapidly  in  water  than  in  culture 
media. 

The  data  collected  as  to  the  depth  to  which  this  disinfecting  action 
of  the  light  is  effective  are  very  contradictory.  Buchner  §  found  that 
the  germicidal  influence  of  the  light  was  very  marked  when  cultures 
were  submerged  at  the  depth  of  4  to  5  feet,  and  demonstrable  with 
typhoid  in  agar  at  10  feet;  but  Arloing,  ||  Frankland,  1  and  Procacci** 
have  all  found  that  an  appreciable  depth  of  water  (a  few  inches  to  a 
foot  or  so)  materially  diminished  the  disinfecting  action.  The  action 
is  probably  considerably  less  in  rivers  than  in  lakes  owing  to  the  in- 
creased turbidity  of  flowing  streams. 

Buchner'stt  observations  on  the  increase  in  bacteria  in  lake  waters 

*  Zeit.f.  Hyg.,  xi.  p.  165. 

f  Cent.  f.  Bakt.,  1892,  xil.  p.  217. 

\  Proc.  Roy.  Soc.,  1893,  LIU.  p.  316. 

§  Cent.  f.  Bakt.,  1892,  xi.  p.  781;  also  xil.  p.  217. 

(I  Arch,  de  Physiol.y  1886,  VII.  p.  209. 

1"  Proc.  Roy.  Soc.,  1893,  LIU.  p.  204. 

**  Annali  d.  Inst.  d'  Igiene  Sper.  di  Roma,  1893,  III.  p.  437. 

ft  Tiemann-Gartner,  Das  Wasser,  p.  579. 


1 62  QUALITY  OF   WATER. 

during  the  night  when  compared  with  observations  made  at  sundown 
are  sometimes  cited  as  confirmatory  evidence  of  this  disinfecting  action, 
but  there  are  too  many  disturbing  factors  that  might  enter  in  to  mask 
the  real  effect  to  rely  entirely  on  observations  to  prove  this  point. 
Indeed  the  observations  by  Prausnitz  and  others  on  the  same  river 
(Isar)  showed  that  while  frequently  a  marked  decrease  was  noted  in 
sunny  days,  they  also  observed  the  same  on  days  in  which  the  sky  was 
completely  overcast. 

From  the  data  already  at  hand  it  seems  quite  clear  that  the  disin- 
fecting action  of  direct  light  has  been  considerably  overestimated. 
While  it  is  unquestionably  operative  to  some  extent,  it  plays  at  most 
only  a  subordinate  role. 

173.  Vital  Concurrence.  —  Water    contains   so   many   other   living 
forms  than  bacteria  that  it  would  be  surprising  'if  there  were  not  a 
strong  competition  between  the  various  forms  of  life  represented  in  the 
same.     Different  observers  have  ascribed  to  green  plant-forms  (water- 
weeds,  algae,  diatoms,  etc.)  a-  purifying  power,  but  the  evidence  as  to 
their  effect  in  a  polluted  stream  is  far  from  conclusive.     It  is  true  that 
these  chlorophyll-bearing  organisms  do  not  subsist  directly  on  organic 
matter,  and  in    some   cases,   as   Schenck    has    noted,   where   polluted 
streams  are  readily  purified,  organisms  of  this  class  are  not  at  all  abun- 
dant ;  hence  their  purifying  action  is  by  no  means  satisfactorily  proven. 

The  distinctively  dangerous  disease  organism  in  water,  i.e.,  the 
typhoid  bacillus,  is  apparently  affected  by  the  presence  of  other  bac- 
terial forms  in  abundance.  Jordan,  Russell  and  Zeit  *  have  shown  that 
the  typhoid  disappears  much  more  rapidly  in  a  polluted  than  an  unpol- 
luted water,  and  Russell  and  Fuller  f  have  determined  that  this  disap- 
pearance is  closely  associated  with  intimate  contact  with  sewage  forms 
of  bacteria.  Whether  this  is  due  to  by-products  toxic  to  the  disease 
organism  or  not  is  difficult  to  prove,  but  Frost  has  shown  a  distinct 
antagonism  between  the  typhoid  organism  and  several  saprophytic  forms. 

This  same  condition  is  doubtless  true  with  reference  to  the  disap- 
pearance of  B.  Colt  in  flowing  streams.  Weston  noted  at  New  Orleans 
the  nearly  complete  disappearance  of  B.  Coli  in  the  water  of  the  Missis- 
sippi River,  although  heavily  charged  with  silt  and  extensively  polluted. 
For  a  considerable  distance  above  the  city,  no  surface  pollution  is  added 
owing  to  the  level  system.  Consequently  spontaneous  purification  of 
polluted  water  became  operative. 

174.  Unsuitable  Food-supply.  —  The  sewage  bacteria,  and  to  some 

*  Jour.  Inf.  Diseases,  1904,  I.,  p.  641.          t  Ibid.,  Sup.  No.  2,  Feb.,  1906. 


AERATION.  .         163 

extent  the  soil  organisms,  do  not  find  favorable  conditions  for  rapid 
growth  in  ordinary  waters.  This  is  evident  from  the  numerous  experi- 
ments that  have  been  made  to  determine  the  viability  of  such  organisms 
as  the  typhoid,  cholera,  and  colon  forms  (222).  When  these  alone 
are  added  to  water  or  in  competition  with  other  forms,  they  rapidly 
diminish  in  numbers.  Still  the  evidence  of  pollution  sometimes  dis- 
appears in  a  flow  of  6  to  8  hours,  and  in  such  cases  it  could  hardly 
be  due  to  their  having  been  killed.  In  cases  of  retarded  purification, 
as  the  Seine  in  France,  where  pollution  is  still  recognizable  after  two 
to  four  days'  flow,  this  factor  might  be  more  effective. 

175.  Aeration. — It  is  a  popular  belief  that  aeration  greatly  improves 
the   character  of  water,   but  numerous   experiments   on   the   effect   of 
oxygen  and  motion,  singly  and  in  conjunction  with  each  other,  fail  to 
show   any   material   effect.       Leeds    failed    to    find    any   difference    in 
Niagara  water  above  and  below  the  falls.      The  experiments  by  Mills 
on  artificial  aeration  also  show  but  little  effect. 

176.  Chemical  Reaction. — Certain  chemical  combinations  may  take 
place  in  water  that  will  tend  to  purify  the  same.     The  Schuylkill  above 
Philadelphia  is  heavily  charged  with  iron,  salts,  and  acids  (due  to  mine- 
drainage),  but  in  flowing  over  a  limestone  reigon  the  acids  in  the  water 
neutralize  the  lime  salts,  precipitating  much  of  the  lime  and  iron,  mak- 
ing a  soft  and  wholesome  water  from  what  was  originally  unfit  for  use. 

177.  Conclusion. — That  flowing  streams  polluted   or  contaminated 
in  any  way  do  undergo  a  spontaneous  purification  there  can  be  no  ques- 
tion.     The  factors  that  have  been  considered   above  probably  account 
for  the  most  of  such  change,  although  the  effect  of  each  operative  factor 
varies  in  different  cases  owing  to  the  change  in  conditions. 

Naturally  no  hard-and-fast  rule  can  be  given  that  will  apply  to  all 
conditions,  but  the  most  definite  conclusions  that  can  be  drawn  from 
the  data  already  at  hand  indicate  that  sedimentation  and  dilution  play 
the  more  important  role  in  the  purification  of  waters.  Undoubtedly 
sunlight  and  the  action  of  other  living  forms  are  also  operative  to  some 
extent,  but  the  results  already  obtained  lead  to  the  belief  that  these  are 
only  of  subordinate  influence,  especially  in  the  case  of  streams. 

The  important  problems  for  the  engineer  are :  How  soon  does  this 
purification  take  place?  Can  streams  once  polluted  be  used  again  with 
safety  ? 

From  available  data  it  seems  evident  that  a  stream  once  polluted 
with  any  considerable  amount  of  sewage  is  unsafe  to  use  for  a  water- 
supply  so  long  as  there  is  any  trace  whatever  of  pollution  remaining. 
It  is  impossible  to  set  a  distance  limit,  or  even  a  time  limit  of  flow 


1 64 


QUALITY  OF  WATER. 


(although  this  would  be  less  objectionable),  for  such  limits  would  vary 
much  in  each  instance.  It  has  been  claimed  in  England  that  no  stream 
is  sufficiently  purified  by  the  time  it  reaches  the  sea  to  warrant  its  use, 
and  it  is  well  established  that  typhoid  epidemics  have  been  distributed 
for  scores  of  miles  down-stream.  Just  how  long  disease  bacteria  can 
retain  their  vitality  in  water  has  long  been  a  disputed  matter,  but  as 
long  as  a  stream  shows  any  evidence  of  pollution  it  certainly  should  be 
regarded  as  dangerous. 

B.  Impounded  Surface-waters  (Lakes,  Ponds,  Reservoirs}. 

178.  The  waters  of  an  open  expanse,  such  as  a  lake,  are  less  likely 
to  show  marked  pollution  than  flowing  streams,  because  in  relatively 
quiescent  waters,  solid  matter,  excepting  the  finest  clays,  cannot  long 
remain  in  suspension  and  the  factor  of  land  contamination  is  of  less 
prominence.  In  large  bodies  of  water,  as  the  Great  Lakes,  the  effect 
of  pollution  is  limited  to  shore  regions,  but  under  certain  conditions 
may  be  considerably  extended,  as  is  to  be  noted  along  the  south  shore 
of  Lake  Superior,  where  the  water  is  frequently  rendered  densely  turbid 
for  a  distance  of  6-10  miles  from  shore  because  of  a  stratum  of  tena- 
cious red  clay  along  the  coast-line. 

At  certain  seasons  of  the  year,  the  water-supplies  of  towns  along 
this  shore,  relying  on  lake-water,  are  greatly  impaired.  The  follow- 
ing data  collected  by  the  writer  at  Duluth-Superior  show  the  germ 
content  of  the  polluted  shore-line  in  comparison  with  the  crystal-clear 
lake-water. 

TABLE   NO.  26. 

NUMBER    OF    BACTERIA    PER    C.C.    IN    LAKE   SUPERIOR   AT    DULUTH-SUPERIOR. 


Depth  at  which  Sample  was  secured. 

Distance  from  Land  at  which  Sample  was  secured. 

Shore. 

ii  Miles. 

5  Miles. 

5  Miles. 

10  Miles. 

2457* 

87 

23 

AC  feet 

44 
50 

C-l         " 

16 

6O      "                           

II 

20 

5 

8O      "         

6 
100  feet 
clear 

Depth    of    water  at   different 
stations         

3  feet 
very  turbid 

60  feet 
cloudy 

80  feet 
turbid 

90  feet 
faintly  turbid 

Appearance  of  water  at  sur- 

*  Average  of  14  different  samples. 


VERTICAL    CIRCULATION  IN  LAKES.  165 

179.  Vertical  Circulation  in  Lakes.* — Owing  to  the  fact  that  the 
maximum    density   of  water   is    somewhat   above  the    freezing-point 
(39. 2°  F.,  4°  C.),   water  in  lakes  is  more  or   less  subject  to  vertical 
currents  that  cause  the  upper  and  lower  layers  to  mix  under  certain 
temperature  conditions.      In  large  lakes  of  the  temperate  type  there 
is  generally  no  circulation  of  the  water,  as  the  heavier  cold  water  rests 
on  the  bottom.      In  smaller,  shallower  lakes  there  are  periods  of  stag- 
nation,   in   which   there  is   no  vertical    circulation.      These    occur  in 
winter  and  summer.      Between  these  periods  there  is  an   "overturn- 
ing," i.e.,  a  vertical  circulation  due  to  temperature  changes.      In  the 
spring,   as    the    surface    warms    above    the  freezing-point,    the    water 
increases  in  density  and  therefore  becomes  heavier.     This  causes  it  to 
sink,  thus  producing  vertical  currents.      In  the  fall  the  surface  cools 
and  the  water  is  apt  to  be  stirred  by  wind  action  until  the  warmer, 
lighter  bottom  water  is  forced  to  rise  as  the  colder  surface-water  sinks. 

In  shallow  lakes,  small  reservoirs,  etc.,  the  circulation  of  the  water 
is  going  on  at  all  times,  except  while  the  surface  is  frozen ;  but  where 
reservoirs  are  20  feet  deep  or  so,  the  phenomenon  of  stagnation  may 
at  times  occur. 

This  is  a  matter  of  some  importance,  as  the  temperature  of  a  supply 
is  affected  by  these  changes.  Moreover,  if  water  is  drawn  from  a  low 
level  in  the  reservoir,  it  may  be  derived  from  layers  that  have  been 
stagnant  for  considerable  periods  of  time. 

180.  Bacterial  Content  of  Open  Surface-waters. — The  improvement 
in  physical  appearance  of  lake-waters  in  comparison  with  rivers  reflects 
itself  at  once  in  the  biological  and  chemical  character  of  the  same. 
Generally  speaking,  waters  of  this  class  contain  far  less  bacteria  than 
do  running  streams.     While  of  course  there  is  no  marked  uniformity  in 
numbers,  yet  it  is  rare  that  waters  of  this  type  contain  more  than  a  few 
hundred  organisms  or  at  most  more  than  a  few  thousand  bacteria  per 
c.c. ;  and  these  for  the  most  part  are  harmless  water  saprophytes. 

These  organisms  are  more  or  less  uniformly  distributed  throughout 
the  entire  mass  of  the  water;  but  according  to  Nicholson's t  studies 
made  on  Lake  Mendota  under  the  writer's  direction,  the  lower  strata 
are  considerably  richer  in  germ-life  than  the  intermediate  layers.  The 
surface  frequently  contains  more  organisms  due  to' the  effect  of  dust. 

In  summer  this  bacterial  distribution  is  apt  to  be  obscured  through 
the  action  of  wind,  light,  variation  in  temperature,  etc.,  but  in  winter, 
when  the  water  is  covered  with  a  mantle  of  ice  and  these  disturbing 

*  See  Chapter  V  in  Whipple's  Microscopy  of  Drinking-water, 
f  Thesis,  Univ.  of  Wis.,  1900. 


1 66  QUALITY   OF    WATER. 

conditions  are  more  or  less  thoroughly  eliminated,  this  zonary  distribu- 
tion is  rendered  more  apparent.  In  the  mud  or  slime  that  collects  on 
the  bottom  of  lakes  and  ponds,  the  bacterial  content  is  greatly 
increased. 

Where  surface-waters  sustain  a  copious  growth  of  algae,  as  is  very 
frequently  the  case,  the  bacterial  content  of  the  water  during  this  state 
may  be  rendered  abnormal  through  the  development  of  organisms 
living  on  the  organic  matter  that  is  derived  from  the  death  of  the  vege- 
table organisms. 

181.  Natural   Purification   Processes. — The   marked    diminution    in 
germ  content  of  lake-water  as  distance  from  shore  increases  indicates 
that  the  natural  purification  of  quiescent  surface-waters  is  also  as  marked 
as  is  that  of  flowing  streams.      Except  in  the  case  of  inflow  of  streams 
of  considerable  size,  the  evidence  of  land-pollution  does  not  extend  far. 
The  reason  for  this  is,  in  the  main,  dilution  and  sedimentation.     The 
disappearance  of  perceptible  currents  causes  suspended  matter  to  settle 
quickly,  thereby  reducing  greatly  the  germ  content.      These  organisms 
may  be  able  to  retain  their  vitality  in  the  ooze  for  some  time,  but  the 
larger  proportion  found  in  the  lake  mud  are  forms  that  have  evidently 
developed  in  this  habitat  (171).  • 

Lortet*  even  claims  to  have  found  a  number  of  pathogenic  bacteria 
at  the  depth  of  120-150  feet  in  the  mud  of  Lake  Geneva,  Switzerland. 
The  ooze  formed  from  the  deposition  of  sediment  in  water  gradually 
becomes  more  and  more  compacted,  and,  owing  to  the  formation  of 
ferrous  sulfide,  a  black  gelatinous  precipitate  is  produced  that  cements 
the  particles  into  a  semi-solid  sticky  mass.  Fuller  has  noted  the  forma- 
tion of  this  material  in  the  artificial  subsidence  reservoirs  at  Cincinnati,  t 

Direct  sunlight  is  undoubtedly  effective  as  a  factor  in  purifying 
waters  of  this  class,  for  quiescent  waters  are  as  a  rule  clearer,  and 
therefore  the  actinic  rays  would  be  able  to  penetrate  more  deeply 
than  in  turbid  flowing  waters. 

182.  Influence  of  Vegetation. — The  quality  of  surface-waters  is  some- 
times affected  by  the  copious  development  of  vegetable  life.      This  is 
particularly  apt  to  occur  in  relatively  shallow  lakes  where  the  growth 
of  "water- weeds,"  as  Myriophyllum,   Chara,   Vallisneria,  Ranunculis, 
etc.,  may  be  so  rank  as  to  accumulate  organic  matter  in  large  quanti- 
ties.    While  these  plant-forms  have  no  direct  relation  to  disease  pro- 
duction, yet  the  decay  of  this  vegetable  material  may  seriously  affect 
the  quality  of  such  water. 

*  Cent  /.  Bakt.,  1891,  ix.  p.  709. 

f  Kept,  on  Cincinnati  Water  Purification,  p.  120. 


ODORS  IN    WATER-SUPPLIES.  l6/ 

183.  Odors  in  Water-supplies. — It  used  to  be  thought  that  the  pres- 
ence of  any  appreciable  odor  in  water  was  due  entirely  to  the  natural 
processes  of  decay,  but  in  addition  to  these  it  is  now  known  that  a 
number  of  living  organisms,  both  plant  and  animal,  give  off  odors 
during  their  development,  due  to  the  presence  of  oils  formed  in  the 
cells.  Oils  of  different  sorts  can  be  detected  by  the  sense  of  taste  in 
extremely  dilute  solutions.  According  to  Whipple*  the  odor  of 
peppermint  can  be  noted  in  water  containing  I  part  of  oil  to  50,000,000 
parts  of  water ;  clove-oil,  I  to  8,000,000;  cod-liver  oil,  I  to  1,000,000. 
This  explains  why  the  odor  from  a  relatively  small  number  of  some  of 
these  odoriferous  organisms  is  so  manifest.  There  are  a  number  of 
plant  and  animal  forms  that  appear  so  frequently  in  ponds  and  reser- 
voirs of  water-supplies  as  to  warrant  specific  mention.  Besides  these 
there  is  a  much  larger  number  of  other  species  that  occur  less  fre- 
quently. 

Of  the  aromatic  odors  formed,  that  produced  by  the  diatom, 
Asterionella,  is  perhaps  the  strongest,  t  Where  only  a  few  of  these 
organisms  are  present  the  odor  is  aromatic ;  where  more  abundant  it 
recalls  a  geranium  odor;  and  where  very  numerous  a  distinct  fishy 
odor  is  apparent.  Whipple  has  found  by  experiment  that  50,000  cells 
of  A  sterionella  would  produce  enough  oil  so  that  the  dilution  was  only 
I  :  2,000,000,  an  amount  that  is  quite  within  the  range  of  detection. 
Other  diatoms  are  not  infrequently  found,  but  their  odoriferous  proper- 
ties are  less  pronounced. 

Grassy  odors  are  caused  mainly  by  the  blue-green  algae,  the 
Cyanophycece.  The  most  distinctive  member  of  this  group  is  Anabcena^ 
When  abundant,  the  water  has  a  taste  resembling  green  corn.  Vege- 
table odors  are  caused  by  the  diatoms,  Synedra  and  Melosira.  With 
the  former,  5000  cells  per  c.c.  suffice  to  produce  a  distinct  odor. 
Whipple  has  often  found  in  the  Brooklyn  supply  as  many  as  15,000- 
20,000  of  these  organisms  per  c.c. 

Of  all  defects  of  this  class  in  water,  fishy  odors  are  the  most  objec- 
tionable. One  of  the  animal  forms  belonging  to  the  protozoa,  Uro- 
glena,  produces  an  odor  resembling  cod-liver  oil;  while  another, 
Synura,  recalls  the  odor  of  ripe  cucumbers.  Troubles  of  this  character 
have  appeared  several  times  in  the  Boston  water-supply.  At  first  they 
were  ascribed  to  Spongilla,  the  fresh- water  sponge,  but  later  they  were 
traced  to  Synura,  which  was  found  to  be  developing  in  large  numbers 
in  Lake  Cochituate  under  the  ice. 

*  Microscopy  of  Drinking-waters,  p.  123. 
f  1.  c.,  p.  125. 


168  QUALITY  OF   WATER. 

It  might  naturally  be  thought  that  these  troubles,  being  due  in  the 
main  to  vegetable  growth,  would  be  more  apt  to  prevail  during  the 
summer  months  than  at  other  seasons,  but  such  is  not  necessarily  the 
case.*  Of  the  algae,  Anabcena  is  apt  to  occur  most  frequently  from 
July  to  September.  Pediastrum,  Raphidium,  Scenedesmus,  Closterium, 
and  Staurastrum  are  most  numerous  in  July  and  August,  but  the 
diatoms,  as  Asterionella,  Melosira,  Synedra,  and  Tabellaria,  are  often 
more  abundant  in  early  spring  or  late  fall  than  at  other  seasons.  The 
protozoan  forms  (Dinobryon,  Peridinium,  and  Trachelomonas)  occur 
most  commonly  in  March,  July,  and  August. 

Troubles  from  bad  or  unpleasant  odors  in  water-supplies  are  very 
much  more  apt  to  occur  in  open  surface-waters  than  any  other;  hence 
impounded  supplies  may  develop  these  abnormal  conditions  at  times. 
Of  71  supplies  examined  by  the  Massachusetts  Board  of  Health,  a  bad 
taste  was  noted  in  45,  and  of  these  two-thirds  gave  serious  trouble. 

The  introduction  of  the  copper  sulfate  treatment  has  done  much  to 
make  it  possible  to  overcome  the  production  of  undesirable  odors  due 
to  algae,  but  this  method  should  be  used  with  caution.  For  further 
discussion  see  Art.  569. 

C.   Ice  Supplies. 

184.  Influence  of  Freezing  on  Bacterial  Life. — The  quality  of  ice  is 
dependent  primarily  upon  the  character  of  the  water  before  it  is  frozen. 
It  is  true  that  some  of  the  grosser  solid  impurities  are  expelled  from 
water,  especially  if  congelation  takes  place  gradually,  but  it  does  not 
follow  that  ice  made  from  polluted  water  is  safe  for  human  use. 

Not  only  does  the  examination  of  ice  show  that  it  is  generally 
poorer  in  germ-life  than  the  subjacent  water  beneath,  but  experimental 
tests  on  the  resistance  of  bacteria  to  freezing  indicate  that  many  forms 
and  more  particularly  disease  species  are  capable  of  retaining  their 
vitality  for  many  months. 

Prudden,t  Sedgwick,|  and  Park  §  have  found  that  the  typhoid 
bacillus  is  capable  of  retaining  its  vitality  for  at  least  three  months 
when  frozen,  although  there  was  a  rapid  diminution  in  number  of 
organisms  immediately  after  freezing. 

In  the  process  of  freezing  from  60-90  per  cent  of  the  contained 
organisms  are  killed,  although  many  vegetative  as  well  as  spore-bear- 

*  Parker,  Mass.  Bd.  Health,  Exam,  of  Waters,  1890,  p.  597. 

\  Med.  J?ec.t  March  26,  1887. 

\  Science,  March  23,  1900. 

§  Journ.  of  Boston  Soc.  Med.  Sc.t  April,  1900. 


SUBTERRANEAN    WATERS.  169 

ing  forms  are  able  to  resist  freezing  for  a  while  at  least.  While  from 
experimental  work  it  has  been  definitely  shown  that  typhoid  and  other 
pathogenic  organisms  are  able  to  retain  their  vitality  for  long  periods 
of  time  when  frozen,  still  there  is  no  authenticated  case  in  which 
typhoid  epidemics  have  been  traced  to  the  use  of  impure  ice,  although 
intestinal  disturbances  are  known  to  have  been  caused  in  this  way.* 

SUBTERRANEAN   WATERS. 

185.  Change  in  Quality  Due  to  Percolation. — That  portion  of  the 
rainfall  that  finds  its  way  into  the  soil  is  rapidly  changed  in  quality  by 
percolation  through  the  various  soil-layers.  As  it  flows  through  the 
soil  toward  the  ground-water  level  it  loses  the  larger  portion  of  the 
impurities  derived  from  the  air  and  the  soil  surface,  but  at  the  same 
time  it  absorbs  other  substances  from  the  layers  through  which  it 
passes,  so  that  in  general,  the  quality  of  subterranean  waters  is 
materially  different  from  those  of  surface  origin. 

To  some  extent  the  gaseous  content  of  rain-water  is  changed  as  it 
courses  through  the  soil.  The  particles  of  suspended  matter  (soot, 
dust,  and  germ -life)  that  are  absorbed  from  the  air,  together  with  the 
organic  matter  and  bacteria  derived  from  the  upper  soil-layers,  are 
readily  removed  in  the  percolation  process,  so  that  at  a  depth  of  a  few 
yards  at  most  the  germ-life  of  the  surface  of  the  soil  and  all  its  attend- 
ant impurities  have  been  eliminated. 

On  the  other  hand  the  percolating  water  dissolves  certain  inorganic 
elements,  and  especially  by  virtue  of  the  CO2 ,  which  it  has  absorbed 
from  the  air,  this  solvent  action  is  greatly  increased. t  In  this  way  the 
salts  of  lime  and  magnesia  are  rendered  soluble,  making  hard  waters, 
while  other  mineral  elements,  such  as  the  silicates,  are  also  carried  more 
readily  into  solution.  This  action  increases  materially  the  total  solids 
of  a  water,  more  particularly  those  of  an  inorganic  character.  Subter- 
ranean waters  therefore  carry  a  load  of  soluble  solids,  while  the  solids 
of  surface-waters  are  more  largely  in  suspension.  In  regions  rich  in 
humus  the  ground-water  may  contain  a  large  amount  of  organic  as  well 
as  inorganic  constituents. 

Not  infrequently  such  waters  may  also  contain  ferrous  salts.  In 
the  presence  of  humus  and  absence  of  oxygen,  the  sulfates  may  be 
reduced  to  hydrogen  sulfide,  and  the  nitrogen  compounds  to  ammonia. 
These  iron-containing  ground-waters  are  of  not  infrequent  occurrence ; 

*  Sedgwick,  Science,  March  23,  1900. 

f  Pure  water  dissolves  about  I  part  in  10,800  of  carbonate  of  lime,  while  the  same 
saturated  with  carbon  dioxide  is  able  to  render  soluble  about  I  to  1000. 


I/O  QUALITY   OF    WATER. 

and  in  many  cases  they  are  otherwise  desirable,  but  the  presence  of  the 
iron  impairs  the  quality  of  a  supply  for  drinking  and  domestic  use,  not 
so  much  on  hygienic  grounds  as  because  of  its  physical  appearance. 
Moreover,  in  such  waters,  the  so-called  iron  fungus,  CrenotJirix  poly- 
spora,  is  very  apt  to  become  established,  in  which  case  the  iron  is 
oxidized  from  a  ferrous  to  a  ferric  form.  Inasmuch  as  this  organism 
does  not  require  light  for  its  growth,  it  is  able  to  grow  in  covered 
reservoirs  and  pipes. 

186.  Purification  of  Water  in  the  Soil. — By  the  operation  of  natural 
processes  in  the  soil,  water  is  purified  in  passing  from  the  surface  to 
the  ground-water  level.      The   forces   concerned   in    this    change   are 
physical,  chemical,  and  biological.      The  larger  part  of  the  suspended 
matter  is  removed  by  filtration  in  a  purely  mechanical  manner.     There 
is  also  an  attraction  for  substances  in  solution,  as  is  evident  from  the 
fact  that  the  color  of  water  due  to  dissolved  matter  is  removed  in  part 
at  least  by  percolation  through  soil. 

Chemical  changes  may  also  be  caused  by  the  action  of  one  sub- 
stance or  another,  precipitating  or  dissolving  the  same,  but  the  most 
effective  transformations  are  those  th?t  are  induced  by  biological 
causes,  viz.,  the  micro-organisms  present  in  the  soil-layers.  In  the 
upper  layers,  organic  matter,  vegetable  or  animal,  undergoes  fermen- 
tation, putrefaction,  or  decay,  with  the  result  that  the  nitrogenous 
organic  substances  are  gradually  converted  into  soluble  condition, 
generally  ammonia  compounds.  The  carbonaceous  elements  are 
changed  into  carbon  dioxide,  water,  and  organic  acids. 

When  material  containing  nitrogen  has  been  converted  into 
ammonia  compounds,  it  is  then  acted  on  by  the  nitrifying  bacteria, 
forming  first  nitrites  and  then  nitrates. 

These  mineralizing  processes,  which  are  really  oxidation  changes, 
take  place  more  rapidly  in  the  superficial  layers  of  the  soil,  where 
oxygen  is  more  abundant.  Temperature  and  character  of  the  soil  also 
exert  an  influence  on  rate  of  change. 

In  swampy  regions  containing  a  large  amount  of  humus,  and  there- 
fore so  acid  as  to  inhibit  the  development  of  the  nitrate-producing 
bacteria,  the  nitrogenous  material  accumulates  as  ammonia  products 
rather  than  as  nitrates. 

187.  Capacity  of  Soil  for  Purification. — The  purifying  action  of  the 
soil   is   not   unlimited,   and  under  certain   artificial  conditions   largely 
ceases  to  be  operative.      Naturally,  the  action  of  any  pollution  is  inter- 
mittent, the  offensive  material  being  discharged  on  the  surface  at  inter- 
vals, between  which  the  natural  purifying  forces  are  operative.     This 


SUBTERRANEAN    WATERS.  I? I 

condition  is  essential  to  adequate  purification.  Under  artificial  condi- 
tions occasioned  by  man's  presence,  this  intermittent  action  may  be 
suspended.  If,  therefore,  sewage  is  discharged  continuously  on  to  the 
surface  of  the  soil,  even  though  in  small  amounts,  the  action  of  the 
natural  purifying  processes  is  disturbed,  and  the  result  is  that  the  soil 
becomes  saturated  with  organic  matter  which  is  not  converted  into  the 
harmless  substances  that  would  naturally  be  produced  as  a  result  of 
the  operation  of  soil  processes.  It  is  in  this  way  that  the  soil  of  thickly 
populated  areas  like  cities  loses  its  property  of  spontaneous  purification, 
often  to  such  an  extent  that  the  ground-water  is  rendered  impure. 
Under  such  conditions,  while  the  organisms  of  disease  may  be  held 
back  by  the  soil  layers,  the  soluble  products  of  organic  decay  are  able 
to  percolate  into  the  ground,  thus  making  it  especially  difficult  to 
determine  the  wholesomeness  of  such  water  where  reliance  is  placed 
on  chemical  examination  alone. 

188.  Extent  of  Filtration  Necessary  to  Effect  Purification. — The  dis- 
tance through  which  the  water  must  pass  before  it  is  sufficiently  purified 
for  potable  purposes  is  a  question  of  very  considerable  importance. 
Judging  from  the  higher  typhoid  mortality  rates  of  populations  using 
shallow  wells  in  comparison  with  those  utilizing  a  supply  from  a  deeper 
source,  it  is  evident  that  efficient  purification  is  often  not  reached  in 
shallow  wells.  This  may  of  course  be  due  in  some  cases  to  direct 
pollution.  Not  infrequently  it  may  happen,  where  the  ground-water  is 
subject  to  considerable  oscillations  in  level,  that  at  high  stages  this 
generally  sterile  water  layer  comes  in  contact  with  soil  that  is  not  bac- 
teria-free. This  condition  might  possibly  arise  in  cities,  especially 
where  the  land  has  been  filled  in,  and  where  decomposing  organic 
matter  is  some  distance  below  the  soil  surface. 

The  depth  necessary  to  insure  efficient  purification  will  also  vary 
with  the  filtering  power  of  the  soil.  Loose,  sandy,  or  gravelly  soil  hav- 
ing larger  pore-spaces  will  permit  of  more  ready  filtration  than  compact 
clay  loams.  Pfuhl  *  has  determined,  by  adding  a  culture  of  some  easily 
demonstrable  organism  like  B.  prodigiosus  to  water  in  a  well,  that 
there  can  be  a  lateral  movement  into  the  ground  for  10  feet  or  more. 

Again  there  is  to  be  mentioned  the  possibility  of  direct  rifts  or 
channels  existing  in  the  soil  or  rock.  Holes  made  by  animals  (rats 
and  larger  rodents),  earthworms,  Crustacea,  etc.,  frequently  permit  of 
direct  passage  of  unfiltered  water  to  considerable  depths.  A  number 
of  cases  of  wells  and  springs  have  been  recorded  where  the  germ  con- 
tent was  so  high  and  of  such  a  character  as  to  leave  no  doubt  but  that 

*  Pfuhl,  Zfit.f.  Hyg,,  xxv.  p.  549. 


1/2  QUALITY  OF   WATER. 

there  was  a  direct  connection  with  the  surface.*  Generally  this  con- 
dition is  more  likely  to  'prevail  along  faulting  cracks  in  rock  layers 
than  in  soil,  or  in  limestone  regions  where  subterranean  channels  have 
been  dissolved  by  the  water.  The  classical  case  of  the  Lausanne, 
Switzerland,  epidemic, t  where  the  village  well  was  infected  from  a 
polluted  brook  over  a  mile  distant,  but  which  had  an  underground 
connection  with  the  well,  is  a  striking  illustration  of  the  unreliability 
of  natural  purification  through  soil  layers.  Gaff ky  J  showed  that  the 
Wittenberg  typhoid  epidemic  in  1882  was  due  to  infection  of  an  open 
well  from  vaults  50  feet  distant.  The  stratum  in  this  case  was  gravel. 

Thoinot  and  Brouardel  §  traced  a  typhoid  epidemic  in  Havre  to 
pollution  through  80  feet  of  chalk  to  a  clay  substratum  where  the  water 
appeared  as  a  spring.  Such  cases  happily,  however,  are  exceptional. 
In  general,  ground-water  supplies  are  the  most  reliable  of  any.  For 
individual  use  and  for  small  municipalities,  they  will  always  remain  the 
principal  source  of  supply,  and  their  use  could  undoubtedly  be  extended 
in  some  cases  to  larger  cities. 

189.  Spring- waters. — In  the  popular  mind  springs  are  supposed  to 
represent  the  purest  of  supplies,  but  under  certain  circumstances  this 
type  of  ground-water  may  not  be  wholly  pure.  They  are  produced  by 
percolating  rain-water  flowing  along  an  impervious  stratum  until  it  finds 
an  outcrop  to  the  surface.  Often  in  mountainous  districts  the  depth 
and  thoroughness  of  percolation  over  and  through  rock  masses  is  so 
limited  that  the  water  may  not  equal  in  purity  the  normal  ground- 
water.  Generally,  spring-waters  before  exposure  to  surface  of  soil 
are  relatively  deficient  in  micro-organisms,  as  they  represent  filtered 
waters,  but  as  they  appear  at  the  surface,  the  water  comes  again  in 
contact  with  organic  matter  and  soil  bacteria,  and  may  thus  receive  a 
considerable  quota  of  organisms  from  this  source,  although  generally 
the  germ  content  of  unpolluted  springs  is  below  100-200  per  c.c.  || 

While  spring-water  usually  has  a  low  initial  bacterial  content,  the 
organisms  contained  in  such  waters  possess  the  property  of  very  rapid 
multiplication  during  storage.  According  to  Miquel  If  this  rapid  but 
transitory  power  of  development  characterizes  the  bacteria  of  spring- 
waters  in  contradistinction  to  the  slower  and  more  persistent  growth 
that  occurs  in  impure  waters. 

*  Tiemann-Gartner,  Das  Wasser,  p.  523. 

f  Deutsch.  Arch.  f.  Klin.  Med,,  1893,  Bd.  II. 

\  Gaffky,  Mitt.  a.  d.  Kais.  Gesundheitsamte,  1884,  n.  p.  413. 

§  Thoinot,  Bacteriology,  p.  62;  also  Ann.  Past.,  1889,  in.  p.  145. 

\  Tiemann-Gartner,  Das  Wasser,  p.  492. 

T  Manuel  pratique  d'Analyse  bact.  d.  Eaux,  1891,  p.  146. 


SUBTERRANEAN   WATERS.  1 73 

190.  Well-waters. — It  not  infrequently  happens  that  there  maybe 
several  impervious  geological  layers  superimposed  on  each  other  that 
serve  to  collect  the  water  from  different  areas.  Under  such  circum- 
stances the  upper  stratum  will  retain  the  local  ground-water  of  the 
region,  while  the  more  copious  supply  beneath  is  the  result  of  percola- 
tion from  a  larger  and  perhaps  distant  source.  Shallow  wells  often 
strike  only  the  surface  ground- water,  which  is  sometimes  of  poor  quality, 
while  the  water  of  deep  wells  which  tap  the  larger,  more  universal 
supply  in  the  rock  is  usually  more  thoroughly  purified.  Shallow  wells 
dug  in  the  soil  and  walled  up  dry  are  often  to  be  found  in  the  more 
crowded  portions  of  cities.  Generally  these  are  sunk  in  soil  that  is 
more  or  less  thoroughly  impregnated  with  organic  refuse,  so  that  the 
water  in  the  same  is  often  in  a  polluted  condition,  not  having  been 
purified  by  its  passage  through  a  shallow,  and  at  the  same  time  con- 
taminated, soil  stratum. 

Then,  again,  wells  of  this  character  practically  serve  as  drainage- 
basins  for  the  thickly  populated  areas  above  them,  and  when  walled  up 
dry,  seepage  from  the  soil  is  carried  directly  into  the  same.  The 
influence  of  near-by  closets  and  vaults  is  thus  not  infrequently  to  be 
observed.  Cesspools  are  particularly  dangerous,  because  they  contain 
so  much  water  which  must  find  its  way  into  the  soil  by  percolation. 
Just  how  far  wells  of  this  character  should  be  placed  with  reference  to 
vaults  and  cesspools  depends  upon  the  character  of  the  soil  and  the 
contour  of  the  surface.  In  shallow  wells  where  the  ground-water 
layer  may  be  lowered  through  pumping,  the  zone  of  influence  may  be 
considerably  widened.  Pfuhl  places  the  average  distance  at  100  feet, 
but  it  is  evident  that  no  exact  limit  can  be  drawn.  Where  the  ground- 
water  lies  near  the  surface  the  distance  should  be  manifestly  increased 
to  a  maximum  limit.  Not  infrequently  open  wells  of  this  class  may 
be  polluted  directly  from  the  surface,  unless  graded  up  so  as  to  carry 
off  the  local  drainage.  Wells  of  such  character  frequently  serve  as 
disseminators  of  water-borne  diseases.  Their  condition  is  at  once 
betrayed  by  a  chemical  or  bacterial  test.  They  contain  large  numbers 
of  bacteria,  and  the  presence  of  gas-producing,  indol-forming  organisms 
at  once  indicates  their  impure  condition.  Such  wells  generally  have  a 
high  chlorine  content,  as  this  element  continues  to  increase  with  the 
growth  of  population,  and  the  presence  of  nitrogen  in  nitrous  and  nitric 
forms  and  considerable  quantity  of  the  ammonias  is  further  proof  of 
pollution  with  organic  refuse. 

The  better  class  of  wells  that  are  sunk  into  the  permanent  ground- 
water  are  either  drilled  or  driven.      In  these  the  sides  of  the  wells  are 


174  QUALITY  OF   WATER. 

made  impervious  to  seepage  by  iron  casing,  so,  that  barring  pollution 
from  direct  surface-drainage  at  the  top,  the  only  ordinary  chance  for 
contamination  is  in  tapping  an  impure  ground-water. 

191.  Bacterial  Content  of  Wells. — While  the  ground-water  is  pre- 
sumably free  from  bacteria,  or  at  least  very  nearly  so,  water  as  it  is 
taken  from  wells  almost  always  has  an  appreciable  germ  content.  In 
the  case  of  shallow,  dug  wells  where  opportunity  for  infection  from 
above  or  seepage  from  sides  is  present,  and  where  the  temperature  of 
the  considerable  mass  of  water  is  such  as  to  permit  more  rapid  bacterial 
growth,  it  is  not  at  all  uncommon  to  find  thousands  of  organisms 
per  c.c.  The  infiltration  of  organic  matter  aids  materially  in  the 
development  of  this  germ  life. 

In  the  better  type  of  wells,  drilled  or  driven,  the  germ  content  is 
subject  to  wide  variation.  Normally  where  all  opportunity  for  external 
pollution  is  excluded,  the  number  of  bacteria  per  c.c.  is  very  small. 
Frankland  found  in  some  of  the  deep  wells  in  the  chalk  in  England 
only  six  bacteria  per  c.c.,  but  often  where  the  most  careful  precautions 
are  taken  in  securing  samples  a  much  larger  number  is  to  be  found. 
Sedgwick  and  Prescott  *  found  the  following  numbers  in  a  series  of  deep 
wells  in  Massachusetts  examined  by  them : 

No.  of  Bacteria  per  c.c. 

Well  ioo  feet  deep 30 

Well  193     "       "     269,    254 

Well  213     "       "     101,     106 

Well  254     "       "     150,    135 

Well377     "       " 48,      54 

Well  454     "       " 205,     214 

These  waters  were  characterized  by  the  absence  of  liquefying  bac- 
teria and  the  abundance  of  pigment-forming  species.  Similar  results 
have  also  frequently  been  recorded  by  others.  The  following  summary 
from  Tiemann-Gartner's  book  on  Water  t  gives  an  idea  of  average 

conditions. 

TABLE   NO.  27. 

SUMMARY    OF   OBSERVATIONS    ON    BACTERIAL    CONTENT    OF    WELLS. 
Locality  Observed.  Observer.  No.  per  c.c. 

(  34  wells  in  64  had  less  than  ioo 
Mayence Egger 


I  53 

Stettin Link                     27  "  "47 

Steinberg Rastall                  9  "  "   10 

Kaiserslautern Bokorny             59  "  "  78 

Leitmeritz Maschek             12  "  "  59 


Gotha Becker 


(34 
\  50 


53 
53 


Kiel Fischer  51     "       "  179  " 

HOchst Grandhomme  108     "       "  118  " 

*26  Rept.  Mass.  Bd.  of  Health,  1894,  p.  435. 
f  Das  Wasser,  p.  489. 


500 


ioo 
500 
ioo 

500 


SUBTERRANEAN    WATERS.  1/5 

It  is  evident  from  the  above  that  while  the  average  conditions  in 
well-water  do  not  show  a  high  germ  content,  yet  even  good  wells  often 
contain  a  considerable  number  of  bacteria. 

Of  course  it  at  times  happens  that  even  deep  wells  may  receive 
ground- water  that  has  not  been  wholly  purified.  Pfuhl*  cites  an 
instance  where  pollution  occurred  after  passing  through  180  feet  of 
gravel,  but  these  cases  must  be  exceptional.  From  whence  do  these 
organisms  then  come  ?  In  all  probability  infection  occurs  at  the  time 
of  digging  the  well.  The  machinery  used  in  the  digging  is  far  from 
being  bacteriologically  clean,  and  in  this  way  the  water  is  seeded  from 
the  beginning.  Many  of  the  species  are  able  to  grow  even  in  pure 
water,  and  the  result  is  that  some  development  occurs,  so  that  various 
forms  persist  in  the  water.  The  following  observations  made  by  Hast- 
ings and  the  writer  on  newly  drilled  wells  where  chance  for  contami- 
nation was  absolutely  excluded  point  to  this  conclusion : 

WELL    NO.    I    DRILLED    IIO   FEET   IN    DRIFT   (GRAVEL,    SAND,    ETC.),    JULY,    1899. 

Number  of  bacteria  per  c.c.  July      24,  1899 10,080 

Oct.         6,  1899 2,050 

Dec.      14    1899 380 

March  29,  1900 18 

WELL   NO.    2    DRILLED   60   FEET    IN    SAME    FORMATION,    NOV.,    1899. 

Number  of  bacteria  per  c.c.  Dec.      14,  1899 n,45o 

March  29,  1900 570 

Both  of  these  wells  contained  an  enormous  number  of  liquefying 
bacteria  at  the  beginning,  but  non-liquefying  species  predominated 
later. 

Frankel  t  has  also  demonstrated  that  this  infection  occurs  from 
without  by  disinfecting  a  well  with  a  mixture  of  carbolic  and  sulfuric 
acid ;  then  by  removing  the  chemicals  by  long-continued  pumping. 
Wells  so  treated  remained  germ-free  for  6-7  days,  but  ultimately 
became  invaded  from  above. 

192.  Effect  of  Pumping. — Bacterial  growth  can  go  on  at  surprisingly 
low  temperatures;  and  in  deep  wells  in  the  ground  where  the  water  is 
in  the  neighborhood  of  48-50°  F.,  the  conditions  are  such  that  multi- 
plication of  germ-life  readily  occurs.  When  a  considerable  volume  of 
water  is  present  in  the  well,  the  distribution  of  bacterial  life  throughout 
the  same  can  readily  occur.  Under  such  circumstances  the  number  of 
organisms  per  c.c.  in  the  water  can  often  be  greatly  reduced  by  pump- 
ing out  the  standing  water  and  allowing  fresh  quantities  of  germ-free 
ground- water  to  percolate  into  the  reservoir.  Even  with  long-con - 

*  Arch.  f.  offentl.  Gesundheitspflege  in  Elsass-Loth.,  1895,  xvi.  Heft  2. 
\Zeit.f.  ffyg.t\i.  p.  23. 


1/6  QUALITY  OF   WATER. 

tinued  pumping  it  is  practically  impossible  to  remove  all  bacteria 
adherent  to  the  sides  of  well  and  pump.  Maschek  records  an  instance 
where  31,500  gallons  of  water  were  pumped  from  a  well  in  12  hours, 
and  the  germ  content  was  reduced  from  2750  to  1064;  in  another  case 
it  fell  from  458  to  68  when  1600  gallons  were  removed. 

Gruber  *  carried  on  uninterrupted  pumping  experiments  on  a  well 
for  several  days  with  the  following  results : 

Beginning  of  test several  thousand  per  c.c. 

8  days'  pumping 472       " 

14     '•  " 22       '• 

75     "  "        10      " 

193.  Effect  of  Organic  Nutriment  on  Growth  of  Water  Bacteria. — The 

ability  of  bacteria  to  thrive  in  well-waters  depends  in  large  degree  on 
the  amount  of  nutriment  they  find  in  such  a  habitat.  Rubner  \  added 
to  a  well  a  small  quantity  of  meat  extract  and  then  determined  its 
effect  on  germ-life.  A  quantity  that  was  only  able  to  increase  the 
amount  of  oxygen  consumed  by  1-2  mg.  caused  the  germ  content  to 
rise  from  10,000  to  50,000  and  finally  to  170,000,  at  approximately 
which  point  it  remained  for  some  weeks.  This  indicates  that  if  a  well 
is  so  poorly  constructed  as  to  permit  of  the  percolation  of  soluble  organic 
matter,  the  conditions  are  such  as  would  favor  growth  of  organisms  in 
the  same. 

194.  Artesian  Wells, — In  flowing  wells  where  the  flow  is  always 
outward  it  would  be  difficult   to  imagine  how  infection  from  outside 
might  occur,  and  yet  a  bacteriological  examination  of  such  waters  not 
infrequently  reveals  the    fact   that   they  may  contain   some  bacteria, 
although  generally  much  less  than  ordinary  wells.      Such  a  condition 
would  naturally  seem  at  variance  with  the  idea  that  the  ground-water 
is  practically  sterile ;  but  when  one  recalls  that  in  a  number  of  these 
deep  subterranean  supplies  Crustacea  and  small  fish  %  have  been  found 
in  some  cases,   it  is  evident  that  a  deep  supply  does  not  necessarily 
mean  that  the  water  has  really  been  filtered  through  a  very  deep  layer 
of  soil  or  rock.     Russell  found  at  Dubuque,  la.,  in  several  artesian 
wells  over   1500  ft.  deep  from  30-90  organisms  in  one,  and  300-400 
in  another.      Several  analyses  were  made  of  these  waters  at  different 
times  with  corroborative  results. 

It  often  happens  that  water  from  deep  wells  and  springs  contains 

*  Deutsche  Vierteljahrschr.  f.  offentl.  Gesundheitspflege,  XXV.  p.  415. 
f  Arch.  f.  Hyg.,  xi.  p.  365. 

%  In  the  artesian  wells,  180  feet  deep,  situated  at  Biskra  in  the  Sahara  desert, 
mollusks  and  small  fish  are  found  at  times. 


EFFECT  OF  STORAGE.  1 77 

nitrites  in  quantities  that  would  be  sufficient  to  condemn  a  water  if  it 
was  from  a  shallow  well  or  a  surface-water.  This  condition  may, 
however,  have  no  significance,  as  it  may  be  brought  about  by  a  reduc- 
tion by  various  causes  of  the  nitrates  in  the  deeper  layers  of  the  soil. 

EFFECT    OF   STORAGE    AND    DISTRIBUTION    ON    QUALITY. 

195.  Improvement  of  Water  by  Storage, — In  most  cases  in  municipal 
supplies  it  is  necessary  to  store  the  water  in  reservoirs  of  varying  size, 
so  as  to  provide   against  contingencies.      Under  such  conditions  the 
water  is  sometimes  subject  to  changes,  some  of  which  improve  while 
others  impair  the  quality  of  the  supply. 

The  changes  that  result  in  an  improved  condition  occur  generally 
with  waters  of  surface  origin  rather  than  with  spring-  or  ground-waters. 
In  the  storage  of  waters  of  this  class  sedimentation  is  effective  in 
eliminating  much  of  the  suspended  matter,  including  living  organisms, 
as  well  as  a  portion  of  the  dissolved  organic  matter.  Where  consider- 
able mineral  matter  is  in  suspension,  as  in  many  rivers,  especially  during 
flood  seasons,  the  degree  of  purification  by  subsidence  is  even  greater 
than  where  the  suspended  solids  are  less.  St.  Louis  derives  its  supply 
from  the  Missouri  River,  which  at  some  seasons  of  the  year  may  contain 
nearly  2  per  cent  by  volume  of  suspended  solids.  Nearly  95  per  cent 
of  this  is  precipitated  in  the  storage-reservoirs  during  24  hours,  with  the 
result  that  the  germ  content  is  greatly  reduced. 

The  factors  operative  in  the  spontaneous  purification  of  lakes  are 
also  of  value  in  the  changes  induced  by  storage  in  reservoirs. 

The  color  of  waters,  especially  when  due  to  organic  matter,  is 
lessened  by  storage,  although  this  bleaching  action  of  the  sun's  rays 
does  not  extend  rapidly  to  any  great  depth. 

196,  Impairment  of  Water  by  Storage. — Surface-waters,   however, 
may  be  impaired  in  quality  by  storage  under  certain  conditions.     A 
marked  effect  is  apt  to  arise  from  the  stagnation  of  the  water.     Under 
certain  temperature  conditions,   the  water  in   large  reservoirs  during 
quiescent  periods  *  does  not  circulate  vertically  and  therefore  the  lower 
layers   become   stagnant.      If  the  bottom  of  such  reservoirs   contains 
considerable  organic  matter,  as  is  generally  the  case  where  water  is 
impounded   in   artificially  made  lakes,   then  the   dissolved  oxygen   is 
rapidly  exhausted,  causing  the  death  of  all  organisms  incapable  of  lead- 
ing an  anaerobic  existence.     Such  waters  frequently  acquire  bad  odors. 
The  following  observations  by  Whipplet  show  this  variation. 

*  This  is  especially  liable  to  occur  when  reservoirs  are  covered  with  ice.  (Drown, 
24  Mass.  Bd.  Health,  1892,  p.  333.) 

f  Whipple.     Microscopy  of  Drinking-water,  p.  137. 


QUALITY  OF   WATER. 
TABLE    NO.  28. 

DISSOLVED   OXYGEN    IN   LAKE   COCHITUATE,    MASS. 

Per  cent  of  Saturation. 
Aug.  16,  '91.    Sept.  28,  '91 

Surface 79  90 

10  feet  deep 84  81 

20  "   "  30  33 

40  "   "  20  8 

50  "   "  : o     o 

If  the  organic  matter  in  the  upper  soil  layers  is  removed  before 
impounding  these  surface-waters,  this  difficulty  does  not  occur,  a  con- 
dition that  generally  obtains  in  lakes  that  have  a  gravelly  or  sandy 
bottom. 

Ground-waters  and  those  which  have  been  purified  by  artificial  filtra- 
tion are  not  improved  by, storage  in  open  reservoirs.  In  fact  waters 
that  have  been  thus  purified  by  filtration  through  soil-layers  and  the 
germ  content  thereby  greatly  reduced  are  much  more  liable  to  deterio- 
rate than  grow  better  by  storage.*  A  supply  that  is  drawn  from  both 
ground  and  surface  sources,  as  in  the  Brooklyn  supply,  is  much  more 
apt  to  give  trouble  than  a  pure  ground-water,  as  the  admixture  of  sur- 
face-water will  generally  seed  the  water  with  living  organisms,  which 
are  able  to  develop  rapidly  in  such  waters. 

When  purified  waters  are  allowed  to  stand,  the  bacteria  are  able  to 
develop  prolifically;  and  while  this  development  has  no  special  signifi- 
cance from  a  sanitary  standpoint,  because  these  organisms  are  generally 
the  normal  water  bacteria,  still  it  does  not  improve  the  water  in  any 
Way. 

Ground-waters,  owing  to  their  passage  through  the  soil,  contain 
considerable  soluble  mineral  matter,  and  therefore  such  waters  are  well 
adapted  to  the  development  of  some  kinds  of  plant-life.  Whipplet 
thinks  this  is  less  likely  to  happen  in  a  new  reservoir  than  in  one  which 
has  been  long  in  use.  The  accumulation  of  organic  sediment  on  the 
bottom  of  the  reservoir  is  very  apt  to  facilitate  the  development  of  this 
type  of  microscopic  life  (183),  of  which  the  diatom,  Asterionella,  is 
perhaps  the  most  undesirable  representative  on  account  of  the  marked 
odor  that  it  produces.  Waters  of  surface  origin  that  have  been  filtered 
act  in  this  respect  like  a  ground-supply. 

This  development  of  algae  can  be  prevented  by  cohering  the  reser- 
voirs, as  direct  sunlight  is  necessary  for  the  multiplication  of  these  green 


*  Water-supply  of  Brookline,  Mass.,  19  Kept.  Mass.  Bd.  Health,  p.  89, 
f  Microscopy  of  Drinking  Water,  p.  141. 


EFFECT  OF  DISTRIBUTION  ON  QUALITY.  179 

plant-forms  *  or  by  the  application  of  the  copper  sulfate  treatment  (569). 
In  large  reservoirs  this  latter  method  is  naturally  most  feasible,  but  it 
should  be  used  with  circumspection.  The  death  of  certain  species  often 
permits  of  the  growth  of  other  forms. 

In  covered  reservoirs,  however,  certain  ground-waters  may  also  be 
affected.  Fungi,  bacteria,  and  animal  forms,  living  as  they  do  on 
organic  material,  do  not  need  sunlight.  Hence  they  might  find  in 
covered  reservoirs  a  favorable  habitat,  but  as  animals  generally  live  on 
algae,  their  presence  is  determined  by  this  fact.  The  most  important 
organism  of  this  class  is  Crenothrix,  the  iron  bacterium,  which  often 
grows  so  luxuriantly  in  waters  containing  iron  and  organic  matter  as 
frequently  to  clog  the  service-pipes  by  the  accumulation  of  vegetable 
growth.  Sometimes  this  water-pest  flourishes  to  such  an  extent  as  to 
necessitate  a  change  in  base  of  supply,  as  in  Berlin,  or  the  introduction 
of  a  method  of  treatment  that  will  eliminate  the  iron  before  the  water 
flows  into  the  distributing-mains. 

197.  Effect  of  Distribution  on  Quality.  —  In  distributing  -  mains 
changes  in  character  of  water  may  also  occur.  The  temperature  varies 
considerably  during  passage  through  pipes,  and  this  has  some  effect  on 
the  living  organisms  of  the  same.  The  action  of  water  on  the  pipes  is 
considerable,  especially  if  derived  from  a  supply  that  is  poor  in  lime 
and  magnesia  salts.  Unless  protected,  the  pipes  are  liable  to  rust  and 
the  so-called  iron  "tubercles  "  form  on  the  inner  surface.  In  "dead 
ends,"  owing  to  the  stagnation  in  current,  the  water  may  acquire  a  dis- 
tinct chalybeate  taste  and  appear  unsightly  from  flakes  of  iron-rust. 
This  condition  is  much  aggravated  if  the  water  itself  contains  iron  in 
solution,  in  which  case  the  iron  bacteria  (Crenothrix)  are  able  to 
thrive.  Certain  kinds  of  waters,  as  those  rich  in  CO2  or  organic  acids, 
may  exert  a  solvent  action  on  service-pipes  if  they  are  made  of  lead  to 
such  an  extent  as  to  produce  lead  poisoning.  This  trouble  occurs 
most  frequently  in  connection  with  peaty  waters. 

Most  other  microscopic  organisms  are  reduced  in  number  in  the 
distributing-pipes.  If  the  source  of  supply  is  from  reservoirs  or  surface 
bodies,  it  is  apt  to  contain  algae  which  are  unable  to  live  in  darkness. 
Such  organisms  therefore  die  and  decay  rapidly  in  the  pipes,  and  if 
sufficiently  numerous  undesirable  odors  may  be  imparted  to  the  water, 
besides  furnishing  food  for  bacteria.  Many  organisms  are  deposited  by 
sedimentation,  particularly  in  pipes  on  an  "up-grade"  or  in  high 

*  Sometimes  a  limited  light  through  the  roof  of  the  reservoir  cover  will  permit 
certain  species,  as  Chlorococcus,  Asterionella,  Melosira,  and  Synedra,  to  develop,  as 
was  the  case  at  Dedham,  Mass.,  where  the  supply  was  drawn  from  a  covered  well. 


QUALITY  OF   WATER. 

buildings.  Animal  forms,  living  as  they  do  on  organic  matter,  are  able 
to  grow  under  such  conditions,  and  in  waters  supplied  from  surface 
sources  it  is  not  uncommon  to  find  the  inner  walls  of  the  mains  covered 
with  a  considerable  layer  of  ' '  pipe-moss  ' '  which  may  be  made  up  ol 
sponges,  Protozoa,  and  Bryozoa.  Ground-waters  are  not  so  likely  to 
be  troubled. 

Changes  occur  in  the  bacterial  content  of  water  during  distribution, 
but  sometimes  they  are  increased  and  again  they  may  be  diminished. 
There  does  not  appear  to  be  any  well-defined  law  regarding  their 
action. 

LITERATURE. 

Most  of  the  text-books  of  a  general  character  that  are  mentioned  under 
the  Literature  of  Chapter  VIII  also  include  the  subject  of  quality  of  water. 

The  following  papers  also  treat  the  different  phases  of  the  subject  of 
quality  of  water. 

Rafter,  Geo.  W.     Lake  Erie  as  a  Water-supply  for  Towns  along  its  Borders. 

Buffalo  Soc.  Nat.  Sciences,  Jan.  13,  1896. 
Hazen  and  Reynolds.     The  Water-supply  of  Chicago.     Amer.  Pub.  Health 

Assn.,  1893,  p.  146. 
Sedgwick,  W.  T.     Protection  of  Surface-waters  from  pollution.    Journ.  N.  E. 

W.  W.  Assn.,  Mch.  1897,  p.  245. 

Frankland,  P.  F.     The  Present  State  of  Knowledge  concerning  the  Self-puri- 
fication of  Rivers.     Eng.  News,  1891,  xxvi.  p.  218. 
Currier.     Self- purification  of  ,  Flowing  Water  and  the  Influence  of  Polluted 

Water  in  the  Causation  of  Disease.     Trans.  Amer.  Soc.  C.  E.,  1891, 

xxiv.  p.  21. 

Fitzgerald.  Lake  Temperatures.  Trans.  Am.  Soc.  C.  E.,  1895,  xxxiv.  p.  67. 
Leeds.  Report  on  Odors  and  Tastes  of  Brooklyn  Water.  Eng.  News,  1897. 

xxxvni.  p.  13. 
Farlow,  W.  G.     Relation  of  Certain  Forms  of  Algae  to  Disagreeable  Tastes 

and  Odors.     Science,  1883,  n.  p.  333. 
Forbes,  F.  F.     Relative  Tastes  and  Odors  Imparted  to  Water  by  Algae  and 

Infusoria.     Journ.  of  the  N.  E.  Water-works  Assn.,  1891,  vol.  vi. 
Jackson  and  Ellms.     Odors  and  Tastes  of  Surface-waters  with  Special  Refer- 
ence to  Anabaena.      Tech.  Quart.,  December,  1897. 
Whipple,    G.    C.     Report  on  Organisms  of  the  Boston   Water-supply.      19 

Rept.  of  the  Boston  Water-works,  1894. 
Calkins,  Gary  N.     Study  of  Odors  observed  in  the  Drinking-waters  of  Mass. 

24  Rept.  Mass.  Bd.  Health,  1892,  p.  355. 
Parker,  G.  H.     Rept.  upon  the  Organisms  (excepting  Bacteria)  found  in  the 

Waters  of  the  State.       Exam,   of   Water-supplies,    1890,    p.    579* 

Mass.  Bd.  Health. 

Winogradsky,  S.     Ueber  Eisenbakterien.     Bot.  Zeit,  1888,  Bd.  46. 
Zopf,  W.     Unters.  u.  Crenothrix  polyspora,  1879. 
Giard,  A.      Sur  la  Crenothrix  Kuhniana;  la  cause  de  1'infection  des  eaux  cto 

Lille.      Compt.  rendu  1'Acad.  d.  sc.,  1882,  xcv.  p.  247. 
Sedgwick,  W.  T.     On  Crenothrix  Kuhniana.     Tech.  Quart.,  1890,  p.  338. 


CHAPTER  X. 
COMMUNICABLE   DISEASES  AND  WATER-SUPPLIES. 

198.  Relation  of  Water-supplies  to  Disease  Dissemination. — The  key- 
note of  sanitary  science,  so  far  as  applied  to  the  investigation  of  water 
problems,  is  to  be  noted  in   the   relation  that  exists  between   com- 
municable or  transmissible  diseases  and  public  water-supplies.     That 
disease-producing  germs   may  find   their  way  into  the  human   body 
through  water  and  so  possibly  cause  outbreaks  of  different  maladies  has 
been  known  from  time  immemorial.      The  ancient  Romans  appreciated 
this  when  they  spent  so  much  time  and  labor  to  bring  their  water- 
supplies  through  their  magnificent  aqueducts  from  beyond  the  reach  of 
pollution. 

The  most  important  question  to  be  considered  in  connection  with 
any  water-supply  is:  (i)  whether  it  is  wholly  free  from  the  possibility 
of  distributing  disease ;  (2)  whether  it  is  likely  to  remain  in  such  a  con- 
dition. These  are  questions  of  much  more  importance  than  economy 
in  securing  or  distributing  water,  and  should  therefore  first  engage  the 
attention  of  the  sanitary  engineer.  Of  the  various  maladies  that  are 
transmissible  from  person  to  person,  only  a  limited  number  are  likely 
to  be  distributed  through  the  medium  of  water.  These  are  known  as 
water-borne  diseases  in  contradistinction  to  those  that  are  disseminated 
through  the  air  or  find  an  entrance  by  means  of  wounds. 

199.  The  Germ  Theory  of  Disease. — The  germ  theory  of  communi- 
cable diseases  is  now  so  definitely  established  that  it  is  unnecessary  to 
present  proof  in  detail  that  the  various  maladies  of  this  class  are  caused 
by  the  introduction  of  living  organisms  from  outside  of  the  body.     In 
connection  with  this  theory,  two  schools  have  arisen,  one  holding  to 
the  idea  that  each  disease  has  a  specific  cause,  an  organism  which  alone 
is  responsible  for  the  occurrence  of  the  pathological  condition.      The 
other  adheres  to  the  hypothesis  that  the  production  of  a  diseased  state 
requires  more  than  the  introduction  of  the  germ  associated  with  the 
malady.    According  to  this  school  the  organism  must  find  its  way  into 

181 


1 82  COMMUNICABLE  DISEASES  AND    WATER-SUPPLIES. 

a  susceptible  soil,  under  conditions  which  favor  the  production  of  the 
diseased  state. 

It  is  at  once  evident  that  these  theories  have  a  direct  bearing  upon 
questions  relating  to  sanitary  engineering.  If  the  introduction  of  the 
specific  germ  of  cholera  is  all  that  is  necessary  to  provoke  an  attack  of 
that  disease,  it  is  more  than  ever  necessary  that  all  cholera  organisms 
should  be  prevented  from  finding  their  way  into  waters  used  as  public 
supplies. 

200.  Specific  Nature  of  Water-borne  Disease  Germs.  —  In  the  case  of 
most  water-borne  diseases,  it  is  quite  generally  admitted  that  the  causal 
organism  is  more  or  less  sharply  differentiated  from  other  bacteria.     In 
one  case,  i.e.,  typhoid  fever,  the  specific  nature  of  the  organism  is  not 
defined  with  so  much  certainty.     Bacillus  typhosus,  the  typhoid  fever 
bacillus,  is  closely  related  to  the  common  intestinal  organism,  Bacillus 
coli  communis;    and    by  some   it   is  held  that  these   are  merely  two 
varieties  of  the   same  germ.*     The  preponderance  of  evidence,   how- 
ever, is  generally  believed  to  be  in  favor  of  the  specific  nature  of  the 
two  organisms  ;  yet  from  the  engineer's  point  of  view  it  does  not  matter 
much,  for  any  drinking-water  that  contains  evident  traces  of  intestinal 
discharges  certainly  should  not  be  regarded  as  a  safe  supply,  even  if 
the  possibility  of  human  wastes  finding  their  way  into  the  same  be 
wholly  excluded. 

201.  Diseases  Due  to  Parasitic  Intestinal  Worms.  —  Whether  fecal 
matter  from  distinctively  animal  sources  should  be  permitted  to  pollute 
drinking-water  is  a  somewhat  different  question,  for  the  diseases  inci- 
dent to  man  that  are  most  frequently  spread  by  means  of  the  water- 
supply  do  not  normally  occur  among  animals,  yet  the  possibility  exists 
that  larvae  and  eggs  of  parasitic  worms  may  find  their  way  into  water 
through  discharges  of  animals.     In  a  number  of  cases  these  parasites 
are  common  to  both  man  and  some  of  the  lower  animals,  and  hence 
the  danger  from   this  source  is  evident.     Among  the  more  common 
parasitic  worms  that  affect  man  are  the  pork  tape-worm  (Tcenia  solium), 
the   round    worm    (Ascaris   lumbricoides),    the   thread-worm    (Oxyuris 
vermicularis],  and  the  worm    causing  pernicious  anaemia  (Anchylosto- 
mum  duodenale).     These  worms,  while  affecting  the  human  species, 
also  find  lodgment  in  some  of  the  lower  animals.     In  such  cases  their 
intestinal  contents   may  contain  eggs  which  may  thus  find  their  way 
into  waters  through  pollution  of  the  same  with  animal  refuse,  but  in 
the  aggregate  the  danger  from  this  source  is  small. 

*  Hueppe,  Prin.  of  Back,  English  trans.,  p.  193. 


DISEASES    TRANSMISSIBLE  BY    WATER.  183 

INFECTIOUS    DISEASES   TRANSMISSIBLE   BY   WATER-SUPPLIES. 

202.  Conditions  Necessary  for  Infection. — The  danger   of  a  water- 
supply  serving  as  a  vehicle  for  the  transmission  of  disease  rests  (i) 
on  the  possibility  of  such  organisms  finding  their  way  into  potable  sup- 
plies, and  (2)  on  the  ability  of  the  bacteria  so  introduced  to  grow  in 
such  waters,  or  at  least  retain  their  vitality  for  sufficient  periods  of  time 
to  permit  of  infection. 

If,  under  ordinary  conditions,  water  is  not  a  medium  in  which  a 
pathogenic  organism  is  able  to  live,  then  there  is  practically  no  danger 
of  spreading  such  disease  in  this  way.  On  the  other  hand,  if  the 
specific  microbes  are  able  to  grow,  or  even  to  live  for  a  considerable 
period,  in  waters  that  normally  are  used  as  public  supplies,  and  these 
forms  are  also  liable  to  be  introduced  into  the  same,  then  the  danger 
from  this  source  is  well  worth  consideration. 

But  even  though  a  disease  germ  may  be  able  to  live  in  water,  it 
does  not  necessarily  follow  that  danger  to  human  beings  exists  on 
account  of  this.  Not  a  few  of  the  disease  bacteria  that  are  able  to 
retain  their  vitality  in  water  when  placed  under  experimental  conditions 
would  not  under  normal  circumstances  find  their  way  into  supplies. 

203.  Water-borne  Diseases  affect  Intestinal  Canal. — Only  those  dis- 
eases that  are  able  to  establish  themselves  in  the  alimentary  canal  are 
at  all  likely  to  be  transmitted  in  this  way.     This  might  include  those 
that  affect  the  throat,   as  diphtheria    or  scarlet  fever,  but,   generally 
speaking,  the  danger  is  confined  to  those  diseases  that  establish  them- 
selves in  the  intestines. 

In  some  cases,  as  in  typhoid  fever,  a  disease  can  enter  only  through 
a  single  organ  or  kind  of  tissue,  as  the  intestine  in  this  instance;  in 
other  cases,  as  in  anthrax  or  tuberculosis,  the  specific  cause  establishes 
itself  in  the  body  in  several  different  ways.  But  it  must  be  kept  in 
mind  that  there  are  numerous  human  diseases  that  do  not  obtain  a  foot- 
hold in  the  body  through  the  water  that  is  drunk.  These  may  there- 
fore be  practically  neglected  by  the  sanitary  engineer  in  his  work. 

204.  The  Most  Important  Water-borne  Diseases. — The  most  impor- 
tant diseases  to   consider   in   this   connection   are   typhoid   fever  and 
cholera.      These  are  the  distinctively  water-borne  diseases ;  and  while 
there  are  others  that  should  be  mentioned,  yet  practically  the  question 
of  pollution  with  specific  disease  bacteria  is  confined  to  a  discussion  of 
the  relation  that  these  two   maladies   have   to  public  water-supplies. 
Of  these  two,  in  this  country  under  normal  conditions,  cholera  is  of 
much  less  importance,  as  it  is  distinctively  an  Oriental  disease,  whose 


184         COMMUNICABLE  DISEASES  AND    WATER-SUPPLIES. 

natural  home  is  in  India.  Now  and  then,  on  account  of  the  close 
intercommunication  between  Europe  and  the  Orient,  and  the  laxity  at 
times  of  quarantine  regulations,  cholera  breaks  over  its  natural  bound- 
aries and  devastates  regions  widely  remote  from  its  native  home. 
Here  in  America  the  danger  from  the  disease  is  much  lessened,  unless 
a  widespread  epidemic  should  break  out  in  Europe. 

Typhoid  fever,  on  the  other  hand,  is  a  disease  that  is  naturally 
endemic  to  America  as  well  as  other  countries,  i.e.,  it  occurs  contin- 
ually with  more  or  less  regularity.  Neither  of  these  two  diseases  is 
contagious  in  the  strict  sense  of  that  term,  i.e.,  contracted  by  mere 
contact  with  an  affected  individual.  The  germ  causing  the  same  does 
not  travel  of  itself  through  the  air  as  in  the  case  of  smallpox  or  scarlet 
fever,  but  it  must  be  introduced  into  the  susceptible  organ,  the  intes- 
tine, through  the  medium  of  either  the  water  which  is  drunk  or  the  food 
which  is  eaten.  That  these  diseases  play  such  an  important  role  in 
human  affairs  is  a  striking  commentary  on  our  hygienic  methods  of  the 
present  day.  In  caste-ridden  India,  where  civilization  has  hardly  yet 
emerged  from  the  murky  darkness  of  superstition,  perhaps  it  is  excus- 
able that  cholera  should  remain  endemic;  but  among  the  civilized 
nations  of  Europe  and  America  it  is  indeed  humiliating  to  admit  that 
such  an  easily  preventable  disease  as  typhoid  fever  is  so  thoroughly 
entrenched. 

In  addition  to  these  two  principal  diseases  that  are  very  easily  spread 
by  means  of  polluted  water,  dysentery  and  diarrhceic  disturbances 
should  also  be  mentioned  as  traceable  to  a  similar  origin ;  but  these 
troubles  are  often  so  imperfectly  defined  that  they  are  not  with  certainty 
associated  with  any  definite  specific  organism. 

205.  Typhoid  Fever. — This  disease  is  essentially  an  intestinal  dis- 
ease, the  organism  of  which  finds  in  the  small  intestine,  especially  in 
the  lymph-glands  of  this  organ,  the  most  favorable  location  for  develop- 
ment. The  disease  organism,  Bacillus  typhosus,  multiplies  rapidly  in 
the  intestine,  and  is  evacuated  in  the  dejecta  and  sometimes  in  the  urine 
as  well.*  Carelessness  in  the  disposition  of  these  discharges  may  result 
in  surface-waters  becoming  polluted  with  the  same.  This  danger  from 
feces  has  long  been  known,  but  it  is  only  recently  that  the  danger  from 
infected  urine  has  been  thoroughly  appreciated.  Well-waters,  particu- 
larly those  that  are  from  open  and  relatively  shallow  wells,  are  also 
liable  to  become  infected. 

*  Gwyn  (Johns  Hopkins  Hosp.  Bull.,  June  1899)  states  that  from  20  to  30  per  cent 
of  all  typhoid  cases  show  this  condition.  A  most  serious  factor  in  this  connection  is 
their  persistence  for  months  in  such  large  numbers  after  convalescence.  Petruschky 
found  as  high  as  170,000,000  typhoid  organisms  per  cubic  centimeter  in  the  urine  of 
a  patient. 


DISEASES    TRANSMISSIBLE  BY    WATER.  185 

The  disease  organism  is  introduced  into  the  body  through  the  food 
and  drink.  Most  frequently  it  gains  entrance  by  means  of  polluted 
water,  but  quite  often  milk  and  solid  food  may  also  function  as  carriers 
of  contagion.  Even  in  milk  it  is  often  originally  introduced  from  con- 
taminated water  that  may  have  been  used  to  rinse  or  wash  the  milk- 
utensils,  as  in  the  very  severe  Stamford,  Conn.,  outbreak  in  1893, 
where  386  cases  of  the  disease  developed  in  a  period  of  a  few  weeks. 
Nearly  all  of  these  were  on  the  route  of  a  single  milkman ;  and  it  was 
further  shown  that  infection  of  the  milk  was  caused  by  rinsing  out  the 
cans  with  cold  water  from  an  infected  well,  after  they  had  been  well 
scalded. 

Within  recent  years  it  has  been  abundantly  demonstrated  that  flies 
and  insects  also  often  function  in  distributing  the  disease  by  infecting 
food.  To  such  a  cause  and  not  to  polluted  water-supplies  were  largely 
attributable  many  of  the  outbreaks  in  our  military  camps  during  the 
Spanish-American  war. 

The  period  of  incubation,  i.e.,  the  time  between  infection  and  the 
appearance  of  the  disease  in  the  affected  person,  is  somewhat  variable, 
ranging  from  nine  days  to  three  weeks,  the  symptoms  becoming  charac- 
teristic in  most  cases  in  about  two  weeks.  This  long  period  of  incuba- 
tion must  be  taken  into  consideration  in  searching  for  the  origin  of 
infection.  A  person  acquiring  the  disease  through  polluted  water 
would  therefore  not  show  any  evidence  of  the  same  for  some  time, 
and  it  is  on  this  account  easy  to  overlook  the  real  source  of  infection. 
Not  infrequently  sporadic  cases  may  be  acquired  in  other  cities  and  so 
disseminated  by  travelers  (Fig.  26).  Then,  again,  frequently  the  disease 
is  rather  light  in  character,  so  that  the  affected  person  is  not  confined 
to  the  house.  The  disease  is  often  spread  unwittingly  by  these  "  ambu° 
lating  "  or  "walking  "  typhoid  cases. 

By  many  it  is  believed  that  putrid  or  offensive  gases  emanating 
from  sewage  or  any  other  foul  source  predisposes  the  system  to  this 
disease.  On  the  basis  of  this  belief  it  is  generally  regarded  that 
sewer-gas  is  very  dangerous.  Some  experimental  results  obtained  by 
Alessi  *  seem  to  indicate  that  such  a  view  might  be  true,  but  this  is 
contradicted  by  Abbott, t  whose  experimental  investigations  seem  to 
indicate  that  such  gases  do  not  affect  the  health  of  animals  The 
mortality  of  laborers  in  the  sewer  systems  of  large  cities  or  in  con- 
nection with  sewage-disposal  plants  does  not  sustain  the  view  that 
inhalation  of  air  over  sewage  is  especially  dangerous.  j 

*  Cent.  f.  Bakt.,  1894,  XV.  p.  228. 

f  Trans,  of  Cong,  of  Amer.  Phys.  and  Sur.,  1894,  pp.  28-55. 


COMMUNICABLE   DISEASES   AND    WATER-SUPPLIES. 

The  mortality-rate  in  typhoid  fever  varies  considerably  in  different 
outbreaks,  ranging  from  a  few  to  over  20  per  cent,  and  averaging  on 
the  whole  about  10  per  cent  of  the  case-rate. 

Although  the  disease  at  present  is  much  more  wide-spread  than 
necessary  (owing  to  our  failure  to  regard  hygienic  measures  that  would 
limit  its  distribution),  still  it  is  diminishing  rapidly  in  amount  as  is  indi- 
cated by  the  data  compiled  from  the  Massachusetts  vital  statistics. 

TABLE   NO.  29. 

DECREASE   IN   TYPHOID    FEVER    IN   MASSACHUSETTS    FROM    1871-1897. 

Typhoid  Death  Rate       Percentage  of  Typhoid 
per  10,000  Population.    Deaths  to  Total  Mortality. 

1871-1875 
1876-1880 
1881-1885 
1886-1890 
1891-1895  3.25  1.62 

1896  2.77  1.46 

1897  2.37  1.42 

In  the  five  large  cities  in  the  United  States  the  percentage  of 
typhoid  deaths  to  total  mortality  has  ranged  as  follows  from  1870-95, 
inclusive  : 

TABLE   NO.  30. 

PERCENTAGE    OF   TYPHOID    DEATHS    TO    TOTAL    MORTALITY    IN    FIVE   AMERICAN    CITIES. 


New  York  ........................  1.12  0.7  1.8 

Brooklyn  .........................  0.75  0.6  i.i 

Boston  ............................  1.93  1.2  3.0 

Philadelphia  ......................  2.99  1.4  4.0 

Chicago  ..................  ........  3.66  i.  08  7.2 

206.  Typhoid  Fever  and  Sewage  Pollution.  —  The  history  of  almost 
every  large  city  has  been  that  with  the  growth  in  population  and  con- 
sequent increase  in  sewage  the  amount  of  typhoid  fever  has  steadily 
increased.  This  is  particularly  striking  in  those  cities  that  are  situated 
on  river  systems  or  large  bodies  of  water  where  surface-waters  serve 
the  dual  purpose  of  public  water-supply  and  sewage  disposal. 

On  river  systems,  particularly  in  the  more  thickly  populated  regions 
of  this  country  and  Europe,  cities  frequently  draw  their  public  supplies 
from  running  streams  that  may  have  been  polluted  by  the  sewage  of 
towns  above  them.  With  the  natural  growth  in  population  the  zone 
of  pollution  in  the  stream  is  constantly  widening,  and  hence  supplies 
from  rivers  which  at  one  period  might  have  been  satisfactory  are  con- 
tinually being  endangered. 


DISEASES    TRANSMISSIBLE  BY    WATER. 


I87 


The  increase  in  typhoid  fever  in  such  cases  is  generally  gradual, 
but  at  intervals  an  especially  severe  outbreak  in  any  one  town  will 
often  be  reflected  in  other  outbreaks  in  towns  situated  lower  down  the 
This  synchronous  development  of  the  disease  proves  the  fact 


river. 


beyond  dispute  that  the  rise  and  fall  of  typhoid  is  often  closely  related 
to  pollution  of  municipal  supplies  from  sewage. 

207,  Mohawk  Valley  Epidemic. — A   most  instructive  case  of  this 
simultaneous  development  of  disease  due  to  sewage  pollution   is  seen 


x 

"~ll_ans')ngburcfh 


to  Co/x>e-s 

Cohoes  ;&  Wesf  Troy    J 

Wesf  Troy  -fo^l/Aany     6 

Wafer  /nfo/fes  fa 


FIG.  25. — DISTRIBUTION  OF  TYPHOID  FEVER  IN  MOHAWK-HUDSON  VALLEY. 

(Adapted  from  Mason.) 
Typhoid  epidemics  shaded  (relative  intensity  of  outbreak  denoted  by  shading). 

in  the  series  of  typhoid  epidemics  that  occurred  in  the  towns  in  the 
valley  of  the  Mohawk  and  Hudson  rivers  in  1890-91. 

In  July,  1890,  typhoid  became  epidemic  in  Schenectady  and  con- 
tinued until  April,  1891.  Seventeen  miles  down  the  Mohawk  is 
Cohoes,  a  city  of  about  22,000.  Typhoid  broke  out  here  in  October, 
1890,  and  before  April,  1891,  there  had  been  1000  cases.  The  disease 
was  exceptionally  mild;  but  notwithstanding  this  the  typhoid  death- 
rate  for  the  period  of  the  epidemic  was  equal  to  an  annual  death-rate 
of  45  per  10,000  inhabitants,  or  about  12-15  times  the  normal. 

West  Troy,  taking  its  supply  also  from  the  Mohawk  above  Cohoes 
(see  map),  suffered  from  an  epidemic  from  November,  1890,  till 
February,  1 891 ,  except  for  a  brief  period  when  the  supply  of  the  village 


1  88  COMMUNICABLE   DISEASES  AND    WATER-SUPPLIES. 

of  Green  Island  was  used.  Six  miles  below  West  Troy  is  Albany. 
Here  again  the  disease  became  epidemic  in  December,  lasting  through 
the  spring.  Waterford,  Lansingburgh,  and  Troy  took  their  supply 
from  other  sources  than  the  Mohawk,  or  the  Hudson  below  the  junction 
with  the  former  stream.  So  far  as  this  outbreak  was  concerned  they 
escaped  entirely. 

The  progressive  development  of  the  disease  in  all  of  those  towns 
that  used  water  from  the  Mohawk,  and  its  absence  in  other  towns 
situated  on  the  Hudson  that  were  supplied  from  other  sources,  shows 
conclusively  the  influence  which  the  sewage  pollution  of  Schenectady 
and  other  upper  towns  had  on  the  distribution  of  the  disease. 

208.  Lowell-Lawrence  Epidemic.  —  A  similar  development  was  also 
noted  in  the  case  of  the  towns  of  Lowell  and  Lawrence  on  the  Merri- 
mack  River  in  Massachusetts.  In  1890-91  an  especially  severe  outbreak 
of  typhoid  occurred  in  Lowell  which  was  traced  to  the  water-supply. 
The  source  of  supply  was  the  river-water,  and  Sedgwick  showed  that 
the  probable  origin  of  the  polluted  condition  was  attributable  to  several 
cases  of  the  disease  at  North  Chelmsford,  a  small  village  situated  three 
miles  above,  on  a  tributary  of  the  Merrimack.  These  cases  occurred 
in  August,  September,  and  October. 

The  sewage  of  Lowell  empties  into  the  Merrimack,  and  after  8  hours' 
flow  the  river-water  is  utilized  by  the  city  of  Lawrence,  9  miles  below. 
Water  polluted  by  the  sewage  of  Lowell  might  thus  reach  Lawrence 
the  same  day.  It  would  take  several  days  (7-10)  to  pass  through  the 
supply-reservoir  before  it  found  its  way  into  the  service-pipes.  From 
an  inspection  of  Table  3  1  the  direct  relation  between  the  outbreak  in 
Lawrence  and  the  polluted  river-water  derived  from  Lowell  is  evident. 

TABLE    NO.   31. 

RELATION    OF  TYPHOID    OUTBREAK    IN    LOWELL   AND   LAWRENCE. 


Deaths  from  Typhoid  in 
September,  1890       . 

Lowell. 

8 

Lawrence. 

•5 

October          **         

10 

1 

November      ** 

28 

7 

December      "     

26 

IQ 

January,  1891 

IQ 

IQ 

February    "     

II 

March 

.    10 

6 

209.  Pollution  of  Lake  Towns.  —  Pollution  of  water-supplies  from 
sewage  is  not  confined  to  river  towns.  Cities  situated  on  lakes,  even 
on  our  Great  Lakes,  frequently  suffer  from  contamination  of  their  sup- 
plies through  disposing  of  their  sewage  in  the  same  way.  This  is 


DISEASES    TRANSMISSIBLE  BY  WATER.  189 

noted  in  a  striking  manner  in  the  case  of  Chicago,  which  takes  its 
supply  from  Lake  Michigan.  Although  a  portion  of  its  sewage  has 
been  pumped  for  a  number  of  years  into  the  old  Illinois  and  Michigan 
Canal,  still  the  pollution  of  the  lake-water  has  been  constantly  increas- 
ing through  the  drainage  of  the  Chicago  River  and  also  the  numerous 
sewer-outfalls  that  empty  directly  into  the  lake.  Through  the  custom 
of  emptying  into  the  lake  the  dredge-dumpings  from  the  river,  the 
water-supply  has  also  been  grossly  polluted  at  times  and  has  caused 
epidemics  of  typhoid.* 

The  earliest  water-intakes  were  located  only  a  short  distance  from 
shore.  These  have  been  gradually  extended  into  the  lake  from  I  to  2 
miles,  but  the  endemic  condition  of  typhoid  fever  in  the  city  and  the 
enormous  increase  in  1891  led  to  the  extension  of  the  main  tunnel  to 
4  miles  in  1892,  after  which  the  amount  of  typhoid  rapidly  decreased, 
as  shown  in  the  following  figures: 

TABLE   NO.    32. 

TYPHOID   DEATH-RATES   IN  CHICAGO    PER    IO.OOO  POPULATION  BEFORE  AND  AFTER  THE 
FOUR-MILE   EXTENSION    OF   THE   WATER-INTAKE. 


'86 

"87 

'88 

'89 

'90 

'91 

'92 

Av.  7  yrs. 

6.8 

5.0 

4-7 

4.8 

8.3 

16 

10.4 

8.0 

'93 

'94 

'95 

'96 

'97 

•98 

'99 

Av.  7  yrs. 

4.2 

3-1 

3-2 

4.6 

2.7 

3-8 

2.5 

3-4 

Even  the  relative  immunity  obtained  by  the  four-mile  tunnel  was 
not  of  long  duration,  for  in  a  few  years  it  was  not  uncommon  to  find  at 
times  that  the  water  was  polluted.  A  heavy  rainfall  that  would  flush 
out  the  river  would  frequently  pollute  the  lake  out  to  the  four-mile  in- 
take. Even  with  the  inauguration  of  the  Sanitary  Drainage  Canal  in 
1900,  which  removed  the  larger  part  of  the  sewage  from  the  lake, 
pollution  of  the  supply  occurs  from  time  to  time  due  to  the  increased 
pollution  yet  discharged  into  the  lake.  This  is  being  gradually 
remedied  by  the  construction  of  a  system  of  intercepting  and  large 
lateral  sewers. 

210.  Typhoid  and  Polluted  Wells.  —  Although  the  larger  epidemics 
of  typhoid  fever  are  necessarily  connected  with  impure  municipal  water- 
supplies,  still  it  also  frequently  happens  that  polluted  wells  are  the 
means  of  distributing  the  virus  of  the  disease.  The  opportunity  for 

*  Bull,  of  Chicago  Health  Dept.,  Aug.  1899. 


190 


COMMUNICABLE  DISEASES   AND    WATER-SUPPLIES. 


infection  is  considerably  greater  in  the  case  of  private  or  public  wells, 
but  the  spread  of  the  disease  is  likely  to  be  more  restricted  because  of 
the  smaller  number  of  users ;  but  on  the  whole  the  aggregate  of  typhoid 
cases  that  are  infected  in  this  way  frequently  exceeds  that  caused  by 
polluted  general  supplies.  It  often  happens  that  persons  acquire  the 
disease  in  other  towns  than  where  the  disease  first  becomes  manifest 
/'see  Fig.  26),  but,  excluding  this,  by  far  the  larger  amount  of  typhoid 
fever  incident  to  polluted  water  that  occurs  in  other  than  urban  popu- 


FIG.  26. — MOVEMENTS  OF  CONTAGIUM  OF  TYPHOID  FEVER.     (Mich.  Board  of  Health.) 
Direction  of  arrows  indicates  movement  of  disease  and  shows  how  new  foci  are 
established  by  importing  cases  from  without. 

lations  must  come  from  infected  wells.  Even  in  cities  a  considerable 
proportion  of  this  disease  is  attributed  to  the  use  of  old  wells.  This  is 
particularly  the  case  in  the  more  congested  poorer  quarters,  where  these 
older  sources  of  supply  are  retained  much  longer  than  in  the  newer  and 
better  built  portions  of  towns.  In  1889  in  Washington  626  fatal  cases 
of  typhoid  occurred  in  families  using  water  from  about  300  different 
wells,  a  sanitary  record  for  our  capital  city  that  is  indeed  humiliating. 

The  general  decline  in  typhoid  death-rates  in  cities  coincides  in  a 
remarkable  way  with  the  introduction  of  public  water-supplies,  as  has 
been  noted  especially  in  Massachusetts  (Fig.  27).* 

*  28  Kept.  Mass.  Bd.  Health,  1896,  p.  781. 


DISEASES    TRANSMISSIBLE  BY    WATER.  IQI 

211.  Outbreaks  Inaugurated  from  Single  Cases. — While  the  con- 
tamination of  municipal  water-supplies  is  generally  due  to  municipal 
sewage  pollution,  still  it  may  at  times  happen  that  a  single  case  oi 
disease  may  be  the  means  of  inaugurating  an  outbreak,  as  in  the 
Plymouth,  Pa.,  case.  This  epidemic,  consisting  of  over  1 100  cases  in 
a  town  of  8000  people,  had  its  origin  through  the  pollution  of  the 


/856-6S 


/&66-7S 


/d  76-65 


Death  f?<rfe  fro/77  Typho/af  Ferer  feer  /OO,OOO  

Perct/tfof  Popu/af/ofi  nof  supptied nvM  PU&//C  Wafer- 

FIG.  27. — DECREASE  IN  TYPHOID   DEATH-RATES  COINCIDENT  WITH   INTRODUCTION 
OF  PUBLIC  WATER-SUPPLIES.     (Mass.) 

impounded  drinking-water  by  the  fecal  discharges  of  a  single  patient. 
To  prevent  infection  of  the  family  vault,  the  dejecta  were  deposited  on 
the  surface  of  the  snow.  Soon  after,  heavy  rains  washed  the  frozen 
hillsides,  the  natural  surface-drainage  discharging  into  the  stream  that 
fed  the  supply-reservoir.  Within  about  two  to  three  weeks  a  very  pro- 
nounced epidemic  occurred  that  was  confined  closely  to  the  patrons  of 
the  municipal  water-supply. 

212.  Typhoid  Rates  an  Index  of  Quality  of  Water. — A  study  of  the 
death-rate  or  case-rate  of  typhoid  fever  in  various  towns  and  cities  for 
a  number  of  years  illustrates  in  a  striking  way  the  relation  that  exists 
between  this  disease  and  the  general  character  of  the  public  water- 
supply.  To  some  extent,  typhoid  may  be  introduced  into  a  city  from 
an  external  source  (Fig.  26).  This  factor  is  generally  more  important 
in  the  smaller  towns  in  which  the  transient  population  is  relatively  large, 
as  in  mining  and  lumbering  regions.  In  some  degree,  the  disease  may 
also  be  traced  to  other  causes  than  impure  water,  but  by  far  the  larger 
majority  of  cases  are  attributable  to  infection  of  this  character.  Cities 
deriving  their  supply  from  sources  in  which  the  probability  of  pollution 
is  excluded  have  as  a  rule  a  very  low  typhoid  death-rate ;  those,  on  the 
other  hand,  using  surface-waters  (impounded  or  streams)  generally 
show  an  increase  in  this  rate.  Hill  *  has  classified  cities  on  the  basis 

*  Public  Water-supplies,  p.  70. 


.192 


COMMUNICABLE  DISEASES  AND    WATER-SUPPLIES. 


of  their  death-rates  from  this  disease  into  seven  groups,  beginning  with 
those  having  a  typhoid  death-rate  of  ten  or  less  per  100,000  popula- 
tion, and  increasing  each  group  by  10.  The  seventh  class  embraces 
all  cities  whose  typhoid  death-rate  exceeds  60  per  100,000.  It  is  a 
significant  fact  that  reflects  upon  our  sanitary  methods  in  this  country 
to  observe  that  there  is  no  American  city  in  Class  I  or  II  with  the 
exception  of  New  York  and  Brooklyn.  Hill  has  even  suggested  that 


Population  in  Millions 
dr  7     "      '     "     * 


Typhoiof  Fe«r  Death  Rate  per  100,000. 


FIG.  28. — RELATION  OF  TYPHOID  DEATH-RATE  TO  CHARACTER  OF  WATER-SUPPLY 
IN  EUROPEAN  AND  AMERICAN  CITIES  ;  ALSO  POPULATION  SUPPLIED  FROM  EACH 
SOURCE.  (Fuertes.) 

contracts  for  supplies  should  be  made  on  the  basis  of  a  certain  death- 
rate  from  typhoid,  but  to  determine  the  effect  of  any  given  improvement 
like  this  requires  the  collection  of  data  for  several  years,  and  would 
therefore  seem  impracticable  for  this  purpose. 

Fuertes  *  arranges  these  statistical  data  on  the  basis  of  the  kind  of 
water  furnished  each  municipality,  as  mountain  spring,  filtered  water, 
ground- water,  surface-water  (streams,  impounded  waters,  and  lakes). 
In  Fig.  28  the  limits  between  which  75  per  cent  of  the  death-rates  per 
100,000  may  be  expected  are  shown  for  the  different  kinds  of  waters 
used ;  also  the  population  using  each  class.  Of  the  total  population  as 

*  Water  and  Public  Health,  p.  32. 


DISEASES    TRANSMISSIBLE  BY    WATER.  1 93 

charted  (over  33,000,000),  20,000,000  are  in  European  cities,  the 
remainder  in  America.  Over  75  per  cent  of  the  total  European  popu- 
lation here  represented  have  a  better  supply  than  an  impounded  reser- 
voir, like  the  Croton  supply  of  New  York,  while  over  75  per  cent  of 
the  supplies  furnished  American  cities  are  below  this  standard. 

213.  Diminished  Typhoid  Rates  Incident  to  Improved  Supplies. — 
From  the  typhoid  death-rates  it  is  very  evident  that  the  water-supplies 
of  European  cities  are  much  better  than  those  in  America.  This  con- 
dition, however,  has  not  always  obtained,  as  in  most  cases  European 
municipalities  have  had  to  pay  the  penalty  of  impure  water  by  high 
death-rates  before  their  supplies  were  bettered.  The  much  denser 
population  per  square  mile  in  Europe  increases  of  course  the  amount 
of  pollution  in  most  surface-waters,  and  makes  it  thereby  increasingly 
difficult  for  large  cities  to  secure  adequate  supplies  that  are  beyond  the 
taint  of  suspicion.  In  mountainous  regions  pure  natural  waters  can 
frequently  be  obtained,  but  in  the  cities  situated  on  the  seacoast  and  in 
the  plains  region  sufficient  natural  supplies  of  pure  surface-water  are 
to  be  had  only  in  exceptional  instances.  This  has  led  to  the  purifica- 
tion of  waters  taken  from  available  sources  of  supply.  The  diminished 
typhoid  death-rates  under  these  conditions,  as  compared  with  those  that 
obtained  before  such  improvements  were  made,  indicate  in  the  most 
conclusive  manner  the  close  relation  that  exists  between  the  quality  of 
water-supplies  and  public  health,  so  far  as  water-borne  diseases  are 
concerned.  These  diminished  typhoid  death-rates,  however,  have  not 
been  gained  entirely  by  securing  an  unpolluted  or  a  purified  water- 
supply,  but  in  part  through  the  introduction  of  improved  systems  of 
sewerage. 

In  Zurich  the  introduction  in  1885  of  new  filters  carefully  controlled 
caused  the  following  marked  decrease  in  typhoid  rates  per  100,000 
population : 

TABLE  NO.  33. 

TYPHOID    DEATH-RATES    IN    ZURICH,    SWITZERLAND,    PER  IOO,OOO  POPULATION,  IN 
RELATION   TO   IMPROVEMENTS    IN   WATER-SUPPLIES. 

Before  Improvement. 

Av.  7  yrs. 

*79  '80  '81  '82  '83  '84  '85 

33  80  43  48  27  174  no  73-6 

After  Improvement. 

Av.  9  yrs. 

'86         '87         '88         '89         '90         '91         '92          93         '94 
10          13  8  9  10  8          8.5        7.5          7  9.0 


194          COMMUNICABLE   DISEASES  AND    WAITER-SUPPLIES. 

In  the  case  of  Munich  the  diminution  in  typhoid  losses  was  coinci- 
dent with  the  installation  of  the  sewerage  system,  although  the  water- 
supply  was  not  changed  until  several  years  afterward. 

Fig.  29  shows  the  pronounced  drop  in  the  typhoid  rate  and  the 
relation  of  the  same  to  sewerage  introduction. 


S  s 


maximum  during 
declining  in  the 
30  indicates  this 
Of  course  during 


FIG.  29.— TYPHOID  DEATH-RATE  IN  MUNICH  ;  RELATION  OF  SAME  TO  INTRODUCTION 
OF  SEWERAGE  AND  WATER-SUPPLY.     (Fuertes.) 

214.  Seasonal  Distribution  of  Typhoid  Fever. — Typhoid  fever  does 
not  rage  with  equal  severity  throughout  the  entire  year.      Usually  the 

case-rate  increases  in  late  summer  and 
fall,  often  reaching  a 
the  winter  and  then 
spring  months.  Fig. 
unequal  distribution, 
outbreaks  of  this  disease  this  general  rule 
does  not  obtain,  as  infection  may  rapidly 
pass  from  one  person  to  another.  Wood- 
head*  attributes  this  higher  case-rate  in  the 
fall  to  the  higher  temperature  of  the  water, 
facilitating  the  growth  of  the  typhoid 
organism,  but  this  point  is  by  no  means 
thoroughly  established.  The  ability  of 
the  organism  to  retain  its  vitality  when  frozen,  even  though  it  is  not  a 


FIG.  30. — SEASONAL  DISTRIBUTION 
OF  TYPHOID  FEVER.   (Abbott.) 


*  Roy.  Com.  on  Met.  Water-supply,  1893,  p.  506. 


DISEASES    TRANSMISSIBLE  BY    WATER.  IQ5 

spore-producing  germ    (184,    223),    shows   how   the   disease   may  be 
spread  even  in  winter. 

215.  Asiatic  Cholera, — While  cholera  is  a  disease  that  is  naturally 
"at  home"  in  the  Orient,   particularly  in  India  in  the  delta  of  the 
Ganges,  still  ever  and  anon  it  breaks  over  the  boundaries  that  naturally 
limit  it  and  becomes  epidemic  among  western  nations.      Europe  has 
been  visited  with  this  disease  a  number  of  times  during  the  last  century, 
the  last  outbreak  occurring  in  Germany  in    1892-3.      It  has  less  fre- 
quently invaded  this  country,  although  eight  epidemics  are  recorded 
since   1832.     The  epidemic  of  that  year  and  those  of   1853-54  and 
1873  were  the  most  severe.     Since  the  latter  date,  the  disease  has  not 
occurred  in  this  country. 

Like  typhoid  fever  it  is  primarily  an  intestinal  disease,  the  organism 
associated  with  it  developing  luxuriantly  in  the  intestine  and  therefore 
occurring  in  large  numbers  in  the  dejecta  of  cholera  patients.  This 
causative  organism  was  discovered  by  Koch  in  1884  in  India,  where  he 
succeeded  in  isolating  it  from  the  intestinal  contents  of  cholera  patients ; 
also  rinding  the  same  in  water  from  an  open  uncovered  drinking-tank. 

216.  Cholera  Outbreaks  traced  to  Water-supplies. —In  1854  London 
was  visited  with  a  severe  epidemic.     The  cholera  death-rate  in  that 
portion  of  the  city  supplied  by  one  company  that  drew  its  supply  from 
the  polluted  Thames  was  154  per  10,000,  while  in  another  quarter  fed 
with  an  unpolluted  supply  there  were  only  17  deaths  per  10,000. 

The  1892-93  outbreak  in  Europe  gave  ample  opportunity  for  the 
study  of  the  disease  in  the  light  of  modern  methods.  Although  the 
specific  organism  had  been  found  before  in  several  cases  associated  with 
epidemics  of  the  disease,  many  new  data  were  gathered  at  this  time  and 
the  relation  of  the  cholera  organism  to  water-supplies  thoroughly  con- 
firmed by  bacteriological  examinations.  In  these  studies  it  was  also 
found  that  surface-waters  not  infrequently  contain  other  bacteria  of  the 
spirillum  type.  Many  of  these  closely  simulate  the  cholera  or  comma 
organism,  as  it  is  sometimes  called  on  account  of  its  shape,  but 
Pfeiffer's  test  and  certain  cultural  methods  permit  of  a  ready  differentia- 
tion (149). 

The  most  striking  illustration  of  the  way  in  which  the  disease  is 
spread  by  water-supplies  is  shown  in  the  Hamburg  outbreak.  Ham- 
burg, a  city  containing  at  that  time  a  population  of  640,000,  and 
Altona,  a  city  of  150,000  people,  are  situated  on  the  River  Elbe  near 
its  mouth.  The  two  cities  are  practically  one,  as  they  merge  into  each 
other,  although  they  have  a  separate  city  government.  Hamburg 
at  this  time  drew  its  water-supply  from  the  Elbe  some  distance  above 


196          COMMUNICABLE  DISEASES  AND     WATER-SUPPLIES. 

the  city.  Altona,  situated  just  below  and  forced  also  to  use  the  Elbe 
water,  took  it  at  a  point  8  miles  down-stream,  treating  it  by  sand  filtra- 
tion because  of  its  impure  condition.  Hamburg  therefore  received 
unfiltered  Elbe  water,  subject  of  course  to  possible  pollution ;  Altona 
used  filtered  river-water,  taken  from  the  stream  after  it  had  received  the 
sewage  of  over  800,000  people.  Cholera  broke  out  in  the  fall  of  1892, 
and  during  this  epidemic  there  were  17,000  cases  (16,800  in  less  than 
two  months)  in  Hamburg  with  over  8600  deaths,  while  during  the 
same  time  there  were  only  about  500  cases  with  about  300  deaths  in 
Altona.  Hamburg  with  its  unfiltered  river-supply  had  a  case-rate  of 
about  263  per  10,000  and  a  death-rate  of  134,  while  in  Altona  the 


FIG.  31.  HAMBURG-ALTONA  EPIDEMIC  OF  CHOLERA  IN  1892. 

Deaths  from  cholera  are  shown  in  district  400  meters  each  side  of  Hamburg-Altona 
boundary.  Section  in  Hamburg  marked  C  was  supplied  with  Altona  water  and 
wholly  escaped  the  disease. 

case-rate  was  38.1  and  the  death-rate  21.3.  Of  the  number  in  the 
latter  city  it  must  be  remembered  that  the  disease  was  contracted  in 
many  cases  by  people  who  worked  in  Hamburg  but  lived  in  Altona. 
One  block  of  buildings  in  Hamburg,  containing  about  400  people,  re- 
ceived its  water-supply  from  Altona  rather  than  Hamburg  on  account 


DISEASES    TRANSMISSIBLE  BY    WATER. 

of  local  difficulties  in  connecting  the  main.  This  spot  (C  on  map), 
although  surrounded  with  cholera  cases,  remained  free  from  the  disease. 
Several  of  the  large  hospitals,  garrisons,  and  prisons  in  Hamburg  that 
used  other  water  than  the  municipal  supply  escaped  with  little  or  no 
disease.  The  history  of  the  epidemic  shows  in  the  most  conclusive 
manner  that  the  river-water  was  the  means  by  which  the  disease  was 
spread.  In  fact,  the  cholera  spirillum  was  isolated  not  only  from  water 
taken  from  the  Elbe,  but  also  in  one  of  the  Altona  filter-basins  before 
the  water  was  submitted  to  filtration.* 

217.  Anthrax. — This  disease  is  not  often  disseminated  by  means  of 
the  drinking-water,  but  waters  of  surface  origin  may  receive  drainage 
from  fields  on  which  the  disease  may  be  present,  and  so  become  con- 
taminated.     This  condition  is  especially  liable  to  occur  in  those  regions 
(Europe,  Asia,  and  Africa)  where  the  disease  is  severe.      Here  in  this 
country  it  is  not  established  except  in  a  few  localities  (Lower  Missis- 
sippi valley,  Lower  Delaware  River,  etc.). 

Rivers  are  more  apt  to  be  the  distributive  agents  so  far  as  waters 
are  concerned.  On  account  of  using  hides  and  skins  imported  from 
infected  regions  refuse  from  tanneries,  brush-factories,  and  morocco- 
shops  disposed  of  in  running  streams  may  often  be  the  cause  of  out- 
breaks along  watercourses. 

A  striking  instance  came  under  the  writer's  attention  in  1899.  The 
Black  River,  for  a  distance  of  10  miles  below  Medford,  Wis.,  was  pol- 
luted by  tannery  refuse.  Stock  (cattle  and  horses)  contracted  anthrax 
by  drinking  the  river-water,  by  grazing  on  lowlands  that  had  been 
subjected  to  overflow  in  the  spring,  and  by  eating  hay  that  had  been 
gathered  from  the  inundated  marshes.  In  caring  for  the  affected  stock 
several  persons  also  became  infected.  The  disease  germ  was  introduced 
from  a  tannery  in  which  Chinese  hides  were  being  handled. 

Diatroptofft  notes  the  detection  of  the  specific  organism  in  the  case 
of  a  well-water.  The  water  from  this  well  served  to  infect  a  herd  of 
sheep.  The  writer  in  the  Medford  outbreak  succeeded  in  isolating  the 
disease  organism  from  a  pond  that  had  become  infected  by  surface 
drainage  from  fields  on  which  cattle  had  died  from  anthrax. 

218,  Other  Water-borne  Diseases. — In  addition  to  the  above,  a  con- 
siderable number  of  other  diseases  are  also  distributed  more  or  less  fre- 
quently by  the  aid  of  water.      In  some  cases  the  causal  organism  that 
produces  the  disease  is  not  yet  known,  but  the  manner  in  which  the 
outbreak  is  disseminated  leaves  no  room  for  doubt  as  to  the  probability 
of  water  functioning  in  its  spread.      The  winter  outbreaks  of  cholera 

*  Zeit.  f.  Hyg.,  XIV.  p.  337.  \  Ann.  Past.,  1893,  vii.  p.  286. 


198  COMMUNICABLE  DISEASES  AND    WATER-SUPPLIES. 

infantum  that  have  occurred  in  Hamburg  and  Altona  have  been  traced 
directly  to  the  use  of  raw  or  imperfectly  filtered  Elbe  water.* 

219.  Gastro-intestinal  Disturbances. — As  representing  this  class  of 
diseases  may  be  mentioned  gastro-intestinal  catarrhs.     In  some  cases 
a  diarrhceic  condition  may  be  produced  as  the  result  of  the  presence  of 
suspended  matter.      In  a  number  of  instances,  epidemics  of  intestinal 
catarrhs  have  been  associated  with  the  pollution  of  waters  with  organic 
matter  from  various  sources.     The  Long  Branch, t  N.  J.,  outbreak  was 
ascribed  to  the  use  of  peaty  water,   but  it  was  not  definitely  shown 
whether  the  disturbance  was  due  to  the  organic  matter  of  peaty  origin 
or  to  organisms  that  were  present  in  such  water. 

Wright  J  instances  an  outbreak  in  Buffalo  that  was  confined  entirely 
to  persons  who  used  water  from  a  series  of  shallow  wells  in  a  certain 
region  of  the  city. 

Cameron  §  records  an  epidemic  in  a  military  school  in  Dublin  where 
150  persons  were  afflicted.  The  trouble  was  traced  to  a  ground-water 
that  was  found  to  be  rich  in  micro-organisms. 

In  1 894  a  very  extensive  outbreak  of  an  enteric  disease  appeared 
in  Lisbon,  ||  Portugal.  In  three  months  over  15,000  people  were 
afflicted.  The  symptoms  of  the  disease  appeared  like  cholera  in  many 
ways,  but  the  fact  that  only  one  person  died  from  the  same  indicated 
at  least  that  the  germ  in  its  pathogenic  properties  was  much  different 
from  true  Asiatic  cholera.  The  organism  producing  the  outbreak  was 
readily  separated  from  fecal  discharges  of  affected  persons,  and  was  also 
found  in  the  water-supply  of  the  city.  It  bore  a  striking  resemblance 
to  the  comma  bacillus  of  cholera.  The  protection  afforded  by  the  use 
of  household  filters  demonstrated  conclusively  that  the  disease  was  dis- 
tributed by  the  way  of  the  water-mains. 

220,  Dysentery, — Although  it  is  quite  probable  that  dysentery  may 
be  caused  by  more  than  one  kind  of  organism,  the  relation  of  diseases 
of  this  class  to  polluted  waters  is  now  quite  generally  accepted.     The 
severe  form  of  the  disease  that  occurs  in  the  tropics  is  ascribed  to  the 
development  of  an  animal  parasite,  Amoeba  colt,  while  the  disease  as  it 
appears  in  some  other  countries  seems  to  be  associated  with  certain 
bacteria.      As  these  organisms  have  riot  been  definitely  determined  in 
water-supplies,  the  supposed  connection  between  them  and  water  does 
not  rest  upon  a  thoroughly  established  scientific  basis,  but  is  based 
upon  the  distribution  of  the  disease  and  other  epidemiological  data. 

*  Hazen.     Filtration  of  Public  Water-supplies,  p.  228. 

f  Mason.     Water-supply,  p.  II.  \  Sanitary  Record,  IV.  p.  185. 

§  Dublin  Jour.  Med.  Sc.t  i.  p.  535.          |  Cent.  f.  J3akt.t  1894,  XVI.  p.  401. 


VITALITY  OF  PATHOGENIC  BACTERIA   IN   WATER.  199 

221.  Malaria. —  Regarding  the  spread  of  malaria  by  means  of  water- 
supplies,  not  much  definite  information  that  is  scientifically  established 
is  at  hand,  although  the  general  belief  has  been  that  the  disease  is  some- 
times spread  in  this  way.     The  recent  establishment  of  the  mosquito 
theory  of  infection  shows,  however,  that  water  is  necessary  for  the  con- 
tinuance of  the  disease,  although  there  is  no  evidence  that  the  malarial 
parasite  is  introduced  with  the  water  that  is  ingested,  even  though  such 
water  might  contain  the  larvae  of  the  spotted-wing  mosquito  (Anopheles) 
that  is  now  known  to  be  the  means  of  distributing  the  disease. 

VITALITY    OF    PATHOGENIC   BACTERIA   IN   WATER. 

222,  Conditions  Affecting  Vitality, — While  common  experience  has 
for  centuries  associated  certain  diseases  with  impure  or  polluted  water- 
supplies,  it  has  not  been  possible  until  the  methods  of  bacterial  inves- 
tigation  were   employed    to   determine  just   how   long  a  water  once 
rendered    impure    through    fecal    or    other    pollution    would    remain 
dangerous    to    human    health.       Since    the    discovery  of  the    specific 
organisms  that  are  the  inciting  cause  of  different  diseases,  and  the  study 
of  them  under  varying  conditions  in  waters  of  diverse  sources,  as  to 
how   long  such  organisms  are  able  to  retain  their  vitality  in  natural 
waters,  it  has   become   possible  to   limit  much   more  accurately  this 
period  of  danger. 

It  is  very  important  to  recognize: 

(1)  Whether  pathogenic  bacteria  once  introduced  into  water  are 
able  to  multiply  therein ;  and, 

(2)  Supposing-  that  conditions  do  not  favor  their  growth,  how  long 
such  pathogenic  bacteria  are  able  to  retain  their  vitality  and  virulence. 

Having  once  determined  these  conditions,  it  then  becomes  possible 
to  state  with  some  degree  of  accuracy  the  period  during  which  water 
polluted  with  such  germ-life  is  dangerous. 

Any  satisfactory  answer  to  these  propositions  must  take  into  con- 
sideration a  number  of  conditions,  both  as  to  the  organism  and  the 
influence  of  its  environment,  that  will  exert  a  varying  effect  on  the 
vitality  of  any  germ.  The  more  prominent  of  these  factors  are  as 
follows : 

Natural  variation  in  the  organism  itself,  due  to  age,  condition  of 
culture,  and  previous  history  of  the  same ;  the  number  of  disease  germs 
present  in  the  water;  the  condition  of  the  water  as  a  growth  medium 
as  to  its  composition,  the  amount  of  organic  matter,  the  nature  of  the 
same,  whether  it  is  suspended  or  soluble,  the  presence  of  by-products 


200  COMMUNICABLE  DISEASES  AND    WAITER-SUPPLIES. 

of  previous  bacterial  growth,  the  chemical  reaction  of  the  water  itself; 
the  effect  of  varying  conditions  in  environment  as  to  the  temperature 
of  the  water,  the  amount  of  oxygen  dissolved,  the  effect  of  light,  and 
the  state  of  water  as  to  motion. 

All  of  these  factors  exert  more  or  less  effect  on  the  vitality  of 
bacteria,  and  particularly  on  that  of  disease-producing  microbes.  In- 
asmuch as  these  conditions  are  not  constant  in  all  waters,  it  naturally 
follows  that  any  specific  organism  will  be  subject  to  a  good  deal  of  varia- 
tion in  the  length  of  time  it  will  remain  in  a  living  condition  in  water. 
It  is  therefore  not  so  surprising  to  find  considerable  difference  in  experi- 
mental results,  which  fact  should  lead  to  caution  in  deducing  definite 
laws  as  to  this  question. 

223,  Vitality  of  Typhoid  Organism, — The  closer  relation  of  typhoid 
fever  to  polluted  water-supplies  renders  a  determination  of  the  vitality 
of  this  germ  of  more  than  ordinary  importance.  Although  the  typhoid- 
fever  bacillus  is  not  a  spore-bearing  form,  nevertheless  it  is  able  to 
retain  its  vitality  in  drinking-waters  for  'a  considerable  period  of  time, 
as  is  evidenced  by  the  numerous  outbreaks  traceable  to  infected 
supplies. 

Under  ordinary  conditions,  from  the  direct  experiments  already 
made,  it  seems  improbable  that  there  is  any  considerable  growth  of  the 
typhoid  bacillus  in  potable  waters,  although,  as  Frankland  *  has  shown, 
it  is  possible  to  acclimate  the  organism  to  such  a  dilute  food-medium 
that  it  will  actually  grow  in  surface-waters ;  but  under  the  circumstances 
in  which  it  would  naturally  find  its  way  into  potable  supplies  there 
would  be  but  scant  opportunity  for  this  acclimation  process  to  occur. 
Where  organic  matter  is  present  that  is  available  as  a  food-supply,  as 
in  sewage-polluted  waters,  cell-multiplication  may  be  possible, t  but 
even  here  there  are  other  retarding  factors,  such  as  the  effect  of 
bacterial  by-products,  that  tend  to  prevent  growth. 

In  order  to  determine  the  period  through  which  the  organism  is 
able  to  survive  in  water,  a  large  amount  of  data  has  been  collected. 
The  results,  however,  are  so  conflicting  that  it  is  impossible  to  closely 
define  these  limits. 

Of  the  earlier  work,  Frankland' s  seems  to  have  been  most  closely 
controlled.  He  studied  the  longevity  of  typhoid  in  polluted  Thames 
water,  a  soft  peaty  water  (Loch  Katrine)  and  a  hard,  deep  well  water. 
Tests  were  made  in  raw,  sterilized  and  filtered  samples.  The  results 
obtained  with  sterilized  and  filtered  are,  of  course,  inapplicable  to  normal 

*  Zeitf.  Hyg.  1895,  xxi.  p.  406. 

t  Olivier.     Comp.  rend.  d.  sc.  Soc.  de  BioL,  1889,  No.  27. 


VITALITY  OF  PATHOGENIC  BACTERIA    IN   WATER.  2OI 

conditions,  but  the  prolonged  vitality  of  the  organism  in  all  cases  (20-5 1 
days  in  sterilized  and  1 1-39  days  in  filtered)  compared  with  the  effect  in 
raw  (9-33  days)  indicates  that  the  longevity  of  the  organism  is  less  in  raw 
waters  than  in  sterile  waters.  In  this  series  the  typhoid  organism  disap- 
peared much  more  rapidly  in  surface  waters  than  in  unpolluted  well  waters. 

All  experimental  work  on  the  vitality  of  organisms  carried  on  in 
glass  containers  is  subject  to  a  factor  of  error  due  to  the  protective 
action  of  the  glass  vessel  on  the  organism  as  shown  by  Picker. 

Jordan,  Zeit  and  Russell  *  have  carried  on,  simultaneously  but  inde- 
pendently, a  most  extensive  series  of  experiments  on  the  influence  of 
the  waters  of  Lake  Michigan  and  Illinois  River  on  the  vitality  of 
typhoid.  To  avoid  influence  of  glass  containers,  their  experiments 
were  made  in  diffusible  membranes,  as  parchment  and  celloidin.  Sacs 
made  of  this  material  and  filled  with  respective  types  of  waters  (Lake 
Michigan,  sewage  from  Chicago  Drainage  Canal,  and  Illinois  River)  were 
inoculated  with  freshly  isolated  typhoid  organisms  and  immersed  in 
these  respective  waters.  The  typhoid  organism  was  recovered  from 
these  water  samples  by  various  differential  culture  methods,  and  in 
every  case  the  presumptive  cultures  were  crucially  tested  by  the 
agglutination  (Widal)  test.  The  results  uniformly  indicated  that  the 
exposures  in  the  sewage  and  sewage  polluted  river  water  resulted  in  the 
destruction  of  the  typhoid  more  rapidly  (3  days)  than  in  Lake  Michigan 
water  (about  7  days). 

Russell  and  Fuller  f  continued  these  investigations,  using  Lake 
Mendota  water  and  dilute  fresh  sewage.  They  studied  the  permeability 
of  the  containing  sacs,  introducing  still  another  type,  agar  membranes, 
and  their  results  substantially  confirmed  those  previously  referred  to. 
It  is  apparent  from  these  investigations  that  the  forces  which  result  in 
the  destruction  of  the  typhoid  organism  operate  much  more  rapidly  in 
highly  polluted  than  pure  waters. 

In  solving  so  important  a  question  as  this,  it  is,  of  course,  well  to 
weigh  carefully  all  possible  sorts  of  evidence.  As  supplementing  the 
experimental  findings,  epidemiological  evidence  would  be  of  great  value, 
where  towns  using  the  same  stream  for  sewage  disposal  and  water  sup- 
ply might  have  successive  epidemics  of  this  disease.  Such  findings, 
however,  are  not  frequent. 

The  evidence  is  practically  unanimous  that  this  organism  persists 
longer  in  cold  waters  than  in  those  of  summer  temperature.  At 
Lawrence  the  rate  of  decrease  was  noted  as  follows  when  the  typhoid 

*  Journ.  Inf.  Diseases,  1904, 1.  p.  641.     t  Journ.  Inf.  Diseases,  Supp.  No.  2,  Feb.,  1906. 


2O2  COMMUNICABLE  DISEASES  AND    WATER-SUPPLIES. 

bacillus  was  exposed  in  Merrimack  River  water  kept  near  the  freezing- 
point. 

Day  of  analysis I  5  10  15          20         25 

Number  per  c.c 6120        3100        490        100        17          o 

The  spread  of  the  disease  from  Lowell  to  Lawrence  during  the 
winter,  and  the  Plymouth,  Pa.,  case  in  which  typhoid  dejecta  were 
exposed  in  the  snow  from  January  to  March  to  a  minimum  tempera- 
ture of  —  22°  F.,  indicate  that  low  temperatures  are  certainly  ineffective 
agents  in  the  destruction  of  this  organism. 

224.  Cholera. — In    the    experimental    results    obtained    as    to    the 
vitality  of  the  cholera  spirillum  in  natural  waters,  the  data  are  even 
more  conflicting  than  with  typhoid.      In  order  to  encourage  growth, 
Bolton  *  found  that  about  400  parts  of  organic  matter  per  1 ,000,000  were 
necessary.     This  explains  why  the  germ  lives  longer  in  a  polluted  than 
in  a  pure  water.      Trenkmann  t  has  determined  that  the  vitality  of  the 
cholera   spirillum   is   considerably   prolonged  where    the    organism  is 
grown   in   solutions   containing   sodium   chloride.      This  is  of  interest 
as  explaining  the  presence  of  the  organism  in  brackish  waters  (river 
Elbe  at  Hamburg,:):  harbor  at  Marseilles). 

In  general,  the  experimental  results  indicate  that  the  cholera  spiril- 
lum is  unable  to  retain  its  vitality  in  potable  waters  for  as  long  a  time 
as  the  typhoid  bacillus.  In  the  majority  of  experiments  cited,  the 
duration  of  vitality  was  only  1-3  days.  On  the  other  hand,  some 
reputable  observers  claim  to  have  found  it  in  ordinary  water  several 
months  after  infection.  In  Cologne  sewage  Stutzer  and  Burri  §  found 
it  lived  from  7-13  days. 

At  low  temperatures  it  retains  its  ability  to  grow,  as  has  been 
determined  experimentally,  as  well  as  empirically  in  the  winter 
epidemics  that  occurred  at  Nietleben  and  Altona  in  1893.!! 

Owing  to  the  fact  that  the  period  of  incubation  with  this  disease  is 
quite  short  (i-$  days),  it  is  more  often  possible  to  detect  the  presence 
of  this  organism  in  polluted  supplies  than  it  is  with  typhoid.  (See 
Literature  of  this  chapter.)  For  such  determinations  the  differential 
media  that  have  been  devised  may  be  successfully  used  (149). 

225.  Anthrax. — The  problems  presented  in  the  case  of  this  disease 
organism  differ  materially  from  those  previously  noted,  in  that  Bacillus 

*  Zeit.f.  Hyg.y\.  p.  i. 
f  Cent.  f.  Bakt.,  1893,  xm.  p.  313. 

%  The  chlorine  content  of  river  is  greatly  increased  by  the  waste  waters  from  the 
Stassfurt  salt-works  (See  Aufrecht,  Cent.  f.  Bakt.,  1893,  xni.  p.  353.) 
§  Hyg.  Rund.,  IV.  p.  208. 
|  Koch.     Zeit.f.  Hyg.,  1893,  xiv.  p.  393. 


CONCLUSION.  203 

ant /tracts  is  able  to  form  spores,  and  hence  is  much  more  resistant. 
Spores,  however,  are  only  produced  in  contact  with  air  and  where  the 
temperature  is  at  least  60°  F. 

There  is  little  probability  of  the  pollution  of  waters  by  anthrax  from 
human  sources,  but  it  not  infrequently  happens  that  this  disease  organism 
finds  its  way  into  water  from  animal  sources,  and  inasmuch  as  the  same 
germ  is  able  to  produce  anthrax  in  both  man  and  animals,  the  origin 
of  the  same  is  a  matter  of  no  little  moment.  Tanneries,  brush- 
factories,  etc.,  are  particularly  liable  to  distribute  the  disease  germ  by 
the  way  of  the  water,  owing  to  the  fact  that  hides,  hair,  and  wool  are 
frequently  infected.  In  such  cases  the  disease  germ  is  more  apt  to  be 
in  the  spore  rather  than  the  vegetative  form  and  therefore  will  be  much 
more  resistant. 

In  the  sporeless  stage  the  organism  is  able  to  live  but  for  a  short 
time.  Two  to  five  days  mark  the  ordinary  limits  of  existence  in  sur- 
face-waters, the  organism  degenerating  more  rapidly  in  summer  than 
in  winter.  Under  summer  conditions  the  germ  may  sporulate,  in 
which  condition  it  is  able  to  live  over  from  one  year  to  the  next.  In 
lowlands  subject  to  overflow,  the  conditions  seem  to  be  the  best  for  the 
perpetuation  of  the  vitality  of  the  organism. 

226,  Conclusion. — Experimental  tests  have  been  made  with  other 
kinds  of  pathogenic  bacteria,  but  the  results  are  only  of  general  scientific 
interest.  In  summarizing,  all  bacteria  of  disease  are  killed  out  sooner 
or  later  in  waters.  Ordinarily  the  amount  of  organic  nutriment  con- 
tained in  water  is  not  sufficient  to  encourage  rapid  development,  and 
the  consequence  is  that  most  forms  are  sooner  or  later  starved  out. 

LITERATURE. 

A  large  amount  of  literature  showing  the  relation  of  communicable  dis- 
eases to  water-supplies  is  in  existence,  but  for  the  most  part  it  is  widely  scat- 
tered in  various  hygienic,  bacteriological,  engineering,  and  other  journals, 
In  a  few  such  works,  as 

Hill's  Public  Water-supplies, 

Fuertes'  Water  and  Public  Health, 

Abbott's  Hygiene  of  Transmissible  Diseases, 

Sedgwick's  Principles  of  Science  and  Public  Health,  and 

Whipple's  Typhoid  Fever, 

some  of  the  more  classic  examples  are  given.  Typhoid  epidemics  may  be 
classified  according  to  their  respective  vehicles  of  transmission  as  due  to 

(1)  Water-supplies. 

(2)  Milk-supplies. 

(3)  Food  (shell  fish,  oysters,  etc.) 


204  COMMUNICABLE  DISEASES  AND   WATER-SUPPLIES. 

while  more  recently  flies  have  been  shown  to  be  actively  associated  with  the 
distribution  of  infected  material,  as  in  the  typhoid  fever  outbreaks  in  the 
military  camps  during  the  Spanish- American  war,  yet  the  larger  percentage 
of  epidemics  of  typhoid  fever  are  caused  by  infection  in  various  ways  of 
water-supplies.  See  Schiider,  Zeit.  f.  Hyg.,  1901,  xxxvm.  p.  343,  in  which 
there  is  collected  literature  relating  to  650  typhoid  epidemics. 


TYPHOID. 

1.  Epidemics   arising  from   Infected  Ground  Water-supplies,  (springs   or 
wells)  are  usually  more  or  less  circumscribed  in  their  distribution      Charac- 
teristic epidemics  are  noted  in  the 

Wittenberg,  Germany,  outbreak,  which  was  due  to  infection  of  a  well  sup- 
plying garrison.  (See  Gaffky.  Mitt.  a.  d.  kais.  Gesundheitsamte,  1884,  n. 
p.  410.) 

Lausanne,  Switzerland,  1872.  Infection  of  town  supply  (spring)  through 
imperfect  filtration  of  soil. 

Deutsche  Arch.  f.  klin.  Med.  1893,  Band  xi. 

2.  Epidemics  caused  by  Accidental  Infection  of  a  Satisfactory  Supply. 
Baraboo,  Wisconsin,  infection  of  a  pure  supply  from  wells  by  passage  of 

distributing  pipes  through  polluted  water.  (See  Kirchoffer,  W.  G.,  Eng. 
News,  Nov.  27,  1902  ;  also  Russell,  H.  L.  Report  Wisconsin  State  Board 
of  Health.  1903.) 

Butler,  Pa.  Infection  of  filtered  supply  due  to  temporary  discontinuance 
of  filter  operations.  Soper,  G.  A.,  Eng.  News,  Dec.  24,  1903. 

3.  Epidemics  caused  by  Contamination  of  Supplies  of  Surface  Origin. 
Ithaca,  N.  Y.  (See  Soper,  G.  A.,  Jour.  N.  E.  W.  W.   Assn.,  December, 

1904.) 

Plymouth,  Pa.,  1885.  One-ninth  of  entire  population  of  9,000  stricken 
with  disease  due  to  pollution  of  open  public  reservoir  with  fecal  discharges 
from  single  typhoid  case.  (See  Sedgwick,  Principles  of  Sanitary  Science, 
p.  200.) 

Pittsburg,  Allegheny  and  vicinity,  Eng.  News,Feb.  25,  1904. 

Philadelphia,  Pa.,  Annual  Report,  Dept.  Public  Safety  of  Phila.,  1898. 

Lowell-Lawrence,  Mass.,  24th  Report  Mass.  Board  of  Health,  1892. 

Washington,  D.  C.,  Eng.  News,  Nov.  8,  1906. 

4.  Epidemics  due  to  Infection  of  Milk-supplies. 

For  most  complete  recent  resume,  see  Milk  and  Its  Relation  to  Public 
Health,  Bulletin  41,  Hygienic  Laboratory,  Public  Health  and  Marine  Hos- 
pital Service  of  the  U.  S.,  1908. 

Stamford,  Conn.,  1895.  Three  hundred  and  eighty-six  cases  developed 
within  six  weeks,  of  which  97  per  cent  came  from  a  single  milk  supply,  milk 
being  infected  by  rinsing  out  the  cans  with  cold  water  from  a  shallow  con- 
taminated well.  (See  Smith,  H.  E.,  Conn.  State  Board  of  Health  Report, 
1895,  p.  161.) 

Montclair,  N.  /.,  9th  Annual  Report  Montclair  Board  of  Health,  1903. 

Palo  Alto,  Cal.  Of  900  people  supplied  with  milk  from  one  dairy  232 
had  typhoid  fever.  (See  Modern  Medicine,  Osier,  Vol.  II.  p.  85.) 

Springfield  and  Somerville,  Mass.,  24th  Report  Mass.  Board  of  Health, 
1892,  p.  715. 


LITERATURE.  2O$ 

CHOLERA. 

Hamburg- Altona,  Germany,  1892.     The  most  striking  case  on  record  of 
the  value  of  sand  filters  in  checking  disease  outbreaks. 

Koch.  Wasserfiltration  und  Cholera.  Zeit.  f.  Hyg.,  1893,  xiv.  p.  393  , 
also  ibid.,  xv.  p.  89. 

Reincke.     Ber.  d.  medic.  Inspect,  d.  Hamburg.     Staates  f.  1892,  p.  28. 

Gaffky.     Arb.  a.  d.  kais.     Gesundheitsamte,  x.  pp.  1-129. 
Cholera  in  Germany  other  than  In  Hamburg  in  1892-93. 

Arb.  a.  d.  kais.     Gesundheitsamte,  x.  pp.  129-273. 

Korber.     Dorpat  outbreak.     Zeit.  f.  Hyg.,  1895,  xix.  p.  161. 

Koch.     Nietleben  outbreak.     Zeit.  f.  Hyg.,  1894,  xv.  p.  123. 
Cholera  in  Germany  in  1894. 

Arb.  a.  d.  kais.     Gesundheitsamte,  xn.  pp.  1-285. 

DIARRHOEAL  EPIDEMICS. 

Hamburg-Altona,  1880,  1888,  1892. 

Reincke.     Ber.  d.  med.  Inspect,  d.  Hamburg.    Staates  fur  1892,  p.  10. 

Bockendahl.  Generalber.  ii.  d.  offentl.  Gesundheitswesen  fur  Schl. 
Hoi.,  1870,  p.  io. 

(Abstracts,  of  both  of  these  articles  in  Hazen's  Filt.  Pub.  Water- 
supplies,  p.  226.) 


PART  II. 
THE  CONSTRUCTION  OF  WATER-WORKS. 


CHAPTER  XI. 

GENERALITIES   PERTAINING   TO   WATER-WORKS 
CONSTRUCTION. 

227,  In  the  preceding  chapters  there  have  been  discussed  the 
various  matters  relating  to  the  requirements  of  a  water-supply  and  the 
capabilities  of  the  various  sources  as  regards  quantity  and  quality.  In 
the  remaining  portions  of  this  work  there  will  be  considered  in  detail 
the  design  and  construction  of  the  various  parts  entering  into  a  system 
of  water-works. 

Questions  of  quantity  and  quality  are  of  prime  importance  in  the 
selection  of  a  source  of  supply,  but  that  the  solution  may  be  the  best  it 
is  also  necessary  to  consider  the  question  of  cost,  a  matter  which 
depends  upon  the  extent  and  character  of  the  various  parts  of 
the  works  involved.  With  two  or  more  sources  at  hand,  each  of  which 
will  furnish  water  of  sufficient  quantity  and  equally  good  quality,  the 
problem  resolves  itself  into  one  of  economy  as  measured  by  the  first 
cost  plus  the  capitalized  cost  of  operation.  The  problem  is,  however, 
rarely  so  simple  as  this,  questions  of  future  enlargement,  differences  in 
quality,  possible  future  pollution,  and  financial  resources  of  the  com- 
munity being  some  of  the  elements  which  render  the  question  a  com- 
plicated one.  Thus  a  complete  general  knowledge  of  the  problem 
becomes  a  prerequisite  to  an  intelligent  selection  of  source  as  well  as 
to  the  actual  construction  of  the  works. 

Before  passing  on  to  the  details  of  water-works  construction  it  will 
be  of  assistance  to  get  a  general  view  of  the  subject,  and  to  that  end 
we  will  here  briefly  describe  the  various  general  features,  the  arrange- 

206 


GENERAL  ARRANGEMENT  OF   WATER-WORKS.  2O/ 

ment  of  the  various  parts  of  a  system,  and  the  standards  by  which  the 
economy  of  various  methods  and  arrangements  can  be  compared. 

GENERAL   ARRANGEMENT   OF   WATER-WORKS. 

228.  Classification. — The  various  constructive  features  of  a  water- 
supply  system  are  divided  into  three  groups:   (i)  Works  for  the  collec- 
tion of  water;    (2)  Works  for  the  purification  of  water;   (3)  Works  for 
the  conveyance  and  distribution  of  water. 

229.  Works  for  the  Collection  of  Water. — These  are  divided  according 
to  the  nature  of  the  source  into:  (A)  Works  for  taking  water  from  large 
streams  and  natural  lakes;    (B)  Works  for  the  collection  of  ground- 
water;    (C)  Works  for  the  collection  of  water  from  small  streams  by 
means  of  impounding  reservoirs. 

A.  Works  for  taking  water  from  large  streams  or  lakes  vary  in 
character  from  a  simple  cast-iron  pipe  extending  a  short  distance  from 
shore,  to  the  expensive  tunnels  and  cribs  of  some  of  the  large  cities  on 
the  Great  Lakes.      The  location   of  these  works  is  determined  very 
largely  with  respect  to  the  quality  of  the  water  obtainable.     Wherever, 
as  is  often  the  case,  it  is  desired  to  draw  a  supply  from  a  lake  which 
at  the  same  time  receives  sewage  from  the  city,  the  question  is  one 
involving  great  difficulties. 

B.  Works   for  the   collection   of  ground-water  consist  of  various 
forms    of    shallow    wells,    artesian    wells,    filter-galleries,    etc.       The 
location  of  works  of  this  class  is  determined,  primarily,  by  the  location 
of  the  water-bearing  strata.      If  these  are  extensive,  it  will  usually  be 
convenient  and  economical  to  place  the  wells  at  relatively  low  eleva- 
tions in  order  that  the  water  may  be  readily  reached  by  pumps,  or 
perhaps  in  order  that  a  flowing  well  may  be  secured.      In  the  case  of 
shallow  wells  the  location  is  often  affected  by  the  possibility  of  local 
contamination,  an  element  usually  absent  in  the  case  of  deep  wells. 

C.  Water  collected  in  impounding  reservoirs  from  streams  of  com- 
paratively small  watersheds  depends  for  its  good  quality  chiefly  upon 
the   scarcity  of  population   upon  the  watershed.      Suitable  areas  are 
therefore  more  likely  to  be   found  in  the  more  rugged   parts  of  the 
country  and  at  the  higher  elevations,  and  usually  at  considerable  dis- 
tances, sometimes  as  great  as  50  or  75  miles,  from  the  population  to 
be  served.      The  location  of  such  impounding  reservoirs  is  also  largely 
dependent  upon  questions  of  construction,  such  as  the  location  of  the 
dam,  length  and  cost  of  aqueduct  or  conduit,  and,  what  is  of  great 
economic  importance,  whether  the  water  can  be  conveyed  and  dis- 
tributed entirely  or  partly  by  gravity. 


208  WATER-WORKS   CONSTRUCTION1  IN  GENERAL. 

230.  Works  for  the   Purification   of  Water. — These  vary  in   kind 
according  to  the  nature  of  the  impurities  to  be  removed.      Thus  in  the 
case  of  surface-waters  the  sediment,  bacteria,  etc.,  are  removed  more 
or  less  completely  by  settling-basins  and  various  forms  of  filters;  dis- 
agreeable gases  by  aeration.      In  the  case  of  ground-waters  iron  may 
be  removed  by  aeration  and  filtration ;  hardness  by  chemical  precipita- 
tion,  etc.      In  these  ways  waters   otherwise  very  undesirable  can   be 
greatly  improved  or  made  entirely  satisfactory,  but  of  course  at  a  con- 
siderable expenditure  of  money.      It  will  often  happen,  therefore,  that 
a  source  of  good  quality  but  expensive  will  need  to  be  compared  with 
another  poor  in  quality  but  capable  of  being  made  fairly  comparable 
with  the  other  at  no  greater  total  cost.     Not  infrequently  the  possibility 
of  the    future  deterioration  of  a   surface   supply   and   the   consequent 
necessity  for  artificial  purification  must  also  be  considered. 

231.  Works  for  the  Distribution  of  Water. — These  include  aqueducts 
and  conduits  for  conveying  water  from  a  distant  source,   pumps   and 
pumping-stations,  local  reservoirs  for  equalizing  the  flow  or  for  storage, 
and  the  pipes  for  distributing  to  the  consumers.     Conduits  may  be  open 
channels,   masonry  conduits    not    under  pressure,    or   closed  pressure 
conduits,  such  as  pipes  of  wood,  iron,  or  steel,  and  sometimes  tunnels. 
The  form    is   determined    chiefly  by  considerations    of  cost.      Pumps 
are  used  in  a  great  variety  of  forms  and  situations,  and  may  be  operated 
by  steam,   gas,   electricity,  wind,   or  by  hydraulic  power.      There  are 
deep-well  pumps  for  drawing  water  from  depths  not  reached  by  suction, 
low-lift  pumps  for  raising  water  from  a  river  into  settling-basins  or  on 
to  filters,  or  from  wells  into  a  low  reservoir;  and  high-lift  pumps  for 
forcing  the  main  supply  into  the  distributing  pipes  or  into  an  elevated 
distributing  reservoir.      Local  reservoirs  are  used  for  receiving  water 
from  long  conduits  and  regulating  the  flow  in  the  distributing  system, 
for  equalizing  the  flow  and  pressure  in  pumping  systems,  and  as  settling- 
reservoirs.     The  pipe  system  includes  "distributing  mains,  fire-hydrants, 
service-pipes,  shut-off  valves,  regulating- valves,  etc. 

232.  Arrangement  of  Works, — The  arrangement,  extent,   and  cost 
of  the  various  features  of  a  water-works  system  depend   greatly  upon 
the  nature  of  the  source,  its  distance  from  the  district  to  be  served,  and 
its  elevation  above  that  district. 

In  describing  the  various  _  arrangements  of  water- works  systems  it 
will  be  convenient  to  consider  them  in  two  classes:  first,  those  draw- 
ing from  a  distant  source;  and  second,  those  drawing  from  a  near-by 
source. 

Where  the  water  is  obtained  from  a  distant  source  we  may  have: 


SYSTEMS   OF  OPERATION.  2O9 

(a)  gravity  systems  in  which  water  from  an  impounding  reservoir  or 
lake  (rarely  from  other  sources)  is  led  into  a  conduit  through  which  it 
flows  down  to  the  city;  or  (U)  systems  in  which  the  water  is  pumped 
from  ground-water  sources,  or  from  rivers  or  lakes,  by  low-lift  pumps 
into  a  gravity  conduit,  or  by  high-lift  pumps  directly  into  a  pressure 
Conduit  to  the  city.  At  the  city  it  passes  into  a  small  reservoir  and  thence 
by  gravity  to  the  consumer,  or  it  may  be  pumped  from  the  reservoir 
to  a  higher  level  in  order  to  get  the  necessary  pressure  for  distribution. 
Where  the  differences  of  elevation  in  the  city  are  great  it  may  be 
economical  to  have  two  or  more  zones  of  distribution.  If  the  water  is 
to  be  purified,  the  necessary  works  may  be  located  at  any  convenient 
point  between  the  source  and  the  city.  If  placed  at  the  source,  a  set 
of  low-lift  pumps  will  probably  need  to  be  established ;  if  at  any  other 
point  along  the  conduit,  such  pumps  will  seldom  be  required. 

A  near-by  source  is  usually  at  so  slight  an  elevation  above  the  city 
that  high-lift  pumps  are  required  to  furnish  the  necessary  pressure  for 
distribution.  With  a  ground-water  source  a  set  of  low-lift  pumps  may 
often  be  used  to  elevate  the  water  into  a  low  equalizing  reservoir, 
whence  it  is  drawn  by  the  high-lift  pumps.  If  the  source  is  a  lake  or 
large  stream  and  filters  are  used,  low-lift  pumps  will  usually  be  required 
to  pump  the  water  upon  the  filters,  although  gravity  may  sometimes  be 
used  for  this.  If  the  source  is  an  impounding  reservoir,  it  is  occasionally 
at  so  high  a  level  that  a  gravity  system 'may  be  employed. 

The  most  expensive  arrangement  is  in  general  a  distant  source  at 
a  low  elevation  where  purification  is  required,  such  as  an  impure  water 
brought  from  a  distance.  The  cheapest  is  a  near-by  source  of  pure 
water  at  a  high  elevation,  such  as  a  spring- water  or  artesian  water 
under  pressure.  In  the  nature  of  things,  comparisons  between  such 
sources  will  seldom  need  to  be  made.  Systems  requiring  careful  com- 
parison are  usually  various  near-by  sources  requiring  pumping  and 
possibly  purification  with  various  remote  sources  of  pure  water  usually 
located  at  a  high  elevation. 

233,  Systems  of  Operation. — According  to  the  arrangement  of  the 
works  there  are  several  so-called  "  systems  "  of  distribution:  (i)  by 
gravity;  (2)  by  pumping  to  reservoir;  (3)  by  pumping  to  stand-pipe  or 
tank;  and  (4)  by  pumping  direct.  In  (i)  the  water  is  conveyed 
entirely  by  gravity.  In  (2)  it  is  elevated  to  a  distributing-reservoir, 
whence  it  flows  by  gravity  into  the  pipe  system.  In  (3)  a  small  stand- 
pipe  or  tank  is  substituted  for  the  reservoir,  while  in  (4)  the  water  is 
pumped  directly  into  the  mains.  In  all  these  methods  the  pipe  system 
remains  essentially  the  same. 


210 


WATER-WORKS   CONSTRUCTION  IN  GENERAL. 


In  many  cases  a  reservoir  or  standpipe  is  so  arranged  that  it 
receives  only  the  surplus  water  when  the  rate  of  pumping  exceeds  the 
demand,  and  returns  this  surplus  at  times  when  the  demand  exceeds 
the  rate  of  pumping.  This  may  be  considered  a  combination  of  (2) 
and  (4)  or  (3)  and  (4),  and  is  sometimes  called  the  direct-indirect 
system.  Again,  it  is  often  desirable  in  the  case  of  a  reservoir  or  stand- 
pipe  system  to  so  arrange  the  piping  that  in  case  of  fire  the  reservoir 
may  be  shut  off  and  an  increased  pressure  furnished  directly  by  the 
pumps. 

The  number  of  works  in  the  United  States  operated  under  the 
various  systems  are  given  in  Table  No.  34,  compiled  by  Flynn.* 

TABLE   NO.  34. 

NUMBER    OF   CITIES    AND   TOWNS    IN   THE   UNITED    STATES    SUPPLIED   WITH   WATER 
BY   THE   VARIOUS    SYSTEMS    NAMED. 


System. 

Northeastern 
States. 

Southeastern 
States. 

1 

G 
u 

ug 
5rt 

Sc/5 

Western 
States. 

3 

£ 

4QO 

4.1 

II 

104 

7-^6 

Gravity  and  pumping  : 

62 

2 

I  e 

86 

08 

I 

2 

Tq 

C/l 

II 

2 

2 

c 

20 

I 

o 

o 

I 

2 

I 

I 

g 

o 

o 

8 

12 

Total 

I  IQ 

II 

ja 

182 

Pumping  : 

74 

qq 

221 

QO 

di8 

128 

62 

7Q 

1  14 

181 

2JK 

iqO 

218 

«8 

060 

26 

II 

14. 

20 

71 

q-i 

II 

27 

AC 

116 

41 

2O 

lie 

i8s 

^61 

q 

2 

18 

IO 

qq 

CCQ 

278 

602 

822 

2342 

o 

2 

IO 

21 

II  ^Q 

qqO 

714. 

1069 

^28l 

234,  Comparison  of  the  Various  Systems.  —  In  comparing  these 
various  systems,  their  relative  advantages  and  disadvantages  should  be 
considered  in  three  respects:  safety  or  reliability  of  operation,  economy, 
and  convenience.  The  first  element  is  the  most  important,  particularly 


*  Eng.  News,  1898,  XL.  p.  10. 


SYSTEMS   OF  OPERATION.  211 

for  large  cities ;  for  in  such  a  case  the  entire  community  depends  so 
absolutely  upon  the  maintenance  of  the  public  water-supply  that  a 
failure  for  even  a  day  would  be  a  calamity.  In  smaller  cities  and 
towns  it  would  be  of  much  less  importance,  but  yet  a  very  vital  factor 
in  determining  the  value  of  a  water-supply  to  the  community.  This 
element  of  safety  cannot  readily  be  measured  in  dollars  and  cents,  but 
the  experience  of  many  places  having  an  imperfect  plant,  and  the  losses 
resulting  therefrom,  show  that  it  is  a  matter  justifying  a  large  measure 
of  consideration. 

In  the  matter  of  economy,  differences  are  more  readily  measured. 
In  comparing  the  convenience  of  two  systems  we  should  consider  the 
amount  and  uniformity  of  pressure  in  the  two  cases,  convenience  in  the 
operation  of  pumps  and  in  the  making  of  repairs  and  renewals,  use  of 
hose  versus  fire-engines,  etc.  All  of  these  involve  more  or  less  also 
the  question  of  economy. 

235,  Safety. — In  respect  to  safety  or  reliability  of  operation  the 
gravity  system  undoubtedly  ranks  first.  The  nature  of  the  structures  is 
such  as  to  render  them  little  liable  to  accident,  and  if  a  reservoir  of 
from  5  to  10  days'  capacity  is  provided  to  receive  and  distribute  the 
water  from  the  conduit,  thus  allowing  time  for  repairs,  or  if  the  conduit 
is  in  duplicate  or  of  masonry  underground,  this  system  is  exceedingly 
safe  and  reliable. 

Next  to  the  gravity  system  in  point  of  safety  is  the  system  of 
pumping  to  an  elevated  distributing-reservoir  holding  several  days' 
supply.  If  at  the  same  time  considerable  reserve  pumping  capacity  is 
furnished  to  enable  ordinary  repairs  to  be  made  without  drawing  largely 
from  the  reservoir,  this  system  is  not  far  inferior  to  the  gravity  system. 
Certain  rare  though  possible  contingencies,  such  as  a  shortage  of  fuel 
or  a  boiler  explosion,  must,  however,  be  considered  as  tending  to  place 
this  system  second  in  point  of  safety.  Hydraulic  power  is  in  this 
respect  more  reliable  than  steam-power. 

Many  water-works  have  in  place  of  a  reservoir  a  small  tank  or 
stand-pipe  holding  at  most  but  a  few  hours'  supply,  dependence  being 
placed  entirely  upon  the  pumps  for  any  continued  excessive  draught. 
This  arrangement  is  manifestly  inferior  to  the  second  system,  and  should 
not  be  used  if  a  suitable  site  can  be  found  for  an  elevated  reservoir.  In 
many  places  where  the  stand-pipe  or  the  direct-pressure  system  has 
been  in  use,  elevated  reservoirs  have  subsequently  been  constructed. 

The  system  of  direct  pumping  depends  for  its  efficiency  entirely  upon 
the  ability  of  the  pumps  to  follow  all  variations  in  consumption  and  to 
respond  at  any  instant  to  demands  for  fire  purposes.  It  ranks  last  in 


212  WATER-WORKS    CONSTRUCTION  IN  GENERAL. 

reliability,  and  should  not  be  considered  except  for  localities  of  level 
topography,  where  it  becomes  a  question  between  this  and  the  stand-pipe 
system.  For  small  or  moderate-sized  cities  an  elevated  tank  holding 
at  least  one  hour's  fire  consumption  is  an  important  element  of  safety 
and  greatly  to  be  desired.  For  large  cities  the  fire  rate  does  not  call 
for  such  a  large  relative  increase  in  pumping  capacity  and  it  can  there- 
fore be  more  readily  met  by  the  pumps.  The  total  quantity  used  is, 
moreover,  large,  and  small  tanks  would  be  of  little  value.  The  pump- 
ing machinery  in  large  works  is  also  more  likely  to  be  at  all  times  in 
good  working  condition  than  is  the  case  with  small  plants. 

Where  a  stand-pipe  is  used  for  ordinary' domestic  pressure  and 
dependence  is  chiefly  placed  on  direct  pumping  for  fire  purposes,  the 
stand-pipe  may  still  be  of  considerable  value  in  furnishing  a  fire  pressure 
suitable  for  certain  of  the  lower  districts  of  the  town  or  for  small  fires 
in  the  residence  portion. 

236.  Economy  and  Convenience. — The  relative  economy  of  different 
systems  for  a  given  city  is  a  matter  depending  entirely  upon  the  local 
conditions.  Compared  to  a  pumping  system,  the  gravity  system  is 
very  economical  of  operation,  and  the  depreciation  of  the  plant  is  also 
likely  to  be  small.  If  the  source  is  quite  remote,  the  expense  of  con- 
duit becomes  an  important  item,  and  beyond  a  certain  distance  the 
high  initial  cost  will  outweigh  the  econcfmy  of  operation.  As  a  gravity 
system  is  usually  fed  from  an  impounding-reservoir,  there  is  also 
involved  in  this  case  the  expense  of  reservoir  construction. 

Comparing  the  various  forms  of  pumping  systems,  a  large  distribut- 
ing-reservoir, while  adding  to  the  first  cost,  is  an  element  of  economy 
in  enabling  the  pumps  to  be  more  uniformly  and  economically  operated 
and  in  reducing  slightly  the  necessary  size  of  the  piping.  In  small 
works  the  pumps  can  thus  be  operated  a  convenient  number  of  hours 
each  day,  such  as  8,  10,  or  12.  A  large -reservoir  will  also  require  a 
less  amount  of  idle  pumping  capacity  for  reserve  than  either  the  direct 
or  the  stand-pipe  system.  With  respect  to  the  convenient  operation  of 
pumps  the  stand-pipe  or  tank  system  is  better  than  the  direct;  and  in 
very  small  works  it  may  effect  a  considerable  saving  by  enabling  them 
to  be  operated  for  but  a  part  of  the  time. 

As  regards  uniformity  of  pressure  the  gravity  and  reservoir  systems 
are  equally  good.  Direct  pumping  is  the  least  desirable,  but  cannot  be 
said  to  be  entirely  disadvantageous,  as  the  pressure  can  be  more  readily  * 
modified  to  suit  the  requirements.  Thus  the  high  pressure  necessary 
for  fire  extinguishment  may  be  furnished  only  so  long  as  it  is  needed, 
while  at  other  times  a  much  less  pressure  may  be  used,  a  matter  of 


THE   DUAL   SYSTEM.  213 

considerable  economical  importance.  A  similar  advantage  exists  in 
the  combined  stand-pipe  and  direct-pressure  system,  with  the  addi- 
tional one  of  a  more  flexible  operation  of  the  pumps  at  ordinary 
times. 

237.  Existing  Works  as  Affecting   Choice. — The    problems   of  the 
future  are  mostly  those  of  enlarging  and  improving  present  supplies. 
The  kind  and  condition  of  the  system  already  in  existence  will  there- 
fore often  be  of  controlling  influence  in  arriving  at  the  best  design  for 
the    new  works.      It  will   often   happen   that  the   present  source  has 
become  polluted,  and  the  question  arises  whether  it  be  best  to  abandon 
it,  to  purify  the  water,  or  to  use  the  water  for  other  than  domestic  pur- 
poses.    Combinations  may  thus  be  made  between  old  and  new  systems 
or  sources,   and  these  may  be  either  operated   together  or  independ- 
ently, each  one  serving  a  separate  district,  a  separate  zone  of  elevation, 
or  a  separate  service. 

238.  The  Dual  System. — It  has  been  proposed  that  where  it  becomes 
very   expensive  to   furnish   a  water  suitable   for  drinking   purposes,   a 
double   system  be   adopted.      One  system  would  furnish  water  of  the 
purest  quality  for  drinking  and  culinary  purposes,  while  the  other  would 
supply  water   for   other   domestic  purposes,   and   for    commercial  and 
public  use.      The  former  would  be  perhaps  relatively  expensive,  but  as 
the  quantity  required  would  be  only  5  or  6  gallons  per  head  per  day, 
the  total  expense  would  not  be  great.      It  would  also  often  be  much 
easier  to  find  a  good  water  in  the  quantities  required  for  this  purpose 
than  for  the  entire  supply.    For  example,  a  city  of  one  million  inhabit- 
ants would  require  only  5  or  6  million  gallons  per  day  of  pure  water, 
a  quantity  that  could  very  often  be  obtained  from  good  ground-water 
sources,  such  as  would  be  entirely  inadequate  to  supply  all  the  water 
required.      The  larger  quantity  could  then  be  obtained  from  cheaper 
sources,  making  the  total  expense  in  many  cases  less  than  under  the 
usual  single  system. 

The  chief  objection  to  this  double  system  is  the  fact  that  there 
would  be  in  all  houses  impure  as  well  as  pure  water,  and  unless  the. 
former  be  very  bad,  unfit  in  fact  for  washing  purposes,  many  persons 
would  be  careless  or  indifferent  as  to  its  use  and  thus  the  benefits  of  a 
pure  water  to  a  community  would  be  very  largely  neutralized.  That 
such  would  be  the  case  is  indicated  by  the  experience  at  Lawrence, 
Mass.,  where,  after  the  introduction  of  filter-beds  to  purify  the  city 
water-supply,  a  considerable  number  of  cases  of  typhoid  fever  still 
remained,  most  of  which  were  traced  to  mill  operatives  who  used  raw 
canal  water  at  the  mills,  although  city  water  was  readily  obtainable. 


214  WATER-WORKS   CONSTRUCTION  IN  GENERAL. 

A  more  practical  dual  system  would  be  one  which  would  supply  the 
purer  water  for  all  domestic  purposes,  and  the  other  and  cheaper  water 
for  certain  commercial  and  public  uses.  Such  a  system  is  in  use  in  a 
number  of  foreign  cities  with  resulting  economy.  In  Paris,  for  exam- 
ple, where  the  use  of  water  for  street  cleaning  is  so  great,  a  separate 
and  cheap  supply  is  used  for  this  purpose.  Special  high-pressure  fire 
systems  are  of  great  value  in  large  cities,  and  since  1900  such  systems 
have  been  installed  in  several  places.  See  Art.  757  for  further  data. 
The  merits  of  salt  water  for  street  sprinkling  may  make  it  advantageous 
in  towns  located  on  tide-water  to  construct  a  separate  sea-water  pipe 
system.  It  will  also  often  happen  that  a  number  of  large  commercial 
consumers  of  water  are  so  located  that  they  may  be  economically 
supplied  with  cheap  water  through  a  separate  system. 

PRINCIPLES   OF   ECONOMIC   CONSTRUCTION. 

239.  The  General  Problem. — In  fixing  upon  a  design  the  engineer 
must  constantly  keep  before  him  the  question  of  economy, — economy 
in   the  long  run  and  generally  speaking.      The  consideration  of  this 
question  always  involves  matters  relating  to  the  future  that  can  be  only 
approximately  determined,  and  on  that  account  it  is  often  very  difficult 
to  make  a  correct  decision.     Thus  the  cost  of  operation  may,  and  often 
does,  change  materially;  so  also  the  interest  rates,  and  the  cost  of 
material,  and  even  the  methods  of  construction. 

The  expense  of  any  works  to  any  community  is  made  up  of  three 
parts:  (i)  first  cost;  (2)  cost  of  operation  and  repairs;  and  (3)  depre- 
ciation, or  the  cost  of  renewals  not  included  under  ordinary  repairs. 
The  problem  of  the  engineer  as  regards  economy  is  to  secure  a  mini- 
mum sum  total  of  these  three  items  of  expense.  In  addition  he  must 
usually  consider  the  question  of  annual  payment  into  a  sinking  fund. 

240.  Methods  of  Comparing  Cost. — Different  systems  may  be  com- 
pared  as   to   economy  either  by  comparing  the  value  of  the   capital 
invested  and  required  to  keep  the  plant  in  operation,  or  by  comparing 
the   annual   expense,   including  the   depreciation  and  interest  on  the 
investment.      The  former  method  is  frequently  employed  in  comparing 
designs  of  structures  where  the  first  cost  is  of  relatively  great  importance, 
but  for  certain  purposes  it  is  important  to  look  at  the  matter  from  the 
standpoint  of  annual  charges,  especially  in  connection  with  the  financial 
management  of  the  works,  provision  for  payment  of  bonds,  etc.      Both 
methods  should  give  the  same  relative  result. 


METHODS  OF  COMPARING    COST.  21$ 

241.  Method  of  Capitalization.  —  To  correctly  state  the  cost  of  a 
works  in  terms  of  capital  we  have:  (i)  the  first  cost;  (2)  the  annual 
cost  of  operation  and  maintenance  capitalized  at  the  current  rate  of 
interest;  (3)  the  capital  which  must  be  added  to  make  good  the 
depreciation.  The  last  sum  must  be  such  an  amount  as  will,  when  put 
at  compound  interest,  provide  a  sum  at  the  expiration  of  the  life  of  the 
structure  sufficient  to  renew  it  and  also  to  leave  a  sum  equal  to  the 
original  amount  for  further  future  provision.  These  three  sums  will 
then  equal  an  amount  sufficient  to  construct,  operate,  and  perpetually 
maintain  the  plant. 

Many  parts  of  a  water-works  system  can  be  kept  in  perfect  service 
indefinitely  by  the  ordinary  repairs.  These  are  not  subject  to  depre- 
ciation. Other  parts  must  be  renewed  from  time  to  time.  What  are 
considered  as  repairs,  what  as  renewals,  and  what  as  new  improve- 
ments will  depend  upon  the  method  of  keeping  accounts  in  the  particu- 
lar water-works  considered,  but  this  detail  will  be  left  for  subsequent 
discussion  (Chapter  XXIX). 

That  part  of  the  cost  represented  by  items  (i)  and  (2)  is  readily 
stated  and  requires  no  further  comments.  The  capital  necessary 
to  provide  for  depreciation  may  be  determined  as  follows  :  Let  P  = 
sum  required;  C  =  cost  of  renewal,  assumed  equal  to  the  first  cost; 
r  =  rate  of  interest;  and  n  =  years  of  life  of  the  structure.  Then 
placing  P  at  compound  interest  we  must  have 

P(i  +  rY  =  C  +  P, 
whence 


P     : 


If  0  =  annual  cost  of  operation  and  maintenance,  we  then  have  the 
total  capitalized  sum 


In  permanent  structures  the  term  P  drops  out  and  the  problem  reduces 
to  a  comparison  of  the  first  cost  plus  the  capitalized  cost  of  operation, 

C  -\  --  ,   a  very  simple  matter.      With  structures  not  permanent  the 
term  P  must  be  considered,   and   this   requires  a  knowledge  of  the 


2l6  WATER-WORKS   CONSTRUCTION  IN  GENERAL. 

durability  of  the  various  kinds  of  structures,  and  some  judgment  as  to 
their  continued  usefulness  independent  of  their  durability. 

As  an  example  of  the  method  of  computation  of  the  total  capital 
required  suppose  that  a  certain  structure  costs  $50,000;  that  the 
operating  expenses  are  $5000  per  year,  and  that  the  life  of  the  struc- 
ture is  thirty  years.  If  money  is  worth  5  per  cent,  the  total  capitalized 
cost  will  be,  substituting  in  eq.  (2), 

5000  50,000 

.  5  =  50,000  +  -^-  +  (l>og)30_l  =  $50,000  +  $100,000  +  $15,000 

=  $165,000. 
If  this  same  structure  would  last  forty  years,  the  last  term  becomes 

—  *    '4Q    -  —  =  $8300,  and  the  total  capital  $158,300;  if  fifty  years, 

the  last  term  becomes  $5200,  and  the  total  capital  $155,200.  It  is  to 
be  noted  from  these  figures  that  to  make  the  structure  last  forty  instead 
of  thirty  years  would  justify  an  initial  expenditure  of  $15,000  —  $8300 
=  $6700  ;  to  make  it  last  fifty  years,  an  additional  expenditure  of  but 
$3100,  and  to  make  it  last  indefinitely,  only  $5200  more.  Compared 
to  first  cost  and  cost  of  operation,  it  is  thus  evident  that  the  question 
of  extending  the  life  of  a  plant  by  adding  to  the  first  cost,  when  that 
life  is  already  twenty-five  or  thirty  years,  is  a  very  minor  consideration. 
This  example  shows  also  that  no  great  accuracy  is  necessary  in  esti- 
mating the  life  of  a  plant  when  it  is  of  a  fairly  permanent  character. 

Many  other  elements  enter  in  to  modify  these  mathematical  results. 
For  example,  inconvenience  of  renewal,  and  reliability  of  operation, 
tend  greatly  to  increase  the  value  of  a  permanent  structure;  while 
future  improvements  in  methods  and  processes  tend  in  the  opposite 
direction. 

242.  Method  of  Annual  Expense,  —  The  annual  expense  will  be  equal 
to  the  interest  on  the  first  cost,  plus  the  cost  of  operation,  plus  the 
annual  depreciation.  It  is  evidently  equal  to  the  interest  on  the  total 
capitalized  cost  as  previously  found,  or  to  Cr  -\-  O  -j-  Pr.  The  last 
term  of  this  expression  may  be  called  the  annual  depreciation,  and  by 
substituting  from  eq.  (i)  we  have,  letting  D  =  annual  depreciation, 


(3) 


in  which  C  =  cost  of  renewal  (=  first  cost),  r  =  rate  of  interest,  and 
n  =  life  of  plant  in  years.      The  annual  rate  of  depreciation  per  unit  of 

COSt  =  (I  +  r)"  -  I" 


DEPRECIATION  OF  STRUCTURES. 

The  annual  depreciation  may  be  otherwise  expressed  as  the  annual 
payment  which  if  placed  at  compound  interest  will  accumulate  a  fund 
equal  to  C  at  the  end  of  n  years.  Formula  (3)  assumes  the  payment 
to  be  made  at  the  end  of  each  year.  Table  No.  35  gives  the  annual 
payment  required  to  accumulate  $1.00  at  the  end  of  various  periods  of 
time  and  at  various  rates  of  interest,  calculated  according  to  eq.  (3). 
From  this  the  annual  rate  of  depreciation  can  be  directly  determined. 
Thus  if  the  life  of  a  structure  is  estimated  at  thirty  years  and  the 
interest  rate  is  3  per  cent,  the  annual  depreciation  will  be  2. 1  per  cent 
of  the  first  cost. 

Provision  for  a  Sinking  Fund.  —  Where  bonds  are  issued  to  cover 
the  first  cost  of  a  works  it  is  usually  considered  good  policy  to  provide 
a  sinking  fund  for  the  entire  liquidation  of  the  debt  at  the  end  of  some 
long  period,  such  as  thirty  or  forty  years.  While  this  question  does 
not  strictly  enter  into  a  determination  of  the  true  economy  of  a  struc- 
ture, yet  the  matter  of  required  annual  payment  for  several  years  to 
come  is  usually  of  the  most  vital  importance  to  the  present  generation. 
To  what  extent  a  sinking  fund  should  be  considered  in  comparative 
estimates  is  not  easy  to  say.  It  depends  on  what  the  policy  of  the 
water  department  is  likely  to  be.  Probably  very  few  departments  pro- 
vide funds  to  fully  cover  depreciation,  and  also  a  sinking  fund.  The 
latter  is  indeed  likely  to  be  the  chief  consideration,  and  the  matter  of 
renewals  left  to  the  future.  In  some  cases,  especially  those  relating 
to  the  improvement  of  supplies  of  large  cities,  it  will  be  well  to  make 
full  allowance  for  both  depreciation  and  sinking  fund,  but  in  most  cases 
it  would  appear  to  be  a  fairer  basis  of  comparison  and  a  sufficient  pre- 
caution against  unforeseen  contingencies,  to  omit  the  sinking  fund  and 
to  consider  the  permanent  parts  of  the  plant  as  subject  to  a  slight 
depreciation.  If  account  is  to  be  taken  of  annual  payments  into  a  sink- 
ing fund,  the  amount  necessary  to  accumulate  any  given  sum  can  easily 
be  determined  from  Table  No.  35. 

243.  Depreciation  of  Structures.  —  The  rate  of  depreciation,  or  the 
life  of  various  parts  of  a  water-works,  is  very  various.  With  certain 
parts,  such  as  dams,  masonry  aqueducts,  and  the  like,  the  life  with 
ordinary  repairs  is  practically  indefinite.  Brick  and  stone  buildings  are 
subject  to  a  small  depreciation.  Pipes  buried  in  the  ground  have  a  life 
not  yet  well  determined  and  which  depends  much  on  the  character  of 
the  soil.  Cast  iron,  properly  coated,  appears  to  depreciate  very  slightly, 
if  at  all.  Its  life  is  variously  estimated  at  from  fifty  to  one  hundred 
years  or  more.  Probably  seventy-five  years  would  usually  be  a  safe 
figure.  Carefully  protected  riveted  pipe  will  also  have  a  very  long  life, 


218 


WATER-WORKS   CONSTRUCTION  IN  GENERAL. 


TABLE  NO.   35. 

AMOUNTS    NECESSARY  TO   INVEST   AT  VARIOUS   RATES   OF   COMPOUND   INTEREST   TO' 

ACCUMULATE    $I.OO   AT   THE    END   OF    VARIOUS    PERIODS    OF    TIME.      THE 

PAYMENT   IS    ASSUMED    TO    BE    MADE   AT    THE    END   OF    EACH    YEAR. 


Year. 

Rates  of  Interest  in  Per  cent. 

2  Per  cent. 

2\  Per  cent. 

3  Per  cent. 

Z\  Per  cent. 

4  Per  cent. 

I 

$1  .  OOOOO 

$1  .  OOOOO 

$1  .  OOOOO 

$1  .  OOOOO 

$1  .  OOOOO 

2 

0.49505 

0.49382 

0.49261 

0.49140 

0.49020 

3 

0-32675 

0.32514 

0.32353 

0.32193 

0-32035 

4 

o.  24262 

0.24082 

0.23902 

0.23725 

0.23550 

5 

o.  19218 

o.  19025 

0.18835 

0.18648 

0.18463 

6 

0.15853 

0.15655 

O.I545I 

o.  15267 

0.15077 

7 

0.13451 

o.  13250 

0.13051 

o.  12854 

o.  12661 

8 

o.  11651 

o.  11458 

o.  11246 

o.  11048 

0.10853 

9 

o.  10252 

o.  10046 

0.09843 

0.09644 

0.09449 

10 

0.09133 

0.08926 

0.08723 

0.08524 

0.08329 

ii 

0.08218 

0.08011 

0.07808 

0.07609 

0.07411 

12 

0.07456 

0.07250 

0.07047 

0.06848 

0.06655 

13 

0.06812 

o  .  06605 

0.06403 

0.06205 

0.06015 

14 

0.06260 

0.06054 

0.05853 

0.05657 

0.05467 

15 

0.05782 

0-05577 

0.05380 

0.05183 

0.04994 

16 

0.05365 

0.05160 

0.04961 

0.04768 

0.04582 

17 

0.04997 

0.04793 

0.04595 

o  .  04404 

0.04220 

18 

0.04670 

0.04470 

0.04271 

o  .  04082 

0.03899 

19 

0.04378 

0.04176 

0.03981 

0.03794 

0.03614 

20 

0.04116 

0.03915 

0.03722 

0.03536 

0.03356 

21 

0.03878 

0.03678 

0.03487 

0.03304 

0.03128 

22 

0.03663 

0.03465 

0.03270 

0.03094 

0.02920 

23 

0.03467 

0.03270 

0.03081 

0.02902 

0.02731 

24 

0.03287 

0.03091 

0.02905 

0.02727 

0.02560 

25 

0.03122 

0.02928 

0.02743 

0.02567 

0.02401 

26 

0.02970 

0.02777 

0.02594 

0.02421 

0.02257 

27 

0.02821 

0.02640 

0.02460 

0.02285 

0.02124 

28 

0.02699 

0.02509 

0.02329 

o.  02161 

0  .  02000 

29 

0.02578 

0.02389 

O.O22II 

0.02045 

0.01888 

3° 

0.02465 

0.02278 

O.O2IO2 

0.01937 

0.01783 

0.02360 

0.02174 

O.O2000 

0.01837 

0.01686 

32 

0.02261 

0.02077 

O.OI9O5 

0.01744 

0.01595 

33 

0.02169 

0.01986 

o.  01816 

0.01657 

O.OI5II 

34 

0.02082 

0.01901 

0.01732    . 

0.01576 

O.OI43I 

35 

O.O2OOO 

0.01821 

0.01654 

0.01499 

0.01358 

36 

0.01923 

0.01745 

0.01580 

o.  01426 

0.01288 

37 

0.01851 

0.01674 

6.0I5II 

0.01361 

0.01224 

38 

0.01781 

0.01607 

0.01450 

0.01298 

0.01163 

39 

O.OI7I7 

0.01544 

0-01383 

0.01240 

o.  01106 

40 

0.01655 

0.01484 

0.01326 

0.01183 

0.01052 

41 

o.o!597 

0.01427 

O.OI27I 

0.01130 

O.OIOO2 

42 

0.01542 

0.01373 

O.OI2I9 

0.01080 

0.00954 

43 

0.01489 

0.01322 

O.OII70 

0.01033 

o  .  00909 

44 

0.01439 

0.01273 

O.OII23 

0.00987 

0.00866 

45 

0.01391 

0.01226 

O.OI08O 

0.00945 

0.00826 

46 

0.01345 

0.01183 

0.01036 

0.00905 

0.00788 

47 

0.01302 

0.01141 

0.00996 

o  .  00866 

0.00752 

48 

0.01260 

0.01097 

0.00957 

0.00830 

0.007l8 

49 

O.  01220 

0.01066 

O.O09l8 

0.00796 

0.00686 

50 

O.OII82 

0.01026 

0.00886 

0.00763 

0.00655 

DEPRECIATION  OF  STRUCTURES. 
TABLE  NO.   35. —  Continued. 


219 


Year. 

Rates  of  Interest  in  Per  cent. 

2  Per  cent. 

2\  Per  cent. 

3  Per  cent. 

3^  Per  cent. 

4  Per  cent. 

51 

$0.01146 

$0.00991 

$0.00853 

$0.00732 

$0.00626 

52 

O.OIIII 

0.00957 

0.00822 

0.00703 

0.00598 

53 

0.01077 

0.00925 

0.00791 

0.00674 

0.00572 

54 

0.01045 

o  .  00894 

0.00763 

0.00647 

0.00547 

55 

0.01014 

0.00866 

0.00735 

0.00622 

0.00523 

56 

o  .  00984 

0.00837 

0.00709 

0.00597 

0.00501 

57 

0.00956 

0.00810 

0.00683 

0.00573 

0.00479 

58 

0.00929 

0.00784 

0.00659 

0.00550 

0.00458 

59 

o  .  00902 

0.00759 

0.00635 

0.00529 

0.00439 

60 

0.00877 

0.00735 

0.00613 

0.00507 

0.00420 

61 

0.00852 

0.00712 

0.00592 

o  .  00489 

o  .  00402 

62 

0.00828 

0.00690 

0.00571 

0.00471 

0.00385 

63 

o  .  00806 

0.00669 

0.00552 

0.00453 

0.00369 

64 

0.00784 

o  .  00648 

0.00533 

0.00435 

0-00353 

65 

0.00763 

0.00628 

0.00515 

0.00418 

0.00339 

66 

0.00742 

o  .  00609 

0.00497 

0.00403 

0.00325 

67 

0.00722 

0.00591 

o  .  00480 

0.00388 

0.00311 

68 

0.00704 

0.00573 

0.00465 

0.00373 

0.00298 

69 

0.00685 

0.00556 

o  .  00449 

0.00359 

O.O0286 

70 

0.00667 

0.00540 

0.00434 

0.00346 

O.OO274 

7i 

o  .  00649 

0.00524 

0.00419 

0.00333 

0.00263 

72 

0.00633 

o  .  00508 

o  .  00405 

0.00321 

0.00252 

73 

0.00616 

0.00493 

0.00392 

0.00309 

O.00242 

74 

0.00601 

0.00479 

0.00379 

0.00298 

O.OO232 

75 

0.00585 

o  .  00465 

0.00367 

0.00287 

O.OO223 

76 

0.00571 

0.00452 

0.00355 

0.00277 

O.OO2I4 

77 

0.00557 

0.00439 

0.00343 

0.00266 

O.002O5 

78 

0.00542 

0.00426 

0.00333 

0.00257 

O.OOI97 

79 

0.00529 

0.00414 

0.00321 

0.00247 

0.00189 

80 

0.00516 

o  .  00403 

0.00311 

0.00239 

O.OOlSl 

81 

0.00503 

0.00391 

0.00301 

0.00230 

O.OOI74 

82 

0.00491 

o  .  00380 

0.00292 

O.OO222 

0.00167 

83 

9.  00479 

0.00369 

0.00282 

O.OO2I4 

O.OOl6o 

84 

0.00468 

0.00359 

0.00273 

O.OO2O6 

O.OOI54 

85 

0.00456 

0.00349 

0.00264 

0.00199 

0.00148 

86 

0.00445 

o  .  00340 

0.00256 

O.OOI92 

O.OOI42 

87 

0.00434 

0.00330 

0.00248 

O.OOl85 

0.00136 

88 

0.00424 

0.00321 

0.00240 

0.00178 

O.OOI3I 

89 

0.00414 

0.00312 

0.00233 

O.OOI72 

0.00126 

90 

o  .  00405 

0.00304 

0.00225 

O.OOl66 

O.OOI2I 

9i 

0.00395 

0.00295 

0.00219 

0.00l6o 

o.  00116 

92 

o.  00386 

0.00287 

O.OO2I2 

O.OOI54 

O.OOIII 

93 

0.00377 

0.00280 

o  .  00205 

O.OOI49 

O.OOIO7 

94 

0.00368 

0.00271 

O.OOI99 

O.OOI44 

O.OOIO3 

95 

0.00360 

0.00265 

0.00193 

0.00138 

o  .  00099 

96 

0.00351 

0.00258 

0.00187 

0.00134 

O.OOO95 

97 

0.00343 

0.00251 

O.OOlSl 

O.OOI29 

O.OOO9I 

98 

0.00336 

o.  00244 

0.00175 

0.00125 

o  .  00087 

99 

0.00328 

0.00237 

0.00170 

O.OOI2I 

0.00084 

100 

0.00320 

0.00231 

0.00165 

o.  00116 

O.OOoSl 

220  WATER-WORKS   CONSTRUCTION  IN  GENERAL. 

but  not  so  long  as  cast  iron.  Large,  well-made  machinery  may  have  a  life 
of  thirty  or  forty  years,  or  perhaps  longer,  but  improvements  in  the 
design  of  machinery  would  usually  limit  its  useful  life  to  twenty-five  or 
thirty  years.  The  life  of  boilers  will  usually  range  from  fifteen  to 
twenty  years.  Light  machinery  will  have  a  life  of  fifteen  or  twenty 
years,  and  in  some  cases  of  great  wear  even  less  than  this. 

In  many  problems,  especially  in  the  appraisal  of  water-works  proper- 
ties, the  determination  of  the  present  value  of  a  depreciated  plant  is  nec- 
essary. Considering  the  plant  as  one  to  be  indefinitely  maintained  on  a 
steady  financial  basis,  the  present  worth  of  a  depreciated  plant  must  be 
such  a  value  as  will,  when  added  to  the  present  value  of  the  annuity  set 
aside  for  its  depreciation,  just  equal  its  first  cost ;  that  is,  neglecting' fluc- 
tuations in  cost,  the  present  value  of  the  plant  and  that  of  the  annuity 
set  aside  for  its  replacement  should  at  all  times  be  a  constant  quantity. 
This  is  what  is  usually  called  the  "  sinking  fund  basis."  The  present 
worth  can  readily  be  obtained  from  Table  35.  Thus,  suppose  the  life 
of  a  structure  be  forty  years,  and  the  rate  of  interest  three  per  cent. 
Required,  the  value  of  the  plant  twenty-five  years  after  its  construction. 
From  the  table,  the  annuity  required  to  cover  depreciation  is  $0.01326 
per  dollar  for  forty  years.  The  annuity  required  to  produce  $1.00  at 
the  end  of  twenty-five  years  is  $0.02743.  The  value  of  the  annuity  of 
$0.01326  at  the  end  of  twenty-five  years  is  therefore  equal  to  .01 326  •*- 
.02743  =  $.483.  This  amount  may  be  considered  the  amount  of  depre- 
ciation per  dollar  at  the  end  of  twenty-five  years,  and  the  present  worth 
is  therefore  equal  to  $1.00  —  .483  =  $.5 17  per  dollar,  or  51.7  per  cent  of 
the  first  cost.  For  further  discussion  see  Chapter  XXIX. 

244.  Provision  for  the  Future.  —  In  the  preceding  discussion  the 
matter  of  permanence  only  has  been  mentioned.  Another  very  im- 
portant element  needs  to  be  considered  at  all  points  of  the  design, 
namely,  what  provision  is  it  economical  and  expedient  to  make  for  the 
future  ?  The  questions  of  future  population  and  consumption  have 
already  been  discussed,  and  it  is  here  assumed  that  these  have  been 
settled.  There  remains  then  to  be  determined  the  capacity  of  the 
various  parts  of  the  work.  Obviously,  those  portions  of  the  works  that 
can  be  added  to  as  easily  at  one  time  as  another,  such  as  pumps, 
filters,  etc.,  should  be  built  for  but  little  more  than  present  require- 
ments. Future  requirements,  however,  should  be  regarded  rather  more 
than  strict  economy  would  suggest  owing  to  delays  and  difficulties 
in  securing  appropriations,  etc.  Other  parts,  such  as  pump-houses, 
land  for  filter-beds,  pumping-mains,  etc.,  should  be  designed  for  a 
longer  time  in  the  future,  as  these  are  obtained  more  cheaply  per  unit 


ESTIMATES   OF  COST.  221 

of  capacity  at  first  than  by  duplication.  Still  other  parts,  such  as 
masonry  conduits,  dams,  tunnels,  etc.,  should  be  built  for  a  still 
greater  capacity,  as  the  extra  cost  and  depreciation  will  both  be 
relatively  small. 

The  question  to  be  answered  is,  how  much  will  it  pay  to  spend  now 
in  securing  capacity  in  the  various  parts  of  the  works  in  order  to  avoid 
the  expenditure  of  a  larger  sum  in  the  future  ?  It  is  a  simple  problem 
in  compound  interest,  and  is  solved  by  determining  what  sum  of  money 
placed  at  compound  interest  will  amount  to  the  sum  saved  at  the  time 
the  increased  capacity  becomes  necessary.  If  A  —  amount  saved  at 
the  end  of  n  years  by  incurring  a  certain  expense  B  at  the  present  time, 
and  r  —  rate  of  interest,  then  in  order  that  the  one  plan  may  just 
balance  the  other  we  have  A  =  B(i  -\-  r)nt  or 


If  the  structure  under  consideration  is  subject  to  depreciation,  the 
amount  A  must  be  figured  on  the  basis  of  the  actual  value  of  the 
depreciated  plant  at  the  given  time  in  the  future. 

To  arrive  at  a  proper  solution  it  is  necessary  to  take  into  considera- 
tion many  other  elements  than  merely  the  mathematical  one  of  interest. 
All  parts  of  a  works  should  be  made  to  correspond,  or  be  so  designed 
that  future  enlargements  of  one  part  will  correspond  to  the  more 
permanent  structures  of  another  part.  Thus  a  metal  portion  of  a  con- 
duit may  well  be  made  just  one-half  or  one-third  the  capacity  of  the 
masonry  portion  of  the  same,  the  former  providing  for  ten  or  fifteen 
years  in  the  future,  while  the  latter  provides  for  thirty  or  forty  years. 
There  must  also  be  considered  the  question  of  the  financial  ability  of 
the  community  to  incur  a  large  expense  or  a  large  annual  payment, 
the  debt  limit,  etc.  These  factors  will  often  necessitate  the  construc- 
tion of  a  plant  which  might  not  be  the  ideal  one  with  unlimited  capital 
at  hand. 

245.  Estimates  of  Cost.  —  To  be  of  much  value  an  estimate  of  cost 
must  be  made  from  classified  estimates  of  the  different  kinds  of  work 
to  be  done  and  material  to  be  furnished.  In  work  of  the  nature  of  most 
of  that  involved  in  water-works  construction  the  risk  is  not  great,  and 
close  estimates  can  be  made  of  the  cost  of  various  classes  of  work  by 
inquiry  of  local  contractors  and  by  comparison  with  the  cost  of  similar 
work  already  executed.  The  contract  prices  quoted  in  the  technical 
papers  will  be  of  assistance  in  this  connection.  The  analysis  of  the  cost  of 


222  WATER-WORKS   CONSTRUCTION  IN    GENERAL. 

various  classes  of  masonry  given  in  Baker's  "  Masonry  Construction  " 
will  also  be  found  useful.  Prices  of  metal  parts,  such  as  pipes,  valves, 
machinery,  etc.,  vary  so  greatly  from  time  to  time  that  any  statement 
of  them  would  be  of  little  permanent  value.  Approximate  prices  can 
always  be  obtained  on  short  notice  by  correspondence  with  manufac- 
turers. 

Although  the  classified  estimate  is  the  only  reliable  way  of  estimat- 
/ng  the  cost  of  a  works,  yet  it  is  very  useful  to  an  engineer,  when  consid- 
ering the  possibilities  of  different  schemes,  to  have  in  mind  certain 
rough  general  figures  of  cost  of  the  different  parts  of  a  system .  Such,  for 
example,  as  the  cost  of  small  pipe  systems  per  mile,  cost  of  reservoirs 
of  different  kinds  per  1000  or  1,000,000  gallons  capacity,  cost  of  filters 
per  million  gallons  capacity,  etc.  In  what  follows  such  general  figures 
of  the  cost  of  works  have  in  many  cases  been  given,  but  it  must  be 
remembered  that  they  can  be  used  only  in  making  rough  preliminary 
estimates. 

LITERATURE. 

1.  Francis.     Some   Notes   on    Different   Systems   of  Water-supply.     Eng. 

News,  1886,  xv.  p.  165. 

2.  Ellis.     Fire  Protection  by  Direct  High  Pressure  from  Pumps  in  Combined 

Pumping  and  Reservoir,   or  Stand-pipe  Systems.     Jour.  New  Eng. 
W.  W.  Assn.,  1892,  vii.  p.  27. 

3.  McElroy.     City  Water-supplies  of  the  Future.     Eng.  Mag.,    1894,  vi. 

p.  821. 

4.  Brackett.     Water-supply  of  Different  Qualities   for  Different  Purposes. 

Report  Mass.  Board  of  Health  on  Metropolitan  Water-supply,  1895, 
p.  217. 

5.  Sources,  Modes  of  Supply  and  Filtration  of  Public  Water-supplies  in  the 

United  States.     Eng.  News,  1898,  XL.  p.  9. 

6.  Crowell.    Report  of  a  Proposed  Sea-water  Fire  Pipe-line  for  the  City  of 

New  York,  1897.     Eng.  Record,  1898,  xxxvu.  p.  124. 

7.  Weston.     The  Separate  High-pressure  Fire-service  System  of  Providence, 

R.  I.     Jour.  New  Eng.  W.  W.  Assn.,  1898,  xm.  p.  85. 

8.  Miller.     Report   on    a    Proposed    Salt-water    Street-sprinkling   Plant   at 

Oakland,  Cal.     Eng.  News,  XLII.  p.  149- 

9.  Hill.     The  Appraisal  of  Plants  for  Public  Services.     Eng.  Record,  1901, 

XLIII.  p.  546. 

10.  Alvord.     The    Financial   Questions   in    Water-works  Valuations.     Proc. 

Am.  W.  W.  Ass'n,  1903,  p.  473  ;  Eng.  Record,  1902,  XLVI.  p.  30. 

11.  Adams.     The  Principles  Governing   the  Valuation  for  Rate-fixing  Pur- 

poses of  Water-works  Under  Private  Ownership.     Jour.  Ass'n.  Eng. 
Soc.  1906,  xxxvi.  p.  37.     Eng.  Record,  1905,  LII.  p.  153. 


CHAPTER   XII. 
HYDRAULICS. 

246.  Purpose  of  the  Chapter. — In  the  present  chapter  it  is  proposed 
to  give  in  as  brief  a  form  as  possible  such  hydraulic  formulas  as  are  of 
frequent  use  in  the  design  of  water-works,  together  with  diagrams  and 
tables  of  coefficients  based  upon  the  latest  and  most  reliable  experi- 
ments. 

247.  Units  of  Measure. — The  unit  of  length  most  frequently  used  in 
hydraulics  is  the  foot.      The  unit  of  volume'  is  the  cubic  foot  or  the 
United  States  gallon.      The  unit  of  time  usually  employed  in  hydraulic 
formulas  is  the  second,  but  in  many  water-supply  problems  the  minute, 
the  hour,  and  the  day  are  also  often  used.      The  unit  of  weight  is  the 
pound,  and  that  of  energy  the  foot-pound. 

i  U.  S.  gallon  =  231  cubic  inches  =  0.1337  cubic  foot; 
i  cubic  foot  =  7.481  U.  S.  gallons; 
1.2  U.  S.  gallons  =  i  imperial  gallon. 

248.  Notation. — The  following  general  notation  will  be  used  in  the 
present  chapter  without  further  explanation : 

w  =  weight  of  a  cubic  foot  of  water  assumed  equal  to  62.5  pounds; 
g  =  acceleration  of  gravity  =32.2  feet  per  second  per  second; 
h  —  head  of  water ; 
/  =  pressure  of  water ; 
r  =  hydraulic  mean  radius ; 

s  =  sine  of  slope  of  hydraulic  grade-line  or  of  free  water-surface. 
Q  =  rate  of  discharge  or  flow ; 
v  =  velocity. 

249.  Weight  of  Water. — The  weight  of  distilled  water  at  different 
temperatures  is  given  in  Table  No.  36. 

The  weight  of  ordinary  water  is  greater  than  that  of  distilled  water 
on  account  of  the  impurities  contained.  For  ordinary  purposes  a 
cubic  foot  of  fresh  water  may  be  taken  equal  to  62.5  pounds.  Sea- 
water  will  weigh  about  64  pounds  per  cubic  foot. 

223 


224 


HYDKA  ULICS. 
TABLE   NO.  36. 

WEIGHT    OF    DISTILLED    WATER. 


Temperature, 
Fahrenheit. 

Weight,Pounds 
per  Cubic  Foot. 

Temperature, 
Fahrenheit. 

Weight,  Pounds 
3er  Cubic  Foot. 

32° 

62.42 

140° 

61.39 

39-3 

62.424 

160 

61.01 

60 

62.37 

1  80 

60.59 

80 

62.  22 

200 

60.  14 

100 

62.OO 

212 

59-84 

120 

61.72 

250.  Pressure  of  the  Atmosphere. — In  problems  pertaining  to  the 
operation  of  suction-pipes  it  is  important  to  know  the  atmospheric 
pressure  corresponding  to  various  elevations  above  sea-level.  Data 
pertaining  to  this  point  are  given  in  Table  No.  37  in  terms  both  of 
mercury  barometer  and  of  water  barometer.  The  figures  given  are 
average  values. 

TABLE   NO.  37. 

ATMOSPHERIC   PRESSURE   AT    DIFFERENT   ELEVATIONS. 


Elevation 
above  Sea-level 
Feet. 

Pressure  in 
Pounds  per 
Square  Inch. 

Height  of 
Mercury 
Barometer. 
Inches. 

Height  of 
Water 
Barometer. 
Feet. 

o 

14.7 

30.00 

340 

500 

14-5 

29.47 

33-3 

1,000 

14.2 

28.94 

32.8 

2,000 

13-7 

27.92 

31.6 

4,000 

12.7 

25.98 

29.4 

6,000 

ir.  8 

24.18 

27-4 

8,000 

II.  O 

22  50 

25.5 

10,000 

10.3 

20.93 

23.7 

251.  Vapor  Tension  of  Water. — Where  the  temperature  of  the  water 
is   high   the   elevation   of  the   water    barometer  will   be   considerably 
reduced  below  that  given   in   the  previous  table   on  account  of  the 
pressure  of  the  water  vapor.      Table  No.  38  gives  values  of  this  vapor 
tension  or  pressure  in  feet  of  head  for  various  temperatures. 

252.  Pressure  of  Water. — (i)  Pressure  at  a  Point.  —  The  pressure 
of  water  per  unit  of  area  at  a  distance  h  below  the  free  surface  is 


=  wh. 


PRESSURE   OF   WATER. 
TABLE   NO.  38. 

VAPOR   TENSION   OF   WATER. 


22$ 


Temperature, 
Fahrenheit. 

Pressure  in 
Pounds  per 
Square  Inch. 

Pressure  in 
Feet  of  Water. 

32° 

.09 

.21 

40 

.12 

.28 

60 

.26 

.60 

80 

.50 

1.  15 

IOO 

•95 

2.19 

1  20 

1.69 

3-91 

140 

2.89 

6.68 

160 

4-74 

II.  0 

180 

-    7-53  - 

17.4 

200 

11.56 

26.7 

212 

14.70 

34-o 

If  h  is  expressed  in  feet,  and  /  in  pounds  per  square  inch,  we  have 


and 


/  =  0.434^, (2) 

h  =  2.304/. (3) 


Pressures  are  very  commonly  stated  in  terms  of  the  head  ^,  in  which 
case  h  is  called  the  pressure-head. 

(2)  Pressure  on  a  Surface. — The  pressure  of  water  on  a  plane  sur- 
face is  always  normal  to  that  surface.     The  amount  of  the  pressure  is 


P  = 


(4) 


where  A  =  total  area  of  surface,  and  h  =  head  of  water  at  its  centre 
of  gravity.  The  component  of  the  pressure  in  any  given  direction  is 
equal  to  the  normal  pressure  upon  that  projection  of  the  given  surface 
at  right  angles  to  the  given  direction. 

(3)  Centre  of  Pressure. — The  centre  of  pressure  upon  a  submerged 
plane  surface  is  given  by  the  formula 


7 
=  5' 


(5) 


where  y  =  distance  of  centre  of  pressure  from  the  intersection  of  the 
plane  with  the  water-surface ;  and  7  and  5  are  respectively  the  moment 
of  inertia  and  the  statical  moment  of  the  area  about  this  intersection. 


226  HYDRA  ULICS. 

(4)  Bursting-pressure  in  Pipes.  —  The  bursting-pressure  per  lineal 
unit  in  a  pipe  of  diameter  d,  due  to  a  water-pressure  /,  is 

P,  =  fd.    .....     .     .     .     .     (6) 

If  /  =  thickness  of  pipe,  the  resulting  tensile  stress  per  unit  area  is 


<» 


In  a  closed  cylinder  under  pressure  the  force  tending  to  rupture  it 
transversely  is 

?,*^jp      •     •     • (») 

and  the  stress  per  unit  area  is 

-^-£  (9) 


or  one-half  that  given  by  equation   (7).      This  is  also  the  stress  in  a 
sphere  of  diameter  d. 

Formulas.  (6)  to  (9)  assume  that  the  water  in  the  pipe  or  cylinder 
is  under  a  uniform  pressure,  or,  in  other  words,  that  the  diameter  of 
the  pipe  is  small  as  compared  with  the  pressure  head  of  the  water. 

FLOW   OF   WATER   THROUGH    ORIFICES. 

253.  Form  and  Proportion  of  Orifices. — In  making  use  of  an  orifice 
for  measuring  water  it  is  desirable  that  it  be  made  in  such  a  way  as  to 
be  in  effect  an  orifice  in  a  thin   plate ;  that  is  to  say,  it  should  be  so 
arranged  that  the  water  in  passing  out  will  touch  the  .inner  edge  only. 
Furthermore,  it  is  important  that  the  inner  edge  of  the  orifice  shall  be 
flush  with  the  inner  surface  of  the    tank,  and  that  the  latter  should 
extend  as  a  plane  surface  for  a  considerable  distance  in  each  direction 
from  the  orifice.     To  secure  complete  contraction  the  orifice  should  be 
placed  at  a  distance  from  the  sides  and  the  bottom  of  the  tank  not  less 
than  three  times  the  width  of  the  orifice ;  and  in  order  that  the  effect 
of  the  velocity  of  approach  may  be  inappreciable  the  area  of  the  orifice 
should  not  exceed  one-twentieth  of  the  cross-section  of  the  tank. 

254.  Flow  through  Small  Orifices. — The  theoretical  velocity  of  water 
flowing  through  an  orifice  is,  at  the  point  of  contraction,  v  =  \/2gh, 
where  //  =  head  of  water  at  centre  of  orifice.      The  actual  velocity  is  a 
little  less  than  the  theoretical,  and  we  have 

V  =   C  V2gk, (10) 


FLO W  OF   WATER    THROUGH  ORIFICES. 


227 


in  which  c  is  a  coefficient,  found  by  experiment  to  be  equal  to  .97  to 
.98.  The  ratio  of  the  area  of  the  cross-section  of  the  contracted  vein 
to  the  area  of  the  orifice  is  called  the  coefficient  of  contraction.  It 
ranges  from  .6  to  .7,  but  usually  has  a  value  of  from  .62  to  .64. 
Finally,  if  A  =  area,  of  orifice,  the  discharge  is 


(II) 

in  which  cd  =  coefficient  of  discharge  =  about  .62.  Many  experiments 
have  been  made  to  determine  the  value  of  cd  directly. 

255.  Large  Rectangular  Vertical  Orifices. — The  discharge  is  given 
by  the  formula 

in  which  c  is  again  a  coefficient,  b  —  width,  hz  =  head  on  lower  edge 
of  orifice,  and  h^  =  head  on  upper  edge.  If  the  head  h  at  the  centre 
of  the  orifice  is  greater  than  four  times  the  height  of  the  orifice,  then 
it  is  sufficiently  exact  to  write 

in  which  d  =  vertical  dimension  of  the  orifice.  For  square  orifices 
b  =  d,  and  if  h  is  greater  than  4^,  then 


........      (14) 

Table  No.  39  contains  values  of  coefficients  for  square  orifices  as 
deduced  by  Hamilton  Smith  from  the  results  of  many  experiments. 

TABLE  NO.  39. 

COEFFICIENTS    FOR    SQUARE   VERTICAL   ORIFICES  .(SMITH). 


Head, 


Side  of  the  Square  in  Feet. 


in  Feet. 

O.O2 

0.04 

0.07 

O.I 

O.2 

0.6 

I.O 

OA 

o  64.*? 

0.628 

O.62I 

'  *f 

0.6 

0.660 

W.  V4+  J 

.636 

.623 

.617 

0.605 

0.598 

0.8 

.652 

.631 

.620 

.615 

.605 

.600 

0.597 

I.O 

.648 

.628 

.618 

.613 

.605 

.601 

•599 

i-5 

.641 

.622 

.614 

.610 

.605 

.6O2 

.601 

2.0 

.637 

.619 

.612 

.608 

.605 

.604 

.602 

2-5 

.634 

.617 

.610 

.607 

.605 

.604 

.602 

3 

.632 

.616 

.609 

.607 

.605 

.604 

.603 

4 

.628 

.614 

.608 

.606 

.605 

.603 

.602 

6 

.623 

.612 

.607 

.605 

.604 

.603 

.602 

8 

.619 

.610 

.606 

.605 

.604 

.603 

.602 

10 

.616 

.608 

.605 

.604 

.603 

.602 

.601 

20 

.606 

.604 

.602 

.602 

.6O2 

.601 

.600 

50 

.602 

.601 

.601 

.600 

.600 

•599 

•599 

100 

•599 

.598 

.598 

•598 

.598 

•598 

•598 

228 


HYDRAULICS. 


256.  Circular  Vertical  Orifices.  —  The  Discharge  from  large  circular 
vertical  orifices  is  given  by  the  formula 


where  d  =  diameter  of  orifice,  and  h  =  head  of  water  at  its  centre. 
If  h  is  greater  than  $d,  then  we  may  write 


Q  =  c.\nd*\/2gh (16) 

Table  No.  40  gives  values  of  c  as  deduced  by  Hamilton  Smith. 

TABLE   NO.  40. 

COEFFICIENTS    FOR    CIRCULAR    VERTICAL    ORIFICES    (SMITH). 


Diameter  of  Orifice  in  Feet. 

Head,  h, 

in  Feet. 

0.02 

0.04 

0.07 

O.IO 

0.2 

0.6 

I.O 

O  4 

060*7 

o  .  624 

o.  618 

w»«i 
0.6 

0.655 

•  u  o  i 
.630 

.618 

'.613 

0.601 

0.593 

0.8 

.648 

.626 

.615 

.610 

.601 

•594 

0.590 

I.O 

.644 

.623 

.612 

.608 

.600 

•  595 

•59* 

i-5 

•637 

.618 

.608 

.605 

.600 

•596 

•593 

2.0 

.632 

.614 

.607 

.604 

•599 

•597 

•595 

2-5 

.629 

.612 

.605 

.603 

•599 

•598 

•596 

3 

.627 

.611 

.604 

.603 

•599 

.598 

•597 

4 

.623 

.609 

.603 

.602 

•599 

•597 

•596 

6 

.618 

.607 

.602 

.600 

.598 

•597 

•596 

8 

.614 

.605 

,601 

.600 

.598 

.596 

.596 

10 

.611 

.603 

•599 

.598 

-597 

.596 

•595 

20 

.601 

•599 

•597 

•596 

•596 

.596 

•594 

50 

.596 

•595 

•594 

•594 

•594 

•594 

•593 

100 

•593 

•592 

•  592 

.592 

•592 

•592 

•592 

FLOW   OF   WATER    OVER   WEIRS. 

257.  Sharp-crested  Weirs.  —  For  measuring  the  flow  of  a  small 
stream  a  weir  is  very  often  employed.  Such  weirs  are  usually  rectan- 
gular and  are  made  sharp-crested,  that  is,  of  a  form  such  that  the  water 
touches  the  inside  edge  only.  The  back  of  the  weir  should  be  a 
vertical  plane  surface.  If  the  ends  of  the  weir  are  placed  at  some  dis- 
tance from  the  sides  of  the  channel,  the  stream  of  water  will  be 
contracted  laterally.  For  complete  contractions  this  distance  should 
be  at  least  three  times  the  height  of  the  weir.  If  the  ends  are  flush 
with  the  sides  of  the  channel,  there  will  be  no  end  contractions. 


FLOW   OF   WATER   OVER    WEIRS. 


229 


The  depth  of  the  water  on  a  weir  should  be  measured  sufficiently 
far  above  the  weir  to  eliminate  the  effect  of  the  surface  curve. 

The  formula  for  discharge  from  a  rectangular  weir  may  be  written 
from  equation  (12)  by  putting  hl  =  o.  It  is 


(17) 


where  /  =  length  of  weir  and  H  =  height  of  water  on  the  weir.  If  the 
channel-  is  small,  the  velocity  of  approach  will  have  an  appreciable 

v* 
effect  upon  the  discharge.      If  h  =  head  due  to  this  velocity  =  —  , 

then  this  factor  is  commonly  taken  account  of  by  the  use  of  the  equa- 
tion 

Q=(;VYTg(ff+nK?  .....     (18) 

in  which  n  is  a  coefficient  varying  from  i  to  1.5.  The  velocity  of 
approach  can  be  estimated  with  sufficient  accuracy  by  first  determining 
the  value  of  Q  with  the  term  nh  omitted,  then  using  this  value  of  Q  to 
determine  v,  and  then  a  more  accurate  value  of  Q,  etc.  From  a  care- 
ful analysis  of  the  experiments  of  Francis,  Fteley  and  Stearns,  and 
others,  Hamilton  Smith  has  adopted  values  for  n  of  1.4  for  weirs  with 
end  contractions,  and  i£  for  weirs  with  contractions  suppressed.  From 
his  study  of  the  experiments  referred  to  he  has  also  derived  the 
values  for  the  coefficient  c  as  given  in  Tables  Nos.  41  and  42. 

TABLE   NO.  41. 

COEFFICIENTS    FOR    CONTRACTED   WEIRS    (SMITH). 


Length  of  Weir  in  Feet. 


Effective 

Head  in 
Feet. 

0.66 

i 

2 

3 

5 

10 

19 

O.I 
0.15 
0.2 
O.25 

0-3 
0.4 

0-5 

0.6 

0.  1 

0.632 
.619 
.611 
.605 
•  6oi 
•595 
•590 
•587 

0.639 
.625 
.618 
.612 
.608 
.601 
.596 
•593 

CGO 

0.646 

.634 
.626 
.621 
.6l6 
.609 
.605 
.601 
CfvB 

0.652 
.638 
•630 
.624 
.619 
.613 
.608 
.605 
601 

0.653 
.640 
.631 
.626 
.621 
.615 
.611 
.608 
606 

0.655 
.641 

•633 
.628 
.624 
.6l8 
.615 
.613 
612 

0.656 
.642 
.634 
.629 
.625 
.620 
.617 
.615 
61/1 

o  8 

.  syo 

CQC 

.UUJ 

6ll 

•U14 
611 

O    Q 

•  DVD 

eQ« 

6oi 

600 

.  ui  j 
612 

I    O 

COO 

•  3y° 

CQC 

60  1 

.uuy 
608 

611 

I    2 

c«e 

•  Dya 

CQT 

cn7 

f)QC 

610 

1.4. 

580 

e«7 

C.QA 

602 

600 

1.6 

.c8a 

.  5QI 

.600 

607 

230 


HYDRAULICS. 


TABLE   NO.    42. 

COEFFICIENTS    FOR    SUPPRESSED    WEIRS   (SMITH). 


Effective 
Head  in 
Feet. 

Length  of  Weir  in  Feet. 

19 

10 

7 

5 

4 

3 

a 

O.I 

0.657 

0.658 

0.658 

0.659 

0.15 

.643 

.644 

•645 

.645 

0.647 

0.649 

0.652 

0.2 

.635 

.637 

.637 

.638 

.641 

.642 

.645 

O.25 

.630 

.632 

.633 

.634 

.636 

•  638 

.641 

0-3 

.626 

.628 

.629 

.631 

.633 

.636 

.639 

0.4 

.621 

.623 

.625 

.628 

.630 

.633 

•636 

0-5 

.619 

.621 

.624 

.627 

.630 

.633 

•637 

0.6 

.618 

.620 

.623 

.627 

.630 

.634 

.638 

0-7 

.618 

.620 

.624 

.628 

.631 

•635 

.640 

0.8 

.618 

.621 

.625 

.629 

.633 

.637 

.643 

0.9 

.619 

.622 

.627 

.631 

.635 

•639 

645 

I.O 

.619 

.624 

.628 

•633 

•637 

.641 

.648 

1.2 

.620 

.626 

.632 

•636 

.641 

.646 

1.4 

.622 

.629 

.634 

.640 

.644 

1.6 

.623 

.631 

•637 

.642 

.647 

Mr.  James  B.  Francis  from  his  elaborate  series  of  experiments  a> 
Lowell*  on  a  weir  10  feet  long,  and  operating  under  heads  of  0.4  to 
1.6  feet  derived  the  formula  for  weirs  without  end  contractions, 


Q  =  3. 


and  with  contractions 


(19) 

(20) 


If  there  be  but  one  contraction,  o.iH  is  to  be  used  instead  of  O.2//. 
To  take  account  of  the  velocity  of  approach,  the  formulas  become 


and 


(22) 


in  which  h  =  — .      In  these  formulas  the  unit  of  length  is  the  foot. 

The  most  elaborate  series  of  experiments  on  weirs  ever  made  is 
that  which  has  been  carried  out  by  Bazin,  and  which  is  reported  in  the 
Annals  des  Fonts  et  Chaussees  for  the  years  1888-98.  The  formula 
deduced  by  him  for  sharp-crested  weirs  with  no  end  contractions  is  in 
foot  units 


•     (33) 


*  Lowell  Hydraulic  Experiments.     New  York,  1871. 


FLOW  OF   WATER   OVER    WEIRS. 


231 


in  which  /  =  height  of  weir  above  the  bottom  of  the  channel,  and  h  is 
the  actually  observed  head  on  the  weir,  The  velocity  of  approach  is 
taken  account  of  in  the  formula.  This  formula  gives  slightly  larger 
values  for  the  discharge  than  the  Francis  formula.* 

258.  Submerged  Weirs.  — As  the  result  of  an  analysis  of  the  experi- 
ments of  Francis  and  of  Fteley  and  Stearns,  Mr.  Herschel  t  adopts  the 
following  formula  for  discharge,  for  submerged,  sharp-crested  weirs 
without  end  contractions : 

0==3.33/e*#)';      .     .     .     .    T  .     (24) 
where  /  =  length  of  weir ; 

H  —  height  on  the  weir  on  the  up-stream  side ; 
n  =  a  coefficient,   depending  on  the  ratio  of  the  head  on  the 

down-stream  side  H'  to  the  head  H. 
The  values  of  n  are  given  in  Table  No.  43. 

TABLE    NO.   43. 

VALUES    OF    n    FOR    SUBMERGED    WEIRS.      (HERSCHEL.) 


H1 

H> 

H' 

H' 

H 

n 

H 

n 

H 

n 

H 

* 

.OO 

I.OOO 

.20 

0.985 

•45 

0.912 

.70 

0.787 

.02 

I.  006 

•25 

0-973 

.50 

0.892 

•  75 

0.750 

•05 

1.007 

.30 

0-959 

•55 

0.871 

.80 

0.703 

.10 

1.005 

•  35 

0.944 

.60 

0.846 

.90 

0.574 

•15 

0.996 

.40 

0.929 

.65 

0.819 

1.  00 

0.000 

259.  Weirs  of  Various  Forms.  —  In  many  cases  it  is  desirable  to 
determine  the  flow  of  a  stream  by  measurements  taken  of  the  height  of 
water  flowing  over  some  dam  or  weir;  and,  on  the  other  hand,  in  the 
design  of  waste-weirs  some  method  of  estimating  their  capacity  is 
essential.  The  law  of  flow  over  such  weirs  is  very  complicated,  and 
the  only  accurate  way  of  determining  the  constants  for  any  particular 
case  is  by  means  of  experiments  on  a  section  of  the  same  form  as  the 
one  in  question.  If  this  is  impossible,  the  best  substitute  for  it  is  to  use 
constants  which  have  been  determined  for  a  weir  agreeing  as  closely 
in  form  as  may  be  to  the  one  under  consideration. 

Here  again  Bazin's  work  is  of  the  greatest  value.  He  employed 
in  his  experiments  weirs  of  a  great  variety  of  form.  The  heights  used 
were  one  metre  and  one  and  one-half  metres ;  and  the  heads  employed 
reached  a  maximum  of  about  one-half  metre.  The  end  contractions 

*  See  a  valuable   paper  by  G.   W.   Rafter,  including  exhaustive  discussion,  in 
Trans.  Am.  Soc.  C.  E.,  Dec.  1900. 

f  Trans.  Am.  Soc.  C.  E.,  1885,  xiv.  p.  194. 


232 


HYDRA  ULICS. 


were  suppressed  in  all  cases,  and  below  the  weir  the  sides  of  the 
channel  were  continued  so  that  in  general  there  was  not  perfectly  free 
access  of  air  beneath  the  sheet  of  water.  In  Table  No.  44  are  given 
values  of  the  coefficient  C  in  the  formula  Q  =  Clh*,  for  several  forms 
of  weirs,  as  deduced  from  Bazin's  experiments.  The  head  h  is  in  all 

TABLE   NO.   44. 

VALUES  OF  THE  COEFFICIENT  C"  IN   THE  FORMULA  Q=Clh*t  FROM  BAZIN'S  EXPERIMENTS. 


No. 


Section  of  Weir. 


Height  on  Weir  in  Feet. 


0.4  0.6  0.8  i.o  1.2  1.4 


10 


II 


II 


4.06 


3-40 


3-18 


3.26 


3-41 


3.20 


3-47 


3.20 


3-14 


2.68 


3-74 


3.86 


4.20 


3.70 


3-37 


3-70 


3-74 


3.68 


3-72 


3.38 


3-44 


2.90 


3-8i 


3-87 


4.20 


3.88 


3-54 


4.06 


4.00 


4.02 


3.87 


3-56 


3.67 


3.13 


4.18 


3.98 


3-68 


3-92 


4.20 


4.26 


4.01 


3-74 


3-83 


3-35 


3-93 


4.02 


4-15 


4-05 


3.80 


4.00 


4.18 


4.42 


4-13 


3.85 


3-83 


3.52 


3.98 


4.08 


4.12 


4.10 


-3.88 


3.80 


4.24 


4.20 


4-23 


3-95 


3-86 


3.64 


4.02 


4.15 


FLO W  OF   WATER  OVER    WEIRS. 
TABLE  NO.  &.— Continued. 


233 


No. 


16 


18 


20 


21 


22 


Section  of  Weir. 


25 


Height  of  Weir  in  Feet. 


0.4  0.6  0.8  x.o  1.2  1.4 


3-44 


3.18 


2.77 


3.08 


3-24 


3-04 


3.06 


2.83 


3-56 


3-12 


2.80 


2.86 


3-40 


3-64 


3-34 


2.83 


3-33 


3-40 


3.12 


3.00 


3-54 


3-23 


2.85 


2.88 


3.76 


3.80 


3-49 


2.92 


3-49 


3.60 


3-19 


3-14 


3-15 


3-57 


3-34 


2.90 


2-93 


4.08 


3-94 


3-65 


3-05 


3-54 


3-76 


3.26 


3.18 


3-27 


3.62 


3-47 


2.97 


2.96 


4-36 


4.04 


3-79 


3.16 


3.60 


3-86 


3.36 


3.20 


308 


3.66 


3-56 


3  05 


2.98 


4.56 


3-90 


3-29 


3-64 


3-97 


3-48 


3-23 


3-47 


3.70 


3-64 


3.14 


3-00 


4-56 


234 


HYDRA  ULICS. 


TABLE   NO.  45. 

VALUES  OF   THE    COEFFICIENT  C  IN    THE    FORMULA  Q  =  Cl$t    FROM   THE    CORNELL 
UNIVERSITY   EXPERIMENTS. 


10 


II 


12 


Section  of  Weir. 


JO' 


Height  on  Weir  in  Feet. 


t-5 


3-51 


3-51 


3.81 


2-93 


3.29 


3-51 


3-59 


3.81 


3-37 


3-37 


3-37 


3-76 


3-68 


3-6i 


2.85 


3.12 


2.85 


3-23 


3-52 


3.62 


3.61 


3-20 


25 


3.33 


3.33 


3.68 


3.71 


3.68 


2.89 


3.20 


2.45 


2.82 


3-34 


3-47 


3-54 


3-57 


3-50 


3-31 


3-31 


3-68 


3.81 


3.65 


3-03. 


3-31 


2.49 


2.9O 


3-42 


3-55 


3.52 


3-63 


3.60 


3-29 


3-29 


3-70 


3-90 


3-72 


3-16 


3-45 


2.51 


2.90 


3-45 


3.62 


3-57 


3.62 


3-23 


3-25 


3-75 


4.00 


3.80 


3.30 


3-63 


2.56 


2.92 


3-47 


3-68 


3-55 


3-67 


(.84 


4.5 


3-16 


3.20 


3-83 


4.06 


3-93 


3-50 


3.78 


2-59 


2-95 


3-52 


3-72 


3.69 


3-71 


3.14 


3.21 


3-71 


3-92 


2.67 


3.80 


FLOW  OF   WATER    THROUGH  PIPES.  235 

cases  the  actually  observed  head  on  the  weir.  The  coefficients  as 
given  were  obtained  from  curves  plotted  from  Bazin's  results.* 

More  recently  Mr.  G.  W.  Rafter  and  Prof.  G.  S.  Williams  have 
made  for  the  United  States  Board  of  Engineers  on  Deep  Waterways 
an  important  series  of  experiments  at  the  Cornell  University  Hydraulic 
Laboratory,  t  In  these  experiments  the  height  of  water  on  the  weir 
was  carried  to  a  value  of  about  5  feet,  the  weir  being  6.58  feet  long 
and  from  4.6  to  4.9  feet  above  the  bottom  of  the  channel.  Free 
access  for  the  air  beneath  the  sheet  of  water  was  provided.  In  Table 
No.  45  are  given  coefficients  for  several  of  the  forms  experimented  on, 
for  use  in  the  formula  Q  =  CUf,  where  h  is  again  the  actually  observed 
head  on  the  weir.  These  values  were  deduced  from  the  data  and  dis- 
charge curves  given  in  Prof.  Williams'  discussion  of  Mr.  Rafter's  paper 
above  referred  to. 

It  is  important  to  note  that,  on  account  of  the  difference  in  condi- 
tions with  respect  to  the  entrance  of  air  below  the  sheet  of  water  in  the 
two  series  of  experiments  above  described,  it  appears  that  in  those 
forms  having  a  steep  down-stream  face  the  coefficients  from  Bazin's 
experiments  are  much  the  higher.  For  slopes  greater  than  one-to-one 
the  differences  are  small.  Note  also  that  weirs  with  wide  crests  give 
lower  coefficients  than  those  with  narrow  crests;  also  that  low  weirs 
give  higher  coefficients  than  high  weirs. 

FLOW   OF   WATER   THROUGH   PIPES. 

260.  General  Relations  between  Velocity  and  Pressure. — Let  A  BCD, 
Fig.  32,  be  any  pipe  in  which  there  occurs  a  steady  flow  of  water  from 

R 


FIG.  32. 

a  reservoir.  Let  kv  7/2,  etc.,  be  the  pressures  in  this  pipe  at  points 
£>,  C,  D,  etc. ;  let  zv  £2,  z3,  etc.,  be  the  elevations  of  the  pipe  at  these 
points  above  any  given  plane,  and  HQ  the  elevation  of  the  surface  of 
the  water  in  the  reservoir  above  this  plane.  Let^,  ^2,  ^3,  etc.,  be  the 

*  See  Rafter's  paper  in  Transactions  Am.  Soc.  C.  E.,  Dec.  1900,  for  a  compilation 
of  Bazin's  coefficients.    Also  W.  S.  Paper  No.  200,  U.  S.  G.  S.,  1907. 
t  Trans.  Am.  Soc.  C.  E.,  Dec.  1900,  pp.  266,  316. 


236  HYDRA  UL1CS. 

velocities  at  the  several  points  ;  they  will  be  inversely  proportional  to 
the  respective  cross-sections  of  the  pipe.  The  total  energy,  potential 
and  kinetic,  of  any  given  volume  of  water,  referred  to  the  datum  plane 

and    expressed    in    terms    of  head   or    elevation    is,    h  -\-  z  -)  --  ,    or 

v* 
H  -\-  —  .      If  there  be  no  loss  of  energy  in  passing  from  point  to  point, 

then 

v* 
h-\-z-\  --  =  a  constant,     .....     (25) 

which  is  Bernoulli's  theorem. 

In  the  flow  of  water  through  pipes  some  loss  of  energy  takes  place, 
or  rather  is  dissipated  as  heat  because  of  the  internal  friction  in  the 
water,  so  that  the  value  of  the  expression  written  above,  instead  of 
remaining  constant,  becomes  continually  smaller  as  the  water  advances. 
If  ///  =  loss  of  head  due  to  friction  between  points  B  and  C,  we  may 
write 


In  the  figure  the  line  EF,  the  ordinates  to  which  measured  from 
the  pipe  represent  the  pressures  in  the  pipe,  is  called  the  hydraulic 
grade-line  of  the  pipe.  If  the  pipe  is  of  uniform  size,  then  vl  =  v2 
=  ^3,  etc.,  whence  k^  +  ^  =  h2  -f-  £2  +  ^f  >  tnat  ^s>  tne  difference  of 
elevation  of  the  hydraulic  grade-line  at  any  two  points  represents  the 
head  lost  in  friction  between  these  two  points.  As  the  elevation  of  the 
hydraulic  grade-line  is  independent  of  the  elevation  of  the  pipe,  it  is 
convenient  to  refer  directly  to  the  datum  plane  and  to  write  H^  =  H,2 
-f-  hf.  If  the  pipe  lies  above  the  hydraulic  grade-line  at  any  point,  the 
pressure  there  will  be  less  than  atmospheric  and  the  pipe  will  act  as  a 
siphon,  provided  its  elevation  above  the  hydraulic  grade-line  does  not 
exceed  the  height  of  the  water-barometer  as  given  on  page  214. 

The  usual  problem  to  be  considered  in  the  flow  of  water  through 
pipes  is  to  trace  out  the  various  losses  of  head  which  take  place  between 
the  water  at  the  reservoir  and  at  any  point  on  a  pipe-line,  or,  in  other 
words,  the  head  required  (H^  —  H^)  to  overcome  friction  between  A  and 
B  and  to  cause  a  velocity  of  flow  equal  to  vv  The  relation  is 


NATURE   OF  FLUID    FRICTION.  237 

Or  if  between  any  two  points  in  a  pipe,  it  is 

v  *        V* 
H,  -  H.  =  ^  -  -±-  +  kf. 

2g        2g 

261.  Nature  of  Fluid  Friction. — The  resistance  to  the  flow  of  water 
through  pipes  may  be  considered  as  made  up  of  two  parts:    (i)  that 
due  to  the  friction  of  water  on  the  inner  surface  of  the  pipe, — a  function 
of  the  viscosity  of  the  water;  and   (2)  a  loss  of  energy  resulting  from 
eddies  produced  in  the  water  by  irregularities  in  the  surface  of  the  pipe. 
Until  quite  recently  the  great  importance  of  the  second  factor  has  not 
been  appreciated.    Where  water  flows  through  a  pipe  with  a  rough  inner 
surface,  such  as  a  riveted  steel  pipe,  a  great  disturbance  is  caused  in 
the  stream  of  water,  which  may  extend  entirely  through  the  mass ;  and 
it  is  the  internal  work  of  friction  resulting  from  these  eddies,  and  the 
churning  up  of  the  water  caused  by  projecting  rivets  and  plates,  that 
constitutes  by  far  the  larger  portion  of  the  total  energy  consumed  in 
the  flow.     The  total  loss  of  head  in  a  pipe  such  as  here  mentioned  is 
thus  very  much  greater  than  that  which  occurs  in  a  smooth  pipe  whose 
diameter  is  equal  to  the  clear  diameter  of  the  rough  pipe.     With  very 
rough  channels  almost  the  entire  loss  of  head  is  chargeable  to  this 
element  of  internal  friction  due  to  eddies.      In  speaking,   therefore,  of 
the  fluid  friction  in  pipes  it  is  necessary  to  bear  in  mind  that  it  is  prin- 
cipally internal  friction,   and  to  a  very  slight  extent  a  friction  of  the 
water  upon  the  surface  of  the  channel. 

The  relative  importance  of  resistance  due  to  viscosity  and  that  due 
to  internal  friction  depends  much  upon  the  velocity  of  the  flow  and  the 
diameter  of  the  pipe,  as  well  as  upon  the  roughness  of  the  channel. 
For  low  velocities  and  small  diameters  the  resistance  is  largely  due  to 
viscosity,  in  which  case  it  varies  closely  with  the  velocity.  At  ordinary 
and  high  velocities  it  is  due  largely  to  internal  friction  and  varies  nearly 
as  the  square  of  the  velocity.  These  relations  are,  however,  much 
influenced  by  the  roughness  of  the  channel. 

262.  General  Formulas. — Owing  to  the  variation  in  the  general  law 
due  to  variation  in  conditions,  as  noted  in  the  foregoing  article,  it  is 
impossible  to  derive  a  formula  which  will  apply  to  all  cases.      The  best 
that  can  be  done  is  to  select  a  form  of  expression  which  will  approxi- 
mately represent  the  law,  and  then  to  make  use  of  coefficients  by  which 
the  results  of  experiments  may  be  conveniently  expressed  and  utilized. 
The  approximate  law  commonly  used  is  that  the  loss  of  head  varies 
with  the   square   of  the   velocity,    with   the   length   of  the   pipe,    and 
inversely  with  its  diameter.     Variations  due  to  differences  in  the  char- 


238  HYDRA  ULICS. 

acter  of  the  surface  of  the  pipe,  and  deviations  from  the  assumed  law 
due  to  other  causes,  are  taken  account  of  in  the  coefficient.  The  form 
of  expression  employed  in  theoretical  discussions  and  to  some  extent 
in  practical  problems  is 


in  which  //  =  loss  of  head  ; 
f  =  friction  factor  ; 
/  =  length  of  pipe  ; 
d  =  diameter. 

The  value  of  fin  this  expression  is  an  abstract  number,  and  there- 
fore the  same  for  any  system  of  units.  Tables  giving  values  of/"  for 
smooth  cast-iron  pipes  are  given  in  various  works  on  hydraulics  ;  these 
values  vary  from  about  .01  for  large  pipes  and  high  velocities  to  .03 
for  small  pipes  and  low  velocities. 

In  practice  the  use  of  a  coefficient  /is  somewhat  inconvenient.  A 
more  commonly  used  form  of  expression,  and  one  which  is  applied  also 
to  open  channels,  is  the  Chezy  formula: 

v  =  cVrs,  ........     (28) 

in  which  r  =  hydraulic  mean  radius; 

s  =  hydraulic  slope  =  -j\ 

c  =  a  coefficient. 

In  the  case  of  a  pipe  flowing  full,  r  =  \d. 

In  the  above  formula  the  value  of  c  will  be  different  for  different 
systems  of  units.  In  most  cases  the  foot  and  second  are  assumed  to 
be  used.  Note  that  the  coefficient  c  in  this  formula  is  equivalent  to 

'—-j="  of  formula  (27).     Various  expressions  and  values  for  c  have  been 

proposed  by  different  investigators  for  different  materials  and  under 
different  conditions. 

263.  Coefficients  and  Formulas  for  Cast-iron  Pipes.  —  The  greatest 
attention  has  been  given  to  the  flow  of  water  through  smooth  pipes  of  a 
character  similar  to  new,  or  nearly  new,  cast-iron  and  smooth  wrought- 
iron  pipes.  The  most  reliable  and  thorough  examination  of  experiments 
of  this  character  is  probably  that  by  Hamilton  Smith.*  The  results  of 
his  investigation  are  given  in  the  form  of  tables  and  diagrams  of  values 
of  c  in  the  Chezy  formula  for  various  velocities  and  diameters  of  pipes. 

*  Hydraulics.     N.  Y.,  1886. 


COEFFICIENTS  AND   FORMULAS  FOR   CAST-IRON  PIPES.        239 


VELOCITY,  IN  FEET  PER, SEC. 


6 


50 


40 


(6 

o 

5 

i 

10  rj 


00 


90 


80 


2  4  6  8  10 

FIG.  33. — COEFFICIENTS  FOR  CAST-IRON  PIPES.     (Coffin.) 


240  HYDRA  ULICS. 

The  diagram  Fig.  33  is  taken  from  Coffin.*  It  is  slightly  modi- 
fied from  the  -one  given  by  Smith,  the  dotted  lines  being  interpolated 
by  Coffin.  This  diagram  probably  represents  the  best  available  infor- 
mation on  the  subject,  but  for  large  sizes  and  for  very  small  sizes  it 
must  be  considered  as  rather  uncertain.  For  practical  use  also,  the 
diagram  is  somewhat  inconvenient,  as  it  will  frequently  happen  that 
both  v  and  c  are  unknown,  the  head  being  the  known  factor.  In  this 
case  the  problem  must  be  solved  by  making  two  or  three  successive 
approximations. 

A  formula  which  has  been  used  extensively  for  cast-iron  pipes  is 
the  Darcy  formula.     It  is 

v  =         '          MTs (29) 


where  a  and  ft  have  the  following  values  for  English  units : 

For  new  cast-iron  pipes         a  =  .00007726;  ft  =  .00000647. 
For  old  or  rough  iron  pipes  a  =  .0001545  ;     ft  =  .00001294. 

It  is  to  be  noted  that  the  values  of  these  constants  for  old  pipes  are 
taken  just  double  those  for  new  pipes,  which  results  in  giving  for  a 
particular  velocity  double  the  loss  of  head  in  the  former  case  as  in  the 
latter.  Darcy's  formula  was  derived  from  experiments  on  compara- 
tively small  pipes,  and  it  is  probably  true  that  for  large  pipes  and  high 
velocities  it  gives  somewhat  too  small  values  for  the  velocity.  Levy 
has  modified  Darcy's  formula  slightly,  but  the  modification  is  too  small 
to  be  of  any  practical  consequence. 

Instead  of  using  a  variable  coefficient  it  has  been  proposed  by  some 
to  adopt  a  formula  of  the  form  v  =  crnsm.  This  is  in  some  respects  a 
more  convenient  form  of  expression  than  the  Chezy  formula,  and  for 
any  particular  class  of  pipes  it  can  be  made  to  fit  the  experiments  quite 
as  well.  Two  formulas  of  this  class  deserve  mention,  that  of  Lampe" 
and  that  of  Flamant.  f  Lampe's  formula  is,  in  English  units, 

s/  =  77.68aT-694,r555, (30) 

where  d  =  diameter  of  the  pipe  and  s  —  slope.  Flamant,  after  making 
a  thorough  examination  of  all  available  experiments,  proposes  the  fol* 
lowing  formulas :  J  For  cast-iron  pipes  slightly  incrusted,  such  as  would 
nearly  always  be  the  case  after  a  few  years  of  service, 

v  =  ?6.28dW, (31) 

*  The  Graphical  Solution  of  Hydraulic  Problems.     New  York,  1897. 
t  For  discussion  of  recent  formulas  of  this  type  see  Eng.  News,  1901,  XLVI. 
p.  98 ;  Eng.  Record,  1903,  XLVII  ,  pp.  321,  667. 

|  Annales  des  Fonts  et  Chausse'es,  1892,  n.  pp.  301-350. 


COEFFICIENTS  AND   FORMULAS  FOR   CAST-IRON  PIPES.        241 


and  for  new  cast-iron  pipes 

v  =  86.3&/V (32) 

Besides  the  above  formulas  and  sets  of  coefficients,  Kutter's  for- 
mula for  c  (given  in  Art.  282)  is  frequently  applied  to  pipes,  although 
derived  from  experiments  on  open  channels.  The  value  of  n  is  taken 
according  to  the  nature  of  the  surface,  it  being  usually  assumed  about 
.Oil  for  smooth  pipes. 

264.  Comparison  of  Various  Formulas. — In  the  following  table  a 
brief  comparison  is  made  of  various  formulas. 

TABLE   NO.  46. 

COMPARISON   OF    VARIOUS    FORMULAS    FOR  THE   FLOW   OF  WATER   IN   SMOOTH   PIPES. 


Diam. 
in 
Inches. 

Slope. 

Velocities  in  Feet  per  Second. 

Smith. 

Lampe. 

Flamant. 

Darcy. 

K  utter. 

New  Pipe. 

Pipes  in 
Service. 

New  Pipe. 

Rough 
Pipe. 

•i 

.004 
.05 

.20 

1.07 

4-54 
9.68 

1.05 
4-25 
9.17 

1.02 
4-34 
9-59 

0.90 

3.83 
8.46 

1.20 
4.24 
8.47 

0.85 
3-00 
5-99 

0.79 

2.78 
5-57 

<i 

.001 
.01 
.1 

I.OO 

3.67 

12.80 

1.04 
3-73 
13-38 

1.02 

3.80 
14-13 

0.90 

3-35 
12.47 

1.18 
3-72 
11.77 

0.83 
2.63 
8.32 

0.96 
3-12 
9-85 

••! 

.0005 
.005 
.025 

1.  08 

3.96 

9.56 

1.14 
4.11 
10.03 

1.  12 

4.18 
IO.5I 

0.99 
3.69 
9.27 

1.22 
3-86 
8.64 

0.86 

2-73 
6.  n 

1.14 
3-73 
8-35 

36  j 

.0001 
.001 
.01 

1.  01 

3-57 
12.60 

T.OO 
3-60 
12.92 

0.98 
3-66 
13.64 

0.87 
3.23 
12.03 

0-97 
3-07 
9.72 

0.68 
2.17 

6.87 

1.  06 
3.62 
11.50 

H 

.00005 
.0005 

.005 

I.OI 

3-5i 
12.50 

0.97 

3-49 
12.54 

0-95 
3-55 
13.22 

0.84 

3.13 
11.66 

0.89 
2.82 
8.92 

0.63 
1.99 
6.31 

1.04 

3-57 
11.45 

An  examination  of  the  table  shows  that  the  results  by  Smith's 
diagram,  by  the  formula  of  Lampe",  and  by  Flamant 's  formula  for  new 
pipes  all  agree  very  closely.  Flamant's  formula  for  pipes  in  service 
gives  velocities  about  10  per  cent  lower  than  Smith's  diagram.  The 
loss  of  head  would  be  about  20  per  cent  higher.  Darcy 's  formula 
gives,  in  the  case  of  pipes  of  large  size,  results  considerably  below  the 
others.  Kutter's  formula,  on  the  other  hand,  gives  relatively  low 
results  for  small  pipes. 


242  HYDRA  ULICS. 

265.  Diagram  Recommended  for  Use  in  the  Design  of  Distributing 
Systems. — Among  the  various  formulas   mentioned,  that  of  Flamant 
for  cast-iron  pipes  in  service  is  considered  to  be  the  most  suitable  for 
use  in  the  design  of  ordinary  distributing  systems.     It  gives  a  slight 
margin  of  safety,  which,  in  case  the  pipes  are  properly  coated,  will 
probably  cover  the  deterioration  for  ten  or  fifteen  years.     This  formula 
has  the  further  advantage  of  being  easily  solved  by  the  use  of  loga- 
rithms, and  can  also  be  readily  solved  graphically.     The  diagram  on 
page  243,  constructed  after  the  principles  laid  down  by  M.  Lalanne 
and  M.  Daries,*  is  based  on  this  formula.      It  is  very  simple  and  offers 
little  chance  for  error.     On  the  four  vertical  lines  are  shown  the  four 
quantities,   discharge,   diameter,   loss  of  head  or  slope,   and  velocity. 
The  intersections  of  any  straight  line  with  these  four  vertical   lines 
indicate  corresponding  values  of  these  four  quantities ;  so  that  any  two 
being  given,  the  other  two  are  determined  by  the  application  of  a 
straight-edge,  t 

In  the  case  of  the  design  of  large  and  important  conduits  no  formula 
should  be  accepted  without  question,  but  a  special  investigation  of  the 
matter  of  coefficients  should  be  made.  Much  aid  in  estimating  values 
for  such  coefficients  will  be  obtained  from  the  extensive  Table  No.  I 
of  Trautwine's  translation  of  Ganguillet  and  Kutter,  which  contains  a 
large  collection  of  data  of  experiments,  and  calculated  values  of  c 
and  n. 

266.  Effect  of  Age  of  Service  on  Loss  of  Head. — In  the  diagram 
recommended  for  use  some  10  per  cent  reduction  of  velocity,  or  about 
20  per  cent  increase  in  head,  has  been  allowed  for  slight  deterioration 
of  the  pipe.      In  some  cases  this  would  doubtless  be  sufficient  to  cover 
a  period  of  ten  or  even  twenty  years,  while  in  other  cases  it  would 
undoubtedly  be  too  small   an    allowance.      Uncoated    cast-iron  pipe 
becomes  very  badly  tuberculated  within  ten  years  or  less,  and  the 
reduction  in  carrying  capacity  of  such  pipe  has  been  shown  by  experi- 
ments to  be  very  great, — 75  per  cent,   or  more,  in  the  case  of  4-  and 
6-inch  pipe.    Properly  coated  cast-iron  pipe,  such  as  is  universally  used 
at  the  present  time,    corrodes  very  much  less  rapidly.      Many  cases 
have  been  reported  of  tar-coated  pipe  which  has  remained  perfectly 
clean  and  bright  for  twenty  or  thirty  years.      On  the  other  hand,  there 
is  ample  evidence  that  tar-coating  does  not  always  entirely  prevent  the 
formation  of  tubercles.     The  extent  of  this  action  is  doubtless  influ- 

*  Nouvelle  Annals  de  la  Construction,  Aug.  1897,  XLIII. 

t  See  also  logarithmic  diagram  based  on  Levy's  formula  in  Eng.  News,  1899, 
XLii.  p.  4.  The  Hazen- Williams  slide  rule  is  a  very  convenient  device  for  such  calculations. 
It  is  based  on  the  formula  v  =  cd'™  r54. 


DIAGRAM 


CALCULATING    CAST-IRON  PIPES. 


20-^ 

—9000 

72- 

.03  — 

.7- 

I 

—8000 

66- 

.04  — 

"" 

_ 

—7000 

60- 

.OS  — 

&~ 

—6000 

54- 

.o6-i; 

.9- 

—5000 

48- 

-°83 

- 

10- 

42  — 

Pi!~ 

1- 

9- 

-4000 

I 

- 

.1  - 

8- 

36- 

~ 

7  _ 

*™ 

o  _E 

^~ 

/ 

-3000 

" 

6- 

30- 

- 

.3- 

28  - 

.3  — 

5  — 

26  - 



.4- 

— 

^-2000 

24- 

. 

.5- 

4- 

22- 

.5  — 
.6  •— 

.6 

_ 

20- 

.7- 

T3 

18- 

•8~E 

^                           •*- 

§       E 

-                  3 

16- 

01 

1                                  -,'9- 

u         1 

-1000^ 

14- 

!          i 

I        f!" 

Q-    2  — 

—900     g_ 

t,                           to* 

o>          I 
* 

—800     » 

—              c 

12- 

.c                             2 

J              i*: 

0 

2 

3     - 

—700    ^ 
—600    ° 

10- 
9- 

.S-                               3  — 

0, 

«8                          4~ 

^                                   ?.6- 

.s                   ^n 

r«                                         C  .8  - 

C 

?* 

*"                                  5  — 

1                                                                       *» 

—500     & 

8- 

6  — 

X                                  -^      - 

&1.0- 

—            {g 

)  — 

<a  .9- 

-400    | 

7- 

.^                                 8^ 
Q                              g/\~= 

£.4- 

o     o 

U)     * 

5 

|O  — 

.6- 

P   .7- 

-300 

6- 

.8  = 

4- 

.6- 

— 

5- 

^0J 

.5- 

M 

M 

- 

.4- 

^-200 

4— 

[30  — 

5- 

— 

40  — 

— 

50  — 

•»•= 

3  — 

60^ 

6- 

H 

80  -E 

rioo 

100-f 

.?^ 

—90 

™  I 

-80 

2- 

"" 

A      ~ 

—70 

200-^ 

o~ 

-60 

300  — 

Q~2 

^— 

-50 

L5-1 
400  — 

ID-1 

FIG.  34. — DIAGRAM  FOR  CALCULATING  CAST-IRON  PIPES. 


244  HYDRA  UL1CS. 

enced  by  the  quality  of  the  water,  but  unless  the  contrary  is  known  it 
will  be  necessary  to  assume  that  more  or  less  incrustation  will  take 
place.  Mr.  FitzGerald  reports  that  tar-coated  pipe  laid  in  Boston  will 
become  tuberculated  in  ten  or  fifteen  years.  In  some  cases  consider- 
able organic  growth  has  become  attached  to  the  interior  surface  of  the 
pipe,  and  this  acts  greatly  to  reduce  the  carrying  capacity. 

Tuberculation  or  incrustation  affects  the  carrying  capacity  of  a  pipe 
in  two  ways:  first,  it  reduces  the  cross-section,  and,  second,  it 
increases  the  roughness  of  the  pipe.  The  total  effect  on  velocity  will 
be  very  much  greater  in  small  pipes  than  in  large  pipes.  Compara- 
tively few  reliable  experiments  have  been  made  on  old  tar-coated  pipes, 
most  of  the  experiments  on  old  pipes  being  on  the  uncoated  pipe. 
Forbes  *  found  in  an  eighteen-year-old  tar-coated  pipe  14  and  16  inches 
in  diameter  a  value  of  c  equal  to  from  90  to  93,  about  25  per  cent  less 
than  for  new  pipe.  Experiments  by  FitzGerald  t  on  a  48 -inch  pipe 
sixteen  years  old  (tar-coated)  gave  a  value  of  c  =  108  (n  =  .014). 
The  value  of  c  for  this  same  pipe  when  new  was  140  to  144.  The 
velocity  in  the  old  pipe  was  thus  about  24  per  cent  less  than  in  the  new 
pipe. 

Of  the  various  formulas  for  old  pipes,  that  of  Darcy  has  probably 
been  the  most  frequently  used.  As  already  noted,  it  simply  gives  twice 
the  loss  of  head,  or  seven-tenths  the  velocity,  as  for  new  pipe. 
Mr.  E.  B.  Weston  suggests  a  series  of  coefficients  whereby  the  increase  in 
loss  of  head  due  to  age  is  placed  at  about  16  per  cent  each  five  years  over 
what  it  is  at  the  beginning,  but  no  allowance  is  made  for  differences  in 
size  of  pipe.  Coffin  has  constructed  a  diagram,  based  upon  experiments 
on  old  pipes,  which  gives  an  increase  in  loss  of  head  for  increase  of 
service  of  15  to  25  per  cent  for  each  five  years  for  ordinary  velocities 
of  2  to  5  feet  per  second.  The  effect  is  made  greater  the  greater  the 
velocity.  Some  indication  of  the  effect  of  age  on  riveted  pipes  will  be 
found  by  a  study  of  Table  No.  48,  page  246. 

267.  Friction  Loss  in  Service-pipes. — The  diagram  on  page  243  is 
not  suitably  arranged  for  calculating  sizes  of  small  pipes  such  as  are 
used  for  service  connections;  and  furthermore,  since  service-pipes  are 
usually  made  of  lead  or  of  galvanized  iron,  they  are  little  subject  to 
corrosion,  and  the  velocity  which  might  be  obtained  from  the  diagram 
would  be  rather  low.  For  the  design  of  such  pipes  Smith's  coefficients 
given  in  the  diagram  of  Fig.  33  will  give  results  sufficiently  close  for 
all  practical  purposes,  although  for  pipes  less  than  I  inch  in  diameter 

*  Jour.  New  Eng.  W.  W.  Assn.,  1892,  VI.  p.  164. 
\ Trans.  Am.  Soc.  C.  E.,  1896,  xxxv.  p.  241. 


COEFFICIENTS  FOR  RIVETED    PIPES, 


245 


the  results  are  probably  somewhat  too  low.  Table  No.  47  is  calcu- 
lated from  these  coefficients.  For  very  smooth  pipes,  such  as  those  of 
lead  or  brass,  Mr.  E.  B.  Weston  proposes  the  following  formula  for 
the  friction  factor /of  eq.  (27): 

0.0315  —  o.o6d 
f =0.0126+-       2-p ,      ....     (33) 

\  V 

in  which  the  foot-unit  is  to  be  used.  Tables  based  on  this  formula  are 
given  in  Weston 's  "  Friction  of  Water  in  Pipes."  This  formula  gives 
velocities  somewhat  greater  than  Smith's  coefficients. 

TABLE   NO.   47. 

LOSS   OF   HEAD   IN   SMALL   PIPES. 


u 

V 

£-inch  Diam. 

i-inch  Diam. 

i^-inch  Diam. 

2-inch  Diam. 

si-inch  Diam. 

3-inch  Diam. 

yj 

£ 

ill 

u 

&|| 

1J 

Ill 

rt.22 

•O~            4J* 

s  % 

E£fc 

**M  ai   O 

£s| 

s°s 

•a"    « 

rt       D 

V        V 

fll 

LI 

fll 

L! 

| 

fljL 

§u 

«5R 

|fa" 

|Si 

°£     2 

111 

*3£8 

18  S. 

Ju 

lo£ 

°  t<     M 

1 

Q 

a 

5 

5    8. 

Q 

5  s- 

Q 

o      w 
>J     o. 

Q 

a 

Q 

5  S. 

2.5 

.82 

9.8 

•  35 

T  e    a 

27 

OO     T 

ii 

•3.  7 

1.61 

8.2 

I.OI 

14.7 

.72 

1  j  •  j 

'56 

Z.  Z,  *  1 

*  •_ 

•*•  2 

2 

3     I 
4.9 

II  .O 

1.67 

*-^    i 
19.6 

1.  19 

30.  7 

.92 

AA    2 

76 

24 

1-53 

IO.OO 

6.1 

3-87 

I3.8 

2.44 

24-5 

1-73 

38.3 

1.36 

55-2 

.  /w 
1.  12 

3 

1.84 

14.2 

7-4 

5-33 

16.6 

3-37 

29.4 

2-39 

46.0 

1.88 

66.2 

i-55 

2.15 

17.7 

8.6 

6.95 

19-3 

4-44 

34-3 

3-14 

53.7 

2.47 

77-3 

2.  02 

4 

2-45 

22.4 

9.8 

9-31 

22.  I 

5.56 

39-2 

3-98 

61.3 

3.13 

88.3 

2.56 

44 

2.76 

27.6 

II.  0 

10.9 

24.8 

6.89 

44.1 

4.91 

69.0 

3.85 

99-4 

3-14 

5 

3-06 

33-3 

12.3 

12.3 

27.6 

8-33 

49.1 

5  94 

76.7 

4.66 

110.4 

3.81 

3-37 

39-7 

13-5 

15.5 

30.4 

9.88 

53-9 

6.42 

84.3 

5-53 

121.4 

4-52 

6 

3-68 

46.7 

14.7 

18.2 

33-1 

ii.5 

58.8 

8.22 

92.0 

6.45 

132-5 

5.27 

64 

3.98 

54-2 

15.9 

20.9 

35-9 

13-3 

63.8 

9.51 

99.6 

7.46 

143.5 

6.10 

7 

4.29 

62.6 

17.2 

24.0 

38.6 

15-2 

68.6 

10.8 

107.3 

8.53 

154.6 

7.01 

74 

4.60 

7L3 

18.4 

28.9 

41.4 

17.3 

73.6 

12.4 

115-0 

9.70 

165.6 

7-93 

8 

4.90 

80.8 

19.6 

32-7 

44.2 

19.5 

78-5 

13-9 

122.6 

10.9 

176.6 

8.94 

84 

5-21 

90.6 

20.9 

36.9 

46.9 

21.9 

83.4 

15.6 

130.3 

12.2 

187.7 

10.00 

9 

5-51 

101.6 

22.  I 

41.2 

49-7 

24.4 

88.3 

17.3 

138.0 

13-6 

198.7 

ii.  i 

94 

5.82 

112.9 

23.3 

45-9 

52.5 

27.2 

93-2 

19-3 

145.6 

209.7 

12.3 

10 

6.13 

124.8 

24-5 

48.0 

55-2 

30.2 

98.1 

21.3 

153-3 

16^6 

220.8 

13-7 

268.  Coefficients  for  Riveted  Pipes. — The  friction  loss  in  riveted  pipes 
depends  upon  the  thickness  of  the  plates  and  the  manner  of  making 
the  joints.  Experiments  on  this  class  of  pipes  are  not  sufficiently 
numerous  to  enable  any  general  expression  to  be  formulated,  so  that 
in  the  design  of  such  pipes  the  selection  of  coefficients  must  be  made 
by  reference  to  the  experimental  data.  In  general  it  is  found  that  the 
coefficient  c  changes  little  with  change  in  diameter  or  velocity,  and  in 
this  respect  exhibits  considerable  difference  from  its  variation  in  cast- 


246' 


HYDRA  ULICS. 


iron  pipe.  For  ordinary  velocities  the  value  of  c  for  new  pipe  appears 
to  range  between  100  and  115.  Probably  a  value  of  1 10  would  be  as 
great  as  should  be  used  in  almost  any  case.  Kutter's  formula  for  c  is 
very  often  used,  the  value  of  n  being  taken  equal  to  .013  to  .015. 

To  aid  in  the  selection  of  a  coefficient,  all  the  most  important 
experiments  on  large  riveted  pipe  are  given  in  Table  No.  48.  Further 
data  regarding  these  experiments  will  be  found  in  the  various  publica- 
tions referred  to.  The  table  is  mostly  taken  from  a  similar  one  given 
in  the  paper  by  Profs.  Marx,  Wing,  and  Hoskins  in  Trans.  Am.  Soc. 
C.  E.,  1898,  vol.  XL.  p.  471. 

TABLE   NO.  48. 

VALUES   OF   THE   COEFFICIENT   C  FOR    RIVETED   PIPES. 


1  Number  of 
Experiment. 

1  Diameter  of  Pipe 
in  Inches. 

Velocities  in  Feet  per  Second. 

I.O 

t.5 

2.0 

2-5 

3-o 

3-5 

4.0 

4-5 

s.o 

5-5 

6.0 

Values  of  Coefficient  c. 

I 
2 

3 
4 

6 

8 
9 

10 

ii 

12 

13 
14 

15 
16 

17 
18 

19 

20 
21 

II 
14 
15 
16 

24 

33 
35 
36 
36 
38 
38 
42 
42 
42 
48 
48 
48 
48 
72 
72 
103 

110.6 
123.6 

IIO.O 

108.5 

in.  6 

94-9 
103.7 
105.2 

87 

in.  6 

117.2 
106.3* 

no.  8 

108.4 

112.  0 

94-4 
103.7 
105.1 

104.7 

120.4 

no.  2 

108.5 
in.  7 
94-7 
103.7 
105.2 

105.0 

1  10.  0* 
II4.O 

78.5* 

123.2* 
no.  6 

126.8* 
107.0 

86 

90.8 

95-2 

99.4 

103.3 

II6.6* 

109.2* 

112.  8 

107.8 
113-2 
94.0 
104.0 
104.2 
in 
103.8 
106.2 

in.  8 
108.2 
112.4 
94.2 
103.7 
104.7 

104.3 
105.6 

II5.9* 
III.O 

105.5 

III.  2 
92.4 
104.9 

101.6 

1  08 
101.3 
108.8 

112.  6 

106.4 

112.  8 

93-o 

105.3 

IO2.2 

108 
102.4 

107.7 

II3.0 
107.2 
II3-4 

93-2 
104.8 
103.6 

JIO 

103.2 

106.9 

96.0 

IOI.O 
IOI.2 

78.0 

97.2 
97.1 

110 

81.6 
116.6 

103.0 
102.8 

105.4 

84.6 

100.8 

98.7 
in 
92.0 
112.7 

107.9 
104.3 
108.8 
89.6 

103-3 
100.3 
no 
98.0 
110.3 

*  Most  of  the  values  in  the  table  were  obtained  from  plotted  curves.      Those 
marked  with  an  asterisk  are  from  single  observations  and  are  inserted  in  the  table 
under  the  velocity  corresponding  most  nearly  with  the  observed  velocity. 

The  following  is  a  brief  description  of  the  experiments  the  results  of. 
which  are  tabulated  above: 

Nos.  i  and  3.  By  Hamilton  Smith,  North  Bloomfield,  Cal.  Sheet  iron 
with  taper  joints;  asphalt  and  tar-coating;  5  years  old. 

No.  2.  By  A.  McL.  Hawks.  Cylinder-joints;  asphalt  coating.  Tested 
when  3  years  old,  and  also  when  6  years  old  with  same  results.  Trans.  Am. 
Soc.  C.  E.,  1899,  XLII.  p.  155. 


FRICTION  LOSS  IN    WOOD-STAVE  PIPE.  247 

No.  4.  By  A.  L.  Adams.  Astoria  pipe-line.  Cylinder-joints;  asphalt 
coating;  new  pipe.  Trans.  Am.  Soc.  C.  E.,  1896,  xxxv.  p.  226. 

No.  .5.  By  Geo.  W.  Rafter  on  the  old  Rochester  conduit.  Cylinder- 
joints;  14  years  old.  Trans.  Am.  Soc.  C.  E.,  1891,  xxvi.  p.  20. 

Nos.  6,  7,  and  12.  By.  I.  W.  Smith  on  the  Portland  conduit.  Cylinder- 
joints;  asphalt  coating;  new  pipe.  Trans.  Am.  Soc.  C.  E.,  1891,  xxvi. 
p.  203. 

Nos.  8  and  9.  By  Clemens  Herschel  on  the  conduit  of  the  East  Jersey 
Water  Company  from  Belleville  to  South  Orange.  No.  8  made  with  new 
pipe;  No.  9  with  pipe  4  years  old.  Cylinder-joints;  asphalt  coating. 
Herschel's  "115  Experiments."- 

Nos.  10  and  n.  By  Kuichling  on  different  sections  of  the  Rochester 
conduit.  Cylinder-joints.  The  section  of  pipe  in  experiment  No.  10  was 
coated  partially  with  asphalt  and  partially  with  the  Sabin  coating.  Average 
plate  thickness  =  .27  inch.  Section  in  experiment  No.  n  coated  with  Sabin 
coating;  average  plate  thickness  .31  inch.  Age  of  pipes  about  i-J  years. 
These  same  sections  gave  in  November  and  December,  1898,  coefficients  of 
112.9  and  105.9  respectively.  Annual  Reports  of  Executive  Board  of 
Rochester,  1895-98. 

Nos.  13  to  1 8.  Experiments  by  Herschel.  No.  13,  Kearney  extension 
of  the  East  Jersey  Water  Company's  pipe-line.  Taper  joints;  new  pipe; 
coating  "  unusually  smooth."  No.  14,  on  conduit  No.  2  of  the  East  Jersey 
Water  Company;  new  pipe.  No.  15,  on  conduit  No.  i;  cylinder-joints; 
asphalt  coating;  new  pipe.  Nos.  16  and  17,  on  portions  of  the  same  conduit 
as  No.  15,  but  4  years  later.  No.  18,  on  portion  of  conduit  No.  2;  taper 
joints;  new  pipe.  "115  Experiments. " 

No.  19.  Experiments  by  Marx,  Wing,  and  Hoskins  on  the  conduit  of 
the  Pioneer  Electric  Company,  Ogden.  New  pipe;  butt-joints;  asphalt 
coating.  Trans.  Am.  Soc.  C.  E.,  1898,  XL.  p.  471. 

No.  20.  Same  as  No.  19,  but  2  years  later.  Proc.  Am.  Soc.  C.  E., 
Feb.  1900,  p.  1 08. 

No.  21.  By  Herschel  on  Holyoke  flume.  Cylinder- joints;  paint  coating 
washed  off;  rather  rusty.  ''115  Experiments." 

269.  Friction  Loss  in  Wood-stave  Pipe. — Very  few  experiments  have 
been  made  on  this  class  of  pipes.      Such  information  as  is  available  is 
collected  in  the  paper  by  Marx,  Wing,  and  Hoskins,  already  referred 
to,  in  which  are  also  described  some  experiments  by  the  authors  on  the 
Ogden  /2-inch  wooden-pipe  line.     The  few  experiments  made  previous 
to  these  indicated  a  value  of  n  in  Kutter's  formula  of  about  .010  for 
1 8-  to  3O-inch  pipes.     The  experiments  on  the  Ogden  pipe-line,  however, 
gave  a  value  of  c  varying  generally  from  1 1 5  to  125 ;  (n  =  .014  —  .013). 
Experiments  by  Noble  on  44-  and  54-inch  pipes  gave  values  of  c  equal  to 
110—115  (»==  .013)  for  the  44-inch, and  of  115—129  (n  =  .013  —  .012) 
for  the  54-inch  pipe.     Velocities  ranged  from  3.5  to  4.8  feet  per  second  in 
the  former  case  and  from  2.3  to  4.7  feet  per  second  in  the  latter  case.* 

270.  Measurement  of  Flow  through  Large  Pipes.— The  quantity  of 
water  flowing  through  pipes  may  be  measured  by  means  of  weirs  or 

*  Trans.  Am.  Soc.  C.  E.,  1902,  XLIX.  p.  143. 


248  HYDRAULICS. 

orifices,  or  by  noting  the  rate  of  filling  of  a  reservoir,  or  by  the  use  of 
meters.  In  Chapter  XXIX  various  kinds  of  meters  are  described 
and  discussed  with  particular  reference  to  their  use  on  service-pipes. 
For  accurately  measuring  the  quantity  of  water  flowing  through  large 
pipes,  as  in  the  making  of  tests,  probably  the  best  form  of  meter  is  the 
Venturi.  This  meter  simply  consists  of  a  contracted  section  of  pipe, 
AB,  Fig.  35,  with  pressure-gauges  at  A  and  C.  If  vl  and  v2  are  the 


FIG.  35.  —  VENTURI  METER. 

velocities  at  A   and   C,  h^  and  h2  the  pressures,  al  and  a2  the  areas, 
then,  neglecting  friction,  we  have,  from  eq.  (26),  page  226, 


(34) 


But  if  Q  =  theoretical  discharge,  then  vl  =  —  and  v2  =  —  . 


Substituting  and  reducing,  we  have 

^)-       '     •     •  (35) 


If  q  =  actual  discharge,  then  q  =  cQ,  where  c  is  a  coefficient  deter- 
mined by  experiment  and  nearly  equal  to  unity.* 

271.  Minor  Losses  of  Head.  —  Loss  of  Head  at  Entrance.  —  This  is 
expressed  by  the  formula 

'  *-&-•&  .......  <*» 

where  v  =  velocity  in  the  pipe,  and  c  is  the  coefficient  of  discharge  of 
a  short  tube  having  the  same  form  as  the  end  of  the  pipe.  For  various 
forms  at  entrance  we  have  the  following  values  : 

i-  1. 

Pipe  projecting  into  reservoir  ........  72  .93 

End  of  pipe  flush  with  reservoir  ......  82  .49 

Conical  or  bell-shaped  mouth  ........  93  to  .98     .15  to  .04 

*  See  paper  by  Herschel  on  Venturi  Meter,  Trans.  Am.  Soc.  C.  E.,  1887,  xvn. 
p.  228. 


MINOR   LOSSES   OF  HEAD.  249 

272.  Loss  Due  to  Sudden   Enlargement. — This    is    given    by  the 
formula 

'»> 


in  which  a^  and  a2  are  the  cross-sections  of  the  smaller  and  larger  pipes 
respectively,  and  v2  is  the  velocity  in  the  larger  pipe. 

273.  Loss  Due  to  Sudden  Contraction. — This  is  given  by 

\c!          j  2gt 

in  which  c'  depends  on  the  ratio  of  the  two  diameters  and  is  given  by 
Merriman  as  follows: 

Ratio  of  smaller  to  larger  diameter.  ...      o    .2       .4       .6      .8         i.o 

c' 62    .63     .64    .67     .72       i.o 


274.  Z^JJ  #/"  Head  at  Bends  *  is  equal  to  h  =  » —     ....     (39) 

for  a  90°  bend,  in  which  n  has  the  following  values  according  to  the  ratio 
of  the  radius  of  pipe  r  to  the  radius  of  curvature  R  ( Weisbach) : 

•g i       -2       .3       .4       .5       .6       .7       .8         .9       i.o 

# 13     .14     .16     ,21     .29     .44     .66     .98     1.41      1.98 

275.  Loss  of  Head  in  Valves. — Weisbach's  experiments  on  small 

vz 
gate- valves  gave  values  for  n  in  the  expression  h  =  n —  as  follows  :j- 

Ratio  of  height  of  opening  to  diameter .  .      $       }       f       \      f      J     J- 
Values  of  n 07   .26  .81    2.1    5.5    1798 

In  applying  the  above  formula  v  is  the  velocity  in  the  pipe. 

For  a  throttle-valve  placed  at  various  angles  B  with  the  axis  of  the 
pipe,  Weisbach  found  the  following  values  of  n\ 

6...      5°       10°      20°       30°      40°       50°       60°       65°       70° 
«...    .24      .52       1.5       3.9       n        33       118       256      750 

Experiments  on  large  gate-valves  have  been  made  by  Kuichling 
and  by  J.  W.  Smith.  The  following  table  gives  values  of  the  coefficient 
c  in  the  expression  Q  =  cA  V2gk  as  deduced  by  Kuichling  from  these 
two  sets  of  experiments.  J  In  this  expression  A  is  the  area  of  the 
opening,  h  is  the  head  lost  in  the  valve,  Q  is  the  rate  of  discharge. 

*  Williams  found  that  for  large  pipes  the  total  resistance  in  a  90°  bend  increased 
with  increased  radius  of  bend  beyond  four  or  five  pipe  diameters.  The  total  resistance 
in  a  length  of  pipe  of  80  diameters  (including  a  90°  bend)  of  moderate  radius  was 
found  to  be  from  20  to  30  per  cent  in  excess  of  the  same  length  of  straight  pipe. 
(See  his  valuable  paper  in  Trans.  Am.  Soc.  C.  E.,  1902,  XLVII.  p.  i.) 

t  See  values  for  4-in.  valves  in  Eng.  News,  1902,  XLVII.  p.  302. 

J  Trans.  Am.  Soc.  C.  E.,  1895,  xxxiv.  p.  243. 


250 


HYDRAULICS. 


.05 

.10 

•23 

.36 

•48 

.60 

•7i 

.81 

.89 

1-7 

I.O 

.72 

..70 

•  77 

.92 

i.2 

1.6 

1.2 

•9 

•83 

.82 

.84 

.90 

1.05 

i-35 

2.1 

TABLE   NO.  49. 

COEFFICIENTS    FOR   LARGE   GATE-VALVES. 

Ratio  of  height  of  opening    ) 

to  diameter  f  " 

Ratio  of  area  of  opening  ) 

to.  total  area  f  ' ' 

Coefficient  c  for  24-inch  valve. . 
Coefficient  c  for  3O-inch  valve. . 

Experiments  at  the  Ohio  State  University  in  1899  on  various  kinds 
of  small  valves  showed  that  gate-valves  when  wide  open  gave  a  coeffi- 
cient of  discharge  equal  to  from  .5  to  .7,  and  globe- valves  usually  from 
.3  to  .4-* 

276.  Hydraulics  of  Fire-streams. — Table  No.  50  contains  data  per- 
taining to  the  loss  of  head  in  fire-hose,  and  the  character  of  fire-streams 
under  different  pressures  and  for  different-sized  nozzles.  The  data  are 
taken  from  much  more  extensive  tables  given  by  Freeman  in  his 
elaborate  paper  on  the  hydraulics  of  fire-streams,  t 

TABLE   NO.  50. 

HOSE  AND    FIRE-STREAM    DATA. 


"o 

i-inch  Smooth  Nozzle. 

i|-inch  Smooth  Nozzle. 

ij-inch  Smooth  Nozzle. 

f 

c 

_0 

u 

£ 

c  § 

orK 

c 

|| 

^.h 

§1 

a 

_© 

§, 

*•* 

1*8 

C   0 

"N 
o 

15 
r^ 

u 

£  £ 

1          . 

M"N 

15 
O 

8,1 

^fe 

rt  "N 

"rt 

sj 

-C  n-] 

go  ^ 

rt  JJ 

harge  in  ( 
r  Minute. 

of  Head 
et  of  Ord 
>se. 

.SftS 

1) 

imum  Ho 
stance  fo 
re-streami 

sl 

^2 

<u  > 

'11 

K 

of  Head 
et  of  Ord 
>se. 

•5.0 

imum  Ho 
stance  for 
•e-streams 

eme  Droj: 
vel  of  No 

li 

jg  u 

•0*2 
So 

5s 

5  o 

i! 

0  0  | 

•8! 

I|I 

1? 

<cs 

J2  a 

|£B 

tt  o£ 

4)H-i  U) 

8S£ 

w  0. 

<"£ffi 

'§££ 

S5S 

U    1) 
X  ^ 

o  £ 
.52  a 

"feffi 

^  )—  j  "t^ 

*3^ 

cu 

Q 

1.4 

SS 

CL) 

3 

iJ 

is 

W 

Q 

•J 

> 

li 

13 

Ibs. 

Ibs. 

ft. 

ft. 

ft. 

Ibs. 

ft. 

ft. 

ft. 

Ibs. 

ft. 

ft. 

ft. 

20 

132 

5 

35 

37 

77 

168 

8 

36 

38 

80 

209 

12 

37 

40 

83 

30 

161 

7 

51 

47 

109 

206 

12 

52 

50 

115 

256 

19 

53 

54 

119 

40 

1  86 

10 

64 

55 

133 

238 

16 

65 

59 

142 

296 

25 

67 

63 

148 

50 

208 

12 

73 

61 

152 

266 

20 

75 

66 

162 

331 

31 

77 

70 

I69 

60 

228 

15 

79 

67 

167 

291 

24 

83 

72 

I78 

363 

37 

85 

76 

186 

70 

246 

17 

85 

72 

179 

314 

28 

88 

77 

191 

392 

43 

81 

200 

80 

263 

20 

89 

76 

189 

336 

32 

92 

81 

203 

419 

49 

95 

85 

213 

90 

279 

22 

92 

80 

197 

356 

36 

96 

85 

214 

444 

55 

99 

90 

225 

100 

295 

25 

96 

83 

205 

376 

40 

99 

89 

224 

468 

62 

101 

93 

236 

The  range  and  quality  of  fire-streams  has  recently  been  studied  by 
photography  by  Prof.  Marston.  His  results  for  i-inch  and  ij-inch 
smooth  nozzles  are  shown  in  the  diagrams  on  page  251.  The  paths 


*  Eng.  Record,  1899,  XL.  p.  78. 
f  Trans.  Am.  Soc.  C.  E.,  1889,  xxi.  p.  303. 


HYDRAULICS  OF  FIRE-STREAMS. 


251 


Pressure   per  Sq.  In.  at  Base  of   Play  Pipe 

Pressure  '1o*  Pressure    2O*  Pressure    30* 

75 


i-| 


25&   jv!    O        IOO  75  50  25  O         IOO  75 

*-••          Horizontal      Distance    -  Feet. 


50  25 


Pressure     4O* 


Pressure  per  Sq.  In.  at  Base  of   Play  Pipe. 


Pressure  5O# 


Pressure    JO* 


Horizontal      Distance    -   Feet. 

l^   INCH      SMOOTH      NOZZLE. 

Pressure  per  Sq.  In.  at  Base  of  Play  Pipe 

75 


THE  ENaiNtcmiMi  RECOUP. 


Pressure    20* 


Pressure    30* 


•00  75 


f9  ~>vy  £J  w 

izontal      Distance     -  Feet. 

Pressure  per  Sq.  in.  at  Base  of   Play  Pipe. 
Pressure    4O*  Pressure    SO# 


Horizontal      Distance     •  Fee' 
I    INCH       SMOOTH     NOZZLE. 


/  £xtr*m*  Drops        A 
frteman's  Experiments  Pf afreet  thus.-\  fair  ftre  Stream,     x 

(  Ovad  ftre  Stream.  » 


FIG.  36. — FIRE-STREAM  DIAGRAMS. 

(From  Engineering  Record,  Feb.  18,  1899.) 


252  HYDRA  ULICS. 

of  the  streams  are  shaded  for  pressures  of  30  pounds  or  above, 
wherever  a  solid  stream  was  shown  by  the  negative.  Beyond  the 
limits  indicated,  the  slightest  breeze  would  break  up  the  stream  badly. 
The  results  of  Freeman's  experiments  are  also  given  on  the  diagrams. 
The  pressures  in  Marston's  experiments  were  measured  at  the  base  of 
the  play-pipe,  and  varied  from  the  effective  pressure  at  the  orifice  from 
—  I.I  to  -{-  1.7  pounds  per  square  inch.  Experiments  were  also  made 
on  smooth  nozzles  of  |-  and  -J-inch,  and  on  ring  nozzles  of  i-inch  and 
i  J-inch  diameter.  The  ring  nozzles  gave,  in  general,  streams  of 
slightly  less  range  than  the  smooth  nozzles. 

277.  Friction   Loss   in  Fire-hydrants. — Experiments  by  M.   C.    L. 
Newcomb  at  Holyoke,  Mass. ,  on  twenty-one  different  kinds  of  hydrants 
showed  that  with  a  discharge  of  500  gallons  per  minute  the  loss  of  head 
was  in  nearly  all  cases  between  I  and  2  pounds  per  square  inch,  the 
maximum  being  2.5   pounds,  and  the  minimum  .8  pound.      In  many 
cases  the  greater  portion  of  the  loss  of  head  occurred  in  the  nozzle  and 
shows  the  necessity  of  making  the  passages  in  hydrants  of  large  size 
and  in  curved  lines.* 

278.  Water-hammer. — When  a  volume  of  water  flowing  in  a  pipe 
has  its  velocity  rapidly  checked  by  the  closing  of  a  valve  or  otherwise, 
a  pressure  is  developed  in  excess  of  the  static  pressure.      If  the  action 
is  very  sudden,   the   pressure   will   be  very  great,    particularly   if  the 
velocity  is  high  and  the  pipe  of  great  length.     This  effect  in  general  is 
called  water-hammer. 

The  estimation  of  the  amount  of  excess  pressure  due  to  water- 
hammer  in  a  pipe  system  is  a  matter  of  difficulty,  but  all  engineers 
admit  that  some  allowance  must  be  made.  Where  the  conditions  are 
definitely  known,  such  as  the  size  and  length  of  pipe,  and  the  rate  and 
manner  of  closing  a  valve,  it  is  quite  possible  to  compute  the  pressure 
with  a  considerable  degree  of  accuracy.  The  actual  problem  is,  how- 
ever, greatly  complicated,  due  partially  to  the  irregularity  in  form  and 
arrangement  of  the  pipes,  but  chiefly  to  a  lack  of  exact  knowledge  with 
respect  to  the  movement  of  the  valves,  pump-plungers,  or  whatever 
may  be  the  cause  of  the  trouble.  It  is,  however,  possible  to  gain  from 
theoretical  considerations,  and  from  experiments,  a  knowledge  of 
certain  general  laws  with  respect  to  water-hammer,  and  to  indicate 
certain  limits  to  the  pressure  which  may  be  produced  by  it.  The 
results  of  special  experiments  carried  out  under  certain  given  conditions 
may  also  be  studied  with  advantage. 

279.  Theoretical   Considerations. — The    greatest    possible    water- 

*  Trans.  Am.  Soc.  M.  E.,  1899,  xx.  p.  494. 


WA  TER-HA  MMER.  2  53 

hammer  will  be  caused  in  any  particular  case  when  a  valve  is  closed 
so  quickly  as  to  be  practically  instantaneous.  In  this  case  the  resulting 
pressure  is  a  function  involving  the  elasticity  of  the  water  and  of  the 
pipe,  and  is  a  case  of  impact  of  an  elastic  prism.  If  the  elasticity,  of 
the  pipe  be  neglected,  which  may  be  done  for  ordinary  sizes,  the  pres- 
sure of  impact  has  been  shown  to  be 

/  =?  -TT  .......  •  •  (40) 

in  which  v  =  initial  velocity  of  water  ; 

Ew  =  modulus  of  elasticity  of  water 

=  300,000  pounds  per  square  inch;  and 

V  =  about  4700  ft.  per  second,  =  velocity  of  sound  in  water. 
Substituting  the  values  of  Ew  and  F,  we  have,  in  pounds  per  square 
inch,  where  v  is  in  feet  per  second, 

/  =  64z;  .........      (41) 

The  pressure  developed  is  thus  proportional  to  the  velocity  of  the 
water  and  is  independent  of  the  length  of  the  pipe. 

Mr.  Frizell  *  has  derived  the  following  expression  for  the  pressure, 
in  which  account  is  taken  of  the  elasticity  of  the  pipe  : 


+   /   '    EP 

in  which  EP  —  modulus  of  elasticity  of  pipe  ; 
2r  =  diameter  of  pipe  in  feet;  and 

/  =  thickness  of  pipe  in  inches. 

These  formulas  are  valuable  as  indicating  the  maximum  possible 
limit  of  the  water-hammer.  The  question  arises,  however,  as  to  what 
constitutes  a  sudden  stoppage  of  the  water.  According  to  Mr.  Frizell 
the  closing  of  a  valve  is  essentially  instantaneous  if  the  time  of  closing 
is  less  than  the  time  necessary  for  the  wave  of  pressure  to  be  trans- 
mitted to  the  end  of  the  pipe  and  back,  at  the  rate  of  about  4700  feet 
per  second.  The  length  of  pipe  is  thus  seen  to  enter  into  the  problem 
of  water-hammer  by  affecting  the  definition  of  the  word  *  sudden.  '  In 
long  pipes,  therefore,  the  operation  of  the  valves  in  a  way  similar  to 
that  customary  for  short  pipes  would  be  likely  to  cause  a  much  greater 
water-hammer;  and  in  very  long  pipes  a  severe  hammer  might  be 
experienced  even  though  the  operation  were  relatively  slow. 

The  other  case  to  be  considered,  the  one  in  which  the  stoppage  of 
the  flow  is  not  sudden,  is  the  more  usual  problem,  but  at  the  same  time 
*  Trans.  Am.  Soc.  C.  E.,  1898,  xxxix.  p.  i. 


254  HYDRA  ULJCS. 

one  more  difficult  of  treatment.  The  pressure  developed  in  this  case 
is  simply  a  function  of  retardation  and  of  the  static  head ;  and  if  the 
manner  of  operating  a  valve  is  precisely  known,  the  pressure  can  be 
computed.  If  a  valve  is  closed  at  a  uniform  rate,  the  pressure  will  be 
a  maximum  at  the  end  of  the  movement,  and  with  similar  laws  of 
closing  the  pressure  will  be  approximately  proportional  to  the  length 
of  the  pipe,  to  the  speed  of  closing  of  the  valve,  and  to  the  velocity  of 
the  flow.  A  lower  maximum  pressure  will  be  experienced  if  valves 
are  so  arranged  as  to  close  rapidly  during  the  first  part  of  the  move-, 
ment  and  slowly  at  the  last.* 

280.  Experiments  on  Water-hammer. — Experiments  on  water-ram 
have  usually  been  made  by  determining  the  pressures  developed  in 
certain  short  lines  of  pipe  by  the  sudden  closing  of  a  gate-valve,  the 
pressure  being  measured  by  means  of  a  gauge.  Experiments  by  Mr. 
E.  B.  Weston  at  Providence,  R.  I.,t  on  small  pipes,  by  the  method 
described,  gave  results  which  approached  well  towards  the  theoretical 
maximum  given  by  eq.  (40).  The  ram  was  practically  proportional 
to  the  velocity  of  the  water. 

Experiments  by  Prof.  Carpenter  on  2-inch  pipes  gave  results  which 
are  shown  in  the  diagram  of  Fig.  3/4  The  curve  for  the  experiments 
without  air-chamber  shows  values  of  pressure  from  one-half  to  two- 
thirds  of  those  obtained  by  the  use  of  Mr.  Frizell's  formula,  eq.  (42). 
The  pressure  here  appears  to  increase  somewhat  more  rapidly  than  the 
velocity.  The  effect  of  air-chambers  is  very  marked. 

Experiments  at  Dartmouth  College  in  1 898  §  indicated  that  the 
force  of  water-ram  varies  with  the  velocity,  with  the  speed  of  the  clos- 
ing of  the  valve,  and  with  the  volume  of  water  in  the  pipe.  It  is  also 
greater  when  dead  ends  are  "located  near  the  valve.  Extensive  experi- 
ments have  been  carried  out  still  more  recently  in  Russia,  the  results 
of  which  go  to  confirm  the  general  laws  expressed  by  the  formulas  of 
Art.  279.  These  experiments  have  also  led  to  the  general  statement 
that  the  pressure  caused  by  a  sudden  decrease  in  velocity  is,  for  each 
foot  per  second  of  such  decrease,  approximately  4  atmospheres  (60 
pounds  per  square  inch)  for  small  pipes  and  3  atmospheres  (45  pounds 
per  square  inch)  for  large  pipes.  ||  These  values  are  very  nearly  the 
same  as  would  be  obtained  from  eq.  (42). 

*  For  a  theoretical  discussion  of  the  pressures  developed  when  valves  are  closed 
slowly,  together  with  results  of  some  experiments  with  slowly  moving  valves,  see 
Trans.  Assn.  C.  E.  of  Cornell  University,  1898,  p.  31.  See  also  a  paper  by  Prof, 
I.  P.  Church  in  the  Journal  of  the  Franklin  Inst.,  April  and  May,  1890. 

f  Trans.  Am.  Soc.  C.  E.,  1885,  xiv.  p.  238. 

\  Trans.  Am.  Soc.  M.  E. ,  1894,  xv.  p.  510.     Eng.  Record,  1894,  xxx.  p.  173. 
.  News,  1898,  xxxix.  p.  186.  ||  En.g.  News,  1900,  XLIV.  p.  So. 


WA  TER-HAMMER. 


255 


281.  Practical  Conclusions.  —  From  the  foregoing  discussion  the 
extreme  limits' of  water-hammer  are  approximately  indicated,  and  it 
would  appear  that  the  general  laws  are  to  some  extent  quite  definitely 
known,  from  both  theoretical  and.  experimental  considerations.  In 
simple  cases  of  the  operation  of  valves  it  is  easy  to  determine  from 
these  considerations  what  are  the  necessary  precautions  to  be  taken.  In 
many  cases  in  practice  the  difficulty  arises  from  causes  not  easily  traced, 
and  undoubtedly  the  effect  of  hammer  is  often  greatly  increased  by  the 
setting  up  of  vibrations  due  to  some  synchronous  action  of  the  pumps 
or  other  machinery,  accompanied  by  the  collection  of  air  in  the  pipes. 


7 


VELOCITY  IN  PIPE,  FT.  MR  IECOND. 


FIG.  37. — EXPERIMENTS  ON  WATER-RAM  BY  CARPENTER. 

To  prevent  excessive  water-hammer  from  the  closing  of  valves  it 
is  only  necessary  so  to  design  them  that  they  cannot  be  closed  very 
suddenly,  or  if  they  are  closed  suddenly  they  should  be  so  arranged 
that  the  velocity  in  the  adjacent  main  shall  not  exceed  a  moderate  limit 
of  8  to  12  inches  per  second  at  the  time  when  the  valve  is  operated. 
If  the  velocity  at  this  point  were  as  great  as  I  foot  per  second,  the 
maximum  possible  hammer  would  be  something  less  than  64  pounds 
per  square  inch,  according  to  eq.  (42).  The  operation  of  ordinary 
valves  in  a  distributing  system  can  scarcely  give  so  great  a  ram  as  the 
above.  Air-valves  and  pressure-relief  valves  should  be  so  proportioned 
that  any  sudden  reduction  of  velocity  caused  in  filling  or  operating 
a  pipe-line  shall  not  exceed  a  moderate  limit  such  as  above  speci- 
fied. The  closing  of  hydrant-valves  would  have  an  effect  depending 
upon  the  amount  by  which  the  velocity  of  water  in  the  adjacent  main  is 


256  •  HYDRAULICS. 

influenced  thereby.  Hydrants  attached  to  small  mains  will  thus  have 
a  greater  effect  than  when  attached  to  large  ones.  In  the  operation 
of  long  pipe-lines  at  high  velocities,  such  as  are  used  in  power  plants 
on  the  Pacific  coast,  special  precautions  must  be  taken  to  insure  a  very 
slow  movement  of  the  valves  ;  and  frequent  use  made  of  air-chambers 
and  relief-  valves.  It  has  been  found  that  to  check  the  pulsations  which 
are  caused  by  the  waves  of  pressure  set  up,  it  is  advantageous  to  use  air- 
chambers  which  are  single-acting,  that  is,  those  which  permit  water  to 
enter  readily  but  not  to  flow  out  rapidly.  In  a  distributing  system,  water- 
ram  is  sometimes  caused  by  the  action  of  the  pumps,  due  usually  to  a 
lack  of  capacity  in  the  air-chambers,  or  to  their  becoming  filled  with 
water.  The  effect  of  such  ram  upon  the  neighboring  pipes  is  frequently 
influenced  by  the  presence  of  dead  ends,  and  in  some  cases  trouble  of  this 
sort  has  been  removed  by  connecting  up  two  or  more  such  dead  ends. 

FLOW   OF   WATER    IN    OPEN   CHANNELS. 

282.  Formulas  Employed.  —  In  calculating  the  flow  of  water  in  open 
channels  the  Chezy  formula  (page  228)  is  used.  It  is 

v  =  c  Vrs, 
in  which  r  =  hydraulic  mean  radius  ; 

s  =  sine  of  the  slope  of  the  water-surface  ; 
c  =  a  coefficient. 

For  channels  similar  in  character  to  smooth  pipe  the  value  of  c  may 
be  taken  from  page  231. 

The  most  commonly  used  value  of  c  is  that  given  by  Kutter's 
formula,  which  was  derived  from  a  study  of  a  large  number  of  experi- 
ments. It  is, 

1.81  0.0028 


O.OO2»\ 
1  + 


•(41.65  + 


in  which  n  is  a  coefficient  of  roughness.     The  following  are  the  values 
of  n  usually  assumed  for  the  various  surfaces  mentioned :  n 

Channels  of  well-planed  timber , 009 

44          44  neat  cement  or  of  very  smooth  pipe oio 

44      .    V  unplaned  timber  or  ordinary  pipe 012 

44          "  smooth  ashlar  masonry  or  brickwork 013 

**          4<  ordinary  brickwork 015 

44          "  rubble  masonry 017 

44         in  earth  free  from  obstructions O2O  to  .025 

14         with  detritus  or  aquatic  plants 030 


FLOW  OF   WATER  IN  OPEN  CHANNELS. 


257 


In  formula  (43)  it  is  seen  that  the  value  of  c  is  made  to  vary  with 
r  and  also  with  s,  but  the  effect  of  a  change  in  s  for  all  but  those  cases 
in  which  the  slope  is  very  small  is  of  little  importance,  and  for  all  prac- 
tical purposes  in  the  design  of  sewers  and  water-conduits  a  constant 
value  of  s,  such  as  .001,  may  be  assumed.  Table  No.  51  gives  values 
of  c,  corresponding  to  various  values  of  r  and  of  n9  for  a  constant  value 
of  s  equal  to  .001. 


TABLE   NO.  61. 

VALUES    OF  C  IN    KUTTER'S    FORMULA   WHEN  S  =  O.OOI. 


in 


Values  of  «. 


Feet. 

.009 

.010 

.Oil 

.012 

.013 

.015 

.017 

.020 

.025 

.030 

.1 

108 

94 

82 

73 

65 

53 

45 

35 

26 

20 

.2 

129 

"3 

100 

89 

80 

66 

56 

45 

34 

26 

•  3 

142 

124 

III 

99 

90 

75 

63 

52 

38 

30 

•4 

150 

132 

118 

106 

96 

80 

69 

56 

42 

34 

•5 

157 

139 

124 

in 

101 

85 

73 

60 

45 

36 

.6 

162 

143 

128 

116 

105 

89 

76 

63 

48 

38 

•  7 

166 

147 

132 

119 

109 

92 

79 

65 

50 

40 

.8 

170 

151 

135 

122 

112 

95 

82 

68 

52 

42 

•9 

173 

154 

138 

125 

114 

97 

84 

70 

54 

43 

.0 

175 

156 

140 

127 

116 

99 

86 

7i 

,  55 

45 

.2 

1  80 

160 

145 

131 

120 

103 

89 

74 

58 

47 

•  4 

184 

164 

148 

135 

124 

1  06 

92 

77 

60 

49 

.6 

187 

167 

151 

137 

126 

108 

94 

79 

62 

51 

.8 

189 

169 

153 

140 

129 

no 

97 

81 

64 

53 

2.0 

191 

172 

155 

142 

130 

112 

98 

83 

65 

54 

2-5 

196 

176 

1  60 

146 

135 

116 

102 

86 

69 

57 

3-0 

199 

179 

163 

149 

138 

119 

105 

89 

71 

59 

3-5 

202 

182 

1  66 

152 

I4O 

122 

107 

91 

73 

61 

4.0 

204 

184 

168 

154 

143 

I24 

no 

93 

75 

03 

4-5 

206 

186 

170 

156 

144 

126 

in 

95 

77 

64 

5-0 

208 

188 

172 

158 

I46 

127 

H3 

97 

78 

66 

Values  of  c  from  gaugings  of  the  New  Croton  Aqueduct  and  of  the 
Sudbury  Aqueduct  are  represented  in  Fig.  38.*  The  conduits  are  of 
horseshoe  shape  and  are  brick-lined.  In  the  figure,  Kutter's  formula 
is  also  plotted  for  values  of  n  equal  to  .013  and  .014.  It  is  to  be  noted 
that  this  formula  gives  values  of  c,  as  compared  with  the  experiments, 
which  increase  too  rapidly  with  increase  in  r. 

The  adopted  curve  for  the  Stony  Brook  conduit  is  also  given.  The 
equation  of  this  curve  is  c  =  I22.6r°-57  Vs.  The  flow  in  the  new  Croton 
Aqueduct  is  closely  represented  by  the  equation  v  =  I24r*'&  V s.  t 

*  Eng.  News,  1898,  XL.  p.  n.  See  also  article  by  Patch  in  Eng.  News,  1902, 
XL vn.  p.  488  for  gaugings  of  Sudbury  and  Cochituate  aqueducts  and  effect  of  vege- 
table growth  on  flow.  t  Eng.  Record,  1895,  xxxn.  p.  223. 


HYDRA  ULICS. 


283.  Measurement  of  Water  Flowing  in  Open  Channels, — In  the  case 
of  small  channels  the  discharge  can  be  measured  by  means  of  a  weir 
specially  constructed  for  the  purpose,  which  should  comply  with  the 
conditions  already  noted  on  page  228.  The  discharge  of  large  streams 
may  often  be  obtained  by  noting  the  head  on  some  existing  dam  or 
weir.  Where  such  a  structure  does  not  exist,  then  the  discharge  may 
be  found  by  measuring  the  cross-section  at  a  suitable  place  and  deter- 
mining the  average  velocity  of  the  water  by  the  use  of  floats  or  by  a 


80 


100 


MO  I2CK          iJO 

Values  of  Coefr/cent  c. 
FIG.  38. — COEFFICIENTS  FOR  LARGE  CONDUITS 


150 


160 


current-meter.  The  latter  method  is  the  most  reliable.  Determina- 
tions of  discharge  having  been  made  at  various  stages  of  water,  a  dis- 
charge-curve can  be  drawn  and  subsequent  values  deduced  from  gauge 
records.  Reliable  work  of  this  kind  involves  the  consideration  of  many 
details  which  cannot  be  entered  upon  here  and  for  which  reference 
must  be  had  to  works  on  hydraulics  and  surveying. 

NOTE. — The  preceding  chapter  being  but  a  very  brief  abstract  of  the  more 
common  formulas  of  hydraulics  and  of  the  results  of  experiments,  no  attempt 
is  made  to  give  a  bibliography  of  the  subject  farther  than  is  done  by  the  foot- 
notes throughout  the  chapter.  These,  however,  will  enable  the  student  to 
refer  to  much  of  the  most  recent  information  on  the  subject.  For  further 
guide,  reference  should  be  made  to  such  special  works  as  Hamilton  Smith, 
and  Ganguillet  and  Kutter,  and  to  the  various  general  works  on  hydraulics. 


A.    WORKS  FOR  THE  COLLECTION  OF  WATER. 

CHAPTER   XIII. 
RIVER  AND   LAKE   INTAKES. 

284.  General  Conditions. — In  drawing  a  water-supply  from  a  natural 
body  of  water  there  are  certain  general  requirements  which  the  intake 
works  are   designed  to  meet.      First  in    importance    is   reliability  of 
operation,  as  a  failure  here  often  means  the  immediate  shutting  off  of 
the  entire  supply.      Another  important  requirement  is  that  the  point  of 
intake  should  be  so  located  as  to  obtain  water  of  the  best  available 
quality.      Provision   should   also  be  made  for  excluding  fish,   various 
floating  objects,  and  the  coarser  sediment,  such  as  sand  and  gravel. 
Finally,  the  construction  should  be  an  economical  one. 

Intake  works  consist  of  some  form  of  conduit  (pipe  or  tunnel) 
extending  out  to  the  selected  point  of  intake,  some  protective  works  at 
the  open  end  of  same,  and,  usually,  regulating-valves  and  screens  placed 
at  some  point  between  the  pumps  and  intake.  If  the  intake-pipe  is 
short,  it  may  be  merely  an  extension  of  the  suction-pipe  of  the  pumps ; 
but  where  it  is  long,  the  usual  practice  is  to  interpose  a  wet-well  of 
chamber  as  near  the  pumps  as  practicable  and  draw  therefrom,  long 
suction-pipes  being  disadvantageous. 

Varying  natural  conditions  give  rise  to  important  variations  in 
arrangement  and  form  of  structures,  and  these  will  now  be  briefly  dis- 
cussed. 

RIVER   INTAKES. 

285.  Location. — The  location  of  the  intake  must  be  selected  with 
reference  to  (i)  the  quality  of  the  water,  and  (2)  the  cost  of  construc- 
tion and  maintenance  of  the  works  connected  therewith  in  so  far  as  this 
is  affected  by  the  question  of  site.      As  regards  quality  the  question  of 
the  effect  of  the  pollution  from  other  cities  and  towns  higher  up  along 
the  stream,  and  the  question  of  the  general  suitability  of  the  source,  are 
here   supposed   to   have   been   already  considered  and  a   conclusion 

259 


260  RIVER  AND    LAKE   INTAKES. 

reached  in  accordance  with  the  principles  discussed  in  preceding 
chapters.  It  is  equally  important  that  the  precise  point  of  location  of 
the  intake  be  decided  upon  with  as  careful  consideration  of  these  prin- 
ciples. 

The  point  of  intake  should,  first  of  all,  be  free  from  local  sources 
of  pollution  and  should  therefore  be  located  above  all  sewer  outfalls  of 
the  town  in  question.  In  the  case  of  tidal  streams,  sewage-polluted 
water  may  be  carried  long  distances  above  the  respective  outfalls  at 
flood  tide,  and  before  selecting  the  location  careful  study  should  be 
made  of  this  question  by  means  of  floats  and  by  examinations  of  the 
water  at  various  seasons  of  the  year.  Again,  it  will  often  be  found  that 
the  quality  of  the  water  is  quite  different  along  the  two  banks  of  a 
stream,  owing  to  near-by  sources  of  pollution  and  to  the  entrance  of 
tributary  waters.  The  location  of  the  intake  must  also  be  determined 
with  special  reference  to  the  lowest  water-stage. 

As  regards  the  structural  features,  the  points  to  be  considered  are: 
permanency  of  river-channel,  nature  of  river-bed  and  velocity  of  cur- 
rent, suitability  of  adjacent  ground  for  pumping-station  and  other 
works,  and  expense  of  conduit  construction  from  intake  to  pumps  and 
from  pumps  to  distributing  system.  In  the  case  of  a  stream  of  rapid 
fall  the  question  of  the  head  gained  by  going  farther  up-stream  would 
be  an  important  one. 

286.  Intakes  in  Large  Streams  Varying  Little  in  Stage. — These  are 
of  the  simplest  character.     The  water  may  usually  be  taken  from  near 
the  shore,  the  end  of  the  intake-pipe  being  supported  on  a  small  foun- 
dation of  concrete,  or  on  a  wooden  crib,  or  by  a  masonry  retaining- 
wall  in  the  case  of  large  works.      In  the  last  case  some  dredging  may 
be  required  in  front  of  the  intake,  and  also  wing  walls  built  to  retain 
the  sloping  bank.      Gate-  and  screen-chambers  may  also  be  made  a 
part  of  this  structure,  as  in  the  intake  at  Philadelphia  described  below. 

The  intake-pipes,  usually  of  cast  iron,  may  lead  directly  to  the 
pumps,  thus  acting  as  suction-pipes,  or  to  a  gate-chamber  and  wet-well. 
In  the  latter  case  the  suction-pipes  of  the  pumps  lead  from  this  wet- 
well.  Gratings  of  cast  iron  or  wood,  with  large  openings,  are  usually 
placed  at  the  entrance  to  the  intake  to  prevent  the  admission  of  large 
objects,  while  fish-screens  of  copper  of  relatively  fine  mesh  are  inserted 
in  the  gate-house  or  placed  over  the  ends  of  the  suction-pipes. 

287.  Examples. — The  Queen  Lane  intake  of  the  Philadelphia  water-works 
is  illustrated  in  Fig.  39.*     The  intake  here  is  divided  into  two  equal  parts, 
each  half  having  three  sluiceways  2.96  feet  by  4  feet,  provided  with  vertical 

*  Proc.  Eng.  Club  Philadelphia,  1897,  xm.  p.  245. 


RIVER  INTAKES. 


26l 


sliding-gates  at  the  outer  end.  Iron  screens  are  placed  in  front  of  the  gates 
and  held  in  place  by  masonry  walls  built  out  several  feet  from  the  face  of  the 
main  wall.  Two  48-inch  cast-iron  suction-mains  lead  from  each  division  of 
the  intake  to  the  pumps,  one  for  each  of  the  four  2O-million-gallon  engines. 
It  is  to  be  noted  that  these  suction-pipes  are  laid  somewhat  above  water-level 
and  therefore  any  leak  would  allow  the  entrance  of  air.  Considerable  trouble 
was  in  fact  experienced  from  this  cause,  and  it  was  not  entirely  overcome  by 
recalking  the  joints  and  coating  them  with  asphalt.  The  intake  was  con- 
structed inside  of  a  V-shaped  coffer-dam.  A  channel  45  feet  long  extending 
to  deep  water  was  excavated  in  front  of  the  intake. 


a  8  a 


Section   A  B 
FIG.  39. — QUEEN  LANE  INTAKE,  PHILADELPHIA. 


FIG.  40. — INTAKE  AT  HAMBURG,  GERMANY. 

In  Fig.  40  is  shown  the  intake  of  the  Hamburg,  Germany,  Water-works.* 
This  is  also  a  case  in  which  there  is  little  variation  in  river  stage,  and  the 
arrangement  adopted  is  simple  and  substantial. 


yter.    Das  Wasserwerk  der  freien  und  Hansestadt  Hamburg,  p.  14. 


262  RIVER  AND    LAKE  INTAKES. 

288.  Intakes  in  Streams  of  Ordinary  or  Great  Variation  in  Water- 
level. — In  this  case  it  usually  becomes  necessary  to  extend  the  intake- 
pipe  a  considerable  distance  from  the  banks  of  the  stream  in  order  to 
reach  a  suitable  location  at  low  water.  Then  in  order  to  enable  the 
pumps  to  reach  the  water  at  the  lowest  stage,  which  requires  them  to 
be  not  more  than  I  5  or  20  feet  above  that  level,  it  is  often  necessary 
to  place  them  in  a  deep  pump-pit  much  below  high- water  level.  The 
construction  of  a  water-tight  pit  for  this  purpose  is  then  an  important 
feature  of  the  works.  A  method  of  avoiding  this  expensive  feature  for 
temporary  works  consists  in  mounting  the  pumps  upon  a  car  which 
may  be  moved  up  or  down  an  inclined  track  built  on  the  river-bank. 
This  plan  was  in  use  for  several  years  in  the  old  St.  Louis  works. 

The  outer  end  of  the  intake-pipe  is  usually  protected  by  a  simple 
timber  crib  supporting  the  end  of  the  pipe  2  or  3  feet  above  the  river^ 
bottom,  and  held  in  place  and  protected  from  scour  by  broken  stone. 
A  coarse  screen  or  grating  is  ordinarily  placed  over  that  compartment 
of  the  crib  containing  the  intake-pipe.  It  is  desirable  to  have  the  total 
area  of  the  openings  of  this  grating  2  or  3  times  that  of  the  pipe  itself 
in  order  to  keep  the  entrance  velocity  low.  Sometimes  in  order  to 
strain  out  the  sediment  the  crib  is  entirely  filled  with  broken  stone  and 
sand  to  form  a  filter-crib  as  illustrated  in  Chapter  XIV. 

Another  form  of  construction  at  the  end  of  the  intake  is  a  masonry 
tower  extending  above  high  water  and  containing  ports  and  sluice- 
gates similar  in  form  to  those  used  in  reservoirs  (Chapter  XVI).  To 
provide  stability  against  ice  and  drift  the  tower  is  built  similar  to  a 
bridge  pier  in  form,  the  inlet  ports  being  placed  along  the  sides.  The 
arrangement  of  interior  compartments  and  gates  is  well  illustrated  by  the 
St.  Louis  intake  described  in  Art.  289.  Heavy  cast-iron  gratings  are 
bolted  to  the  walls  just  outside  the  ports.  The  size  of  ports  should  be 
sufficient  to 'keep  the  entrance  velocity  down  to  2  or  3  feet  per  second. 

The  tower  has  the  advantage  over  the  crib  construction  in  perma- 
nence and  reliability.  It  also  enables  the  water  to  be  drawn  from 
different  levels,  and  by  means  of  shut-off  valves  the  intake-conduit  can 
be  emptied  at  any  time  and  cleaned.  For  these  reasons  this  form  of 
construction  is  to  be  commended,  but  it  is  much  more  expensive  than 
the  crib  construction  and  is  therefore  suited  only  for  the  larger  and 
more  important  works. 

From  the  crib  or  inlet-tower  the  intake-pipe  usually  runs  to  a  wet- 
well,  the  end  of  the  pipe  being  placed  at  least  far  enough  below  low- 
water  level  to  give  the  head  necessary  for  overcoming  the  pipe  friction. 
It  is  also  desirable  that  the  pipe  should  be  placed  at  all  points  below 


niVER  INTAKES. 


263 


the  hydraulic  grade-line,  as  otherwise  it  will  act  as  a  siphon  and  require 
special  apparatus  for  removing  the  air  at  intervals.  From  the  wet-well 
the  suction-pipes  lead  to  the  pumps.  Provision  for  flushing  the  intake- 
pipe  may  be  made  by  connecting  it  through  a  by-pass  with  the  force- 
main  of  the  distributing  system. 

Instead  of  a  pipe,  a  tunnel  may  be  used  to  conduct  the  water  from 
tower  to  pumps,  short  vertical  shafts  connecting  therewith  at  either  end. 
This  form  of  construction  will  be  economical  only  in  the  largest  works, 
but  it  is  of  the  most  permanent  character. 

289.  Examples. — A  typical  arrangement  for  works  situated  along  a  stream 
of  wide  variation  is  that  at  Steubenville,  Ohio,  illustrated  in  Fig.  41.*  The 
intake  consists  of  two  24-inch  cast-iron  pipes  running  from  a  submerged  crib 
in  the  Ohio  River  to  a  wet-well  15  feet  in  diameter  and  30  feet  deep.  This 
well  has  a  shell  and  top  of  ^-inch  boiler-steel,  a  Portland-cement  bottom,  and 
brick  lining.  From  here  two  1 6-inch  suction-pipes  extend  through  a  tunnel 
to  the  pump-pit,  the  suction  never  being  greater  than  15  feet.  Provision  is 
also  made  for  a  third  suction-pipe  20  inches  in  diameter.  The  pump-pit  is 
far  below  high-water  level  and  is  thoroughly  water-tight,  as  is  the  tunnel  and 
well.  It  has  a  double  wall  with  a  filling  of  Portland-cement  mortar,  I  to  I. 
The  valves  in  the  wet -well  may  be  operated  either  from  above  or  from  the 
tunnel.  Messrs.  Wilkins  and  Davison,  Pittsburgh,  Pa.,  were  the  engineers. 


"Sglofk 

FIG.  41. — INTAKE  AT  STEUBENVILLE,  OHIO. 

The  general  arrangement  of  intake,  and  details  of  the  inlet-tower,  of  the 
St.  Louis  Water-works  are  illustrated  in  Fig.  42.  The  intake  here  is  located 
near  the  northern  city  limits  far  above  all  local  pollution  and  1500  feet  from 
the  shore.  The  exterior  masonry  of  the  tower  is  of  granite.  The  portion 
subjected  to  the  action  of  the  floating  ice  is  rough-pointed,  and  the  remainder 
is  quarry-faced.  The  interior  is  faced  with  limestone.  Four  inlets  lead  into 
the  north  chamber,  and  two  into  the  chamber  directly  over  the  intake-shaft, 
but  the  latter  are  not  ordinarily  used.  The  gates  are  operated  by  hydraulic 
cylinders.  The  screen-chamber  is  placed  on  shore  adjacent  to  the  wet-well, 
two  sets  of  screens  being  used  of  ^-inch  and  -£-inch  mesh  respectively. 
Unusual  difficulties  were  encountered  in  sinking  the  crib  for  the  inlet-tower 
on  account  of  the  rocky  bottom  and  the  very  swift  current  of  6  to  8  miles  per 
hour.  In  Fig.  43  are  shown  details  of  the  gates  of  the  inlet-tower,  f  These 
are  again  referred  to  in  Chapter  XVI. 


*  Eng.  Record,  1898,  XXXVIII,  p.  360. 

f  Eng.  News,  1891,  xxvi.  p.  4.     Eng.  Record,  1892,  XXV.  p.  319. 


264 


RIVER  AND   LAKE  INTAKES. 


The  new  Cincinnati  intake  furnishes  an  instructive  example  of  a  modern 
and  substantial  engineering  work.  It  is  shown  in  Fig.  44.  The  inlet-tower, 
on  account  of  the  shape  of  the  river-bed,  is  located  close  to  the  Kentucky 


Profile     of      Tunnel 
FIG.  42. — INTAKE  AT  ST.  Louis. 

shore.  It  is  quite  similar  in  general  design  to  that  at  St.  Louis.  The  tunnel 
is  lined  with  two  rings  of  brick  with  concrete  backing;  it  is  designed  for  a 
self -cleansing  velocity  of  3  feet  per  second.  A  peculiar  feature  is  the  very 
deep  pump-pit,  made  necessary  by  the  great  variations  in  river  stage  (about  70 


RIVER   INTAKES. 


265 


Section  7\B  Enlarged. 
FIG.  43.  —  GATE  DETAILS,  ST.  Louis  INLET-TOWER. 

.JSP: 


••§.  .Stratified,           J          Limestone  j 
_ « _..-. **IA.? I'M  ....-  c 


FIG.  44.  —  THE  CINCINNATI  WATER- WORKS  INTAKE. 

(From  Engineering  News,  vol.  XL.) 


266  RIVEK  AND   LAKE  INTAKES. 

feet).  The  upper  portion  of  the  uptake-shaft  is  lined  with  f-inch  steel  plates, 
and  this  lining  is  carried  up  through  the  pump-pit  as  a  steel  pipe  10  feet  in 
diameter.  The  suction-pipes  of  the  pumps  connect  with  this  shaft  near  the 
floor  of  the  pump-pit.  The  masonry  walls  are  4  feet  thick  at  the  top  an(J 
14. 5  at  the  bottom,  and  to  insure  imperviousness  a  |--inch  steel  shell  is  built 
into  the  wall. 

290.  Intake-works  for  Gravity  Supplies. — Where  a  stream  has  a 
rapid  fall  it  may  be  practicable  to  conduct  the  water  entirely  by  gravity 
through  a  canal  or  conduit  to  the  place  of  consumption,  or  perhaps  to 
filters  or  to  pumping-stations.    If  the  stream  is  small,  it  will  usually  be 
desirable  to  construct  a  low  dam  or  diversion-weir  impounding  a  small 
volume  of  water,  from  which  reservoir  the  conduit  may  lead.      A  gate- 
house  with  screens   and  controlling  gates  or  valves  is  placed  at  the 
entrance  of  the  conduit.      If  coarse  sediment  is  carried  by  the  stream, 
small  settling-basins  should  be  provided  near  the  head  of  the  conduit, 
or  the  reservoir  built  large  enough  to  act  as  such.      ^For  descriptions 
of  many   works   of  this   character   see   various   works   on    irrigation.) 
Where  the  stream  has  a  sandy  or  gravelly  bottom  it  may  be  practicable 
to  construct  filter-galleries  underneath  and  yet  be  able  to  convey  the 
water  entirely  by  gravity. 

In  Fig.  45  is  illustrated  the  small  diversion-weir  of  the  Simla, 
India,  Water-works.  The  stream  is  very  small,  and  the  weir  is  so 
arranged  that  only  the  dry-weather  flow  is  caught,  the  muddy  water 
of  the  floods,  which  flows  at  a  relatively  high  velocity,  leaping  the 
opening  and  passing  on.  A  somewhat  similar  arrangement  is  used  at 
Altona,  Pa.  There  the  flood-water  is  conveyed  in  an  artificial  channel, 
in  the  bottom  of  which  is  a  masonry  gutter  covered  by  a  grating  and 
connected  to  a  pipe  leading  to  the  reservoir.  The  gutter  and  pipe  are 
designed  for  a  maximum  capacity  of  50  million  gallons  per  day,  and 
any  flow  in  excess  of  this  must  pass  on  down  the  channel.  Less  can 
be  admitted  by  partly  closing  a  valve.* 

LAKE    INTAKES. 

291.  Location. — The  location  of  a  lake  intake  in  such  a  position  as 
to  obtain  at  all  times  water  of  the  best  quality,  and  to  fulfill  the  require- 
ments of  safety  against  interruption,  is  a  question  requiring  very  careful 
study.      In   a  lake   unpolluted   by  sewage   some  of  the   things   to  be 
investigated  are:  the  location  of  the  mouths  of  streams  and  the  sedi- 
ment carried  by  them ;  the  character  of  the  lake  bottom ;  the  direction 
of  wind  and  currents  and  their  effects  in  stirring  up  the  mud  on  the 

*  Jour.  New  Eng.  W.   W.  Assn.,  1899,  xiv.  p.  151. 


LAKE  INTAKES. 


267 


lake  bottom  and  in  conveying  sediment  from  point  to  point;  and 
matters  pertaining  to  the  quality  of  the  water,  such  as  temperature, 
color,  effect  of  stagnation,  etc.,  as  discussed  in  Chapter  IX.  (An 
investigation  of  this  character  carried  out  for  the  city  of  Syracuse  on 


FIG.  45.— DIVERTING-WEIR  OF  THE  SIMLA,  INDIA,  WATER-WORKS. 

(From  Proc.  Inst.  Civil  Engineers,  vol.  cxxxn.) 

Skaneateles  Lake,  a  body  of  very  pure  water,  involved  the  taking  of 
over  3000  soundings.) 

The  intake  should  if  practicable  be  located  at  a  sufficient  depth  to 
be  free  from  any  considerable  wave-action,  both  to  secure  greater 
stability  and  to  avoid  the  effect  of  the  disturbance  of  the  sediment  by 
the  waves.  It  was  shown  in  Chapter  IX  that  even  in  small  ponds  the 
wind  stirs  up  the  water  to  a  depth  of  15  or  20  feet,  so  that  this  may  be 
taken  as  about  the  minimum  depth.  A  greater  depth  is  desirable  if 
bad  effects  of  stagnation  are  not  present,  since  the  water  becomes 
rapidly  cooler  below  this  point.  In  large  lakes  the  wave-action 
extends  to  much  greater  depths  and  the  intake  should  be  extended 
accordingly  to  depths  of  40  or  50  feet.  In  such  large  bodies  of  water, 


268  RIVER  AND    LAKE   INTAKES. 

bad  odors  from  stagnation  are  little  to  be  feared.  Where  the  water  is 
shallow  for  a  long  distance  from  shore,  as  along  Lake  Michigan,  and 
especially  Lake  Erie,  the  best  length  of  intake-conduit  becomes  too 
great  to  be  afforded  by  any  but  the  largest  cities. 

Most  of  the  cities  along  the  Great  Lakes  dispose  of  their  sewage  by 
running  it  directly  into  the  lake  at  the  most  convenient  point ;  and  for 
those  places  that  draw  their  water-supply  from  the  same  body  of  water 
the  most  difficult  part  of  the  intake  problem  is  to  exclude  their  own 
sewage.  As  the  cities  grow,  the  intakes  are  pushed  farther  and  farther 
out,  but  usually  not  until  the  necessity  of  the  step  is  brought  home  by 
increased  mortality  from  typhoid  fever;  and,  however  carefully  this 
matter  is  followed  up,  the  quality  of  the  water  taken  from  such  sources 
must  always  be  looked  upon  with  suspicion.  In  Chicago  the  length  of 
intake  has  gradually  increased  to  4  miles.  In  Milwaukee  it  is  \\  miles, 
while  the  new  intake  at  Cleveland  is  about  5  miles  long. 

292.  The  Intake-conduit. — Whether  the  conduit  should  be  a  pipe- 
line or  a  tunnel  depends  upon  the  cost  of  construction  and  the  relative 
reliability  of  the  two  forms.  In  small  works  the  cost  of  a  tunnel  would 
be  prohibitory,  while  in  the  case  of  a  very  large  intake  a  tunnel  may 
be  the  cheaper.  Again,  a  pipe-line,  unless  sunk  very  deep,  is  subject 
to  disturbances  near  the  shore  end  by  ice  action,  wreckage,  and  scour 
from  storms.  The  best  solution  may  consist  of  a  combination  of  the 
two,  as  at  Milwaukee,  where  a  pipe  is  used  at  the  outer  end  and  a 
tunnel  at  the  shore  end. 

The  size  of  the  conduit  will  be  largely  controlled  by  the  permissible 
loss  of  head  from  intake  to  pumps,  and  this  in  turn  will  depend  upon 
the  available  depth  of  suction  and  upon  the  economy  of  construction 
of  conduit,  wet-well,  and  pump-pit.  In  very  long  intakes  this  will 
necessitate  low  velocities  and  large  sizes. 

The  methods  employed  in  executing  tunnel  work  are  similar  to 
those  in  other  cases  where  water  is  to  be  feared.  Excavation  is 
usually  carried  on  from  the  intake-shaft,  and  often  from  one  or  more 
intermediate  shafts  sunk  by  the  use  of  large  wooden  cribs  having 
interior  wells.  Soft  strata  are  penetrated  by  cast-iron  or  steel  linings, 
with  or  without  the  use  of  compressed  air  as  the  case  may  require. 

Submerged-pipe  intakes  are  usually  laid  by  the  aid  of  divers, 
although  other  methods  have  been  used.  The  pipe  is  preferably  laid 
in  a  dredged  trench,  at  least  as  far  out  as  wave-action  is  to  be  feared, 
and  should  be  covered  generally  to  a  depth  of  3  or  4  feet.  Near  the 
shore  end  the  covering  should  be  considerably  deeper  than  this.  In 
some  instances  the  pipe  has  not  been  covered,  but  held  in  place  by 


LAKE   INTAKES.  '26$ 

piling  or  by  special  anchor-cribs.  Various  methods  of  laying  sub- 
merged pipe  are  described  in  Chapter  XXIV.  Pipes  have  sometimes 
lifted  on  account  of  being  emptied  of  water,  but  this  is  unusual  and 
cannot  happen  if  the  shore  end  rises  above  the  submerged  portion  by 
an  amount  equal  to  the  diameter  of  the  pipe. 

Both  cast-iron  and  riveted  steel  pipe  have  been  used  for  intakes. 
Their  relative  advantages  depend  upon  durability,  convenience  in 
handling,  and  cost.  Steel  is  lighter  and  easier  to  handle,  but  at  the 
same  time  more  easily  disturbed  when  laid. 

293.  Protection-works.  —  The  greater  number  of  lake  intakes  are 
protected  by  submerged  cribs,  but  a  few  of  the  largest,  notably  those 
at  Chicago  and  the  new  intake  at  Cleveland,  have  large  exposed  cribs. 
All  these  protect  shafts  at  the  ends  of  tunnels.  Such  cribs  are  much 
more  expensive  than  submerged  ones  and  require  constant  attendance 
after  completion,  but  in  the  case  of  tunnel  intakes  an  exposed  crib  is 
necessary  in  the  construction  of  the  end  shaft,  and  to  make  it  perma- 
nent is  of  great  advantage  in  case  of  future  extensions.  It  also  enables 
water  to  be  drawn  at  different  levels.  On  the  whole,  however,  the 
economy  of  this  form  may  be  doubted ;  and  in  the  case  of  the  Cleve- 
land intake  a  submerged  crib  was  recommended  by  a  commission  of 
engineers,  consisting  of  Messrs.  Rudolph  Hering,  G.  H.  Benzenberg, 
and  Desmond  FitzGerald,  chiefly  on  the  grounds  of  expense  and  of 
trouble  with  ice.  Comparing  a  submerged  crib  with  an  exposed  one 
they  say:*  "A  submerged  crib,  on  the  other  hand,  say  10  feet  in 
height,  in  53  feet  of  water  allows  the  free  passage  of  ice  on  the  surface, 
and  uninterrupted  access  for  the  water.  In  a  lake  the  size  of  Lake 
Erie  stagnation  effects  would  hardly  occur  in  such  a  position,  and  the 
water  will  always  be  of  excellent  quality  near  the  bottom.  We,  there- 
fore, recommend  a  submerged  crib  for  the  intake."  Also :  "  It  is 
important  that  the  velocity  of  the  water,  where  it  enters  the  crib,  should 
be  reduced  to  but  3  or  4  inches  per  second,  and  that  the  area  of  ingress 
be  sufficient  to  produce  this  result.  The  evident  consequence  will  be 
that  less  floating  matter  will  be  drawn  into  the  crib."  In  a  report  on 
this  subject  to  the  city  of  Buffalo,  Mr.  E.  B.  Guthrie  recommends  the 
submerged  crib  on  practically  the  same  grounds. 

To  avoid  the  entrance  of  the  coarser  sediment  the  open  end  of  the 
intake  of  the  lower  port-holes  of  a  closed  crib  should  be  6  or  8  feet 
above  the  bottom  of  the  lake. 

294.    Obstruction  of  Intakes  by  Anchor-ice.  —  The  greatest  difficulty 

*  Abstract  of  report  in  Eng.  News,  1896,  xxxv.  p.  117. 


2/0 


RIVER   AND   LAKE  INTAKES. 


met  with  in  operating  lake  intakes  is  due  to  the  clogging  of  the  ports 
by  anchor  ice  or  frazil  ice.  Frazil  ice  consists  of  needles  of  ice  which 
form  in  open,  moving  water,  and  which  on  account  of  their  small  size 
are  readily  carried  below  the  surface  by  comparatively  weak  currents. 
Anchor  ice  forms  directly  upon  submerged  objects  in  shallow,  open 
water,  due  to  excessive  heat  radiation  such  as  occurs  on  cold,  clear 
nights.  Both  anchor  and  frazil  ice  are  apt  to  give  much  trouble  at  ex- 
posed cribs  and  shallow,  submerged  ones,  by  forming  upon  the  bars  of 
racks  and  port  holes,  and  especially  upon  surfaces  of  metal.  The 
trouble  is  met  in  various  ways.  The  most  effective  method,  where 
practicable,  is  the  use  of  steam,  as  a  very  small  rise  of  temperature  of 
the  exposed  surfaces  is  sufficient  to  overcome  the  difficulty.  Com- 
pressed air,  chains  drawn  back  and  forth  through  the  ports,  axes  and 
pike-poles  are  some  of  the  other  means  used.  Anchor  and  frazil  ice  do 
not  form  where  a  surface  sheet  has  formed. 

As  tending  to  obviate  the  difficulty  with  anchor-ice,  large  port  area 
and  deep  ports  should  be  used ;  and  in  the  later  cribs  this  feature  has 
been  observed,  the  ratio  of  area  of  ports  to  tunnel  being  about  four  in 
the  later  Chicago  cribs  and  eight  in  the  new  Cleveland  crib.  This  is 
of  equal  or  greater  importance  in  submerged  cribs.  In  this  connection 
note  the  recommendation  of  a  velocity  of  3  or  4  inches  per  second 
mentioned  in  the  preceding  article. 

Anchor-ice  is  often  formed  in  Northern  rivers  at  points  of  high 
velocity,  but  trouble  with  river  intakes  may  usually  be  obviated  by 


«x/2 


FIG.  46. — SUBMERGED  CRIB,  MILWAUKEE  INTAKE. 

(From  Engineering  News,  vol.  xxxiv.) 

locating  the  intake,  at  a  point  where  the  surface  will  readily  freeze  over. 
If  this  cannot  be  done,  then  measures  similar  to  those  employed  on  the 
lakes  must  be  adopted.  A  method  which  has  been  used  to  advantage 
in  dealing  with  anchor-ice,  and  one  which  is  applicable  to  intakes  near 
the  shore  of  streams,  small  lakes,  or  reservoirs,  is  to  create  a  quiet  body 
of  water  for  some  distance  around  the  inlet  by  means  of  a  raft  or  boom 
of  logs. 


LAKE  INTAKES. 


27I 


295.  Examples  of  Lake  Intakes. — It  has  already  been  mentioned  that  the 
Milwaukee  intake  consists  partly  of  tunnel  and  partly  of  cast-iron  pipe. 
At  the  junction  of  these  portions  is  placed  an  exposed  wooden  crib  with 
concrete  filling,  which  is  provided  with  emergency  inlets.  At  the  outer 
end  of  the  pipe-Hue  is  a  submerged  crib;  this  is  illustrated  in  Fig.  46.  The 
compartment  into  which  the  pipe  opens  is  covered  with  a  wooden  grating  of 
2  X  12-inch  planks  with  2-inch  spaces  between,  giving  200  square  feet  of 
opening,  or  about  ten  times  the  pipe  cross-section. 

Fig.  47  illustrates  the  new  2^-mile  crib  of  the  Chicago  Water- works.  It 
is  circular  in  plan  and  has  a  central  well  60  feet  in  diameter  with  a  timber 
floor  6  feet  thick.  The  bottom  20  feet  is  of  hemlock  timber,  and  above  this 
is  a  steel  shell  filled  with  concrete.  After  the  crib  was  sunk  in  place,  holes 


u 


Section 


Half  Sectional   Side  Elevation. 


FIG.  47.— NEW  2^-MiLE  INTAKE-CRIB,  CHICAGO. 

(From  Engineering  News,  vol.  XLII.) 


were  cut  through  the  timber  bottom  and  two  cast-iron  shafts  12  feet  in 
diameter  were  sunk  to  a  depth  of  61  feet,  below  which  the  lining  of  the  shaft 
is  of  brick.  Water  is  admitted  to  the  interior  well  through  eight  ports  6x6 
feet,  located  6  feet  above  the  lake  bottom  or  about  30  feet  below  the  water- 
surface,  and  at  that  depth  it  is  thought  that  trouble  from  anchor-ice  will  be 
avoided.  From  the  well  the  water  passes  into  each  shaft  through  three  gates 
4-J-  X  6  feet.  The  shafts  connect  with  lo-foot  tunnels.  The  superstructure 
of  the  crib  includes  quarters  for  the  attendants,  light- house,  boiler-  and 
engine-rooms,  etc.  The  total  cost  was  about  $200,000.* 


'••'  Eng.  News,  1899,  XLII.  p.  139. 


272  RIVER  AND   LAKE   INTAKES. 


LITERATURE. 

1.  Pearsons.     The  Water-works  of  Kansas  City.     Eng.  News,  1887,  xviu. 

P-  345- 

2.  The  Suction   and   Siphon    Pipe   of  the  Auburn,    N.    Y.,    Water-works. 

Eng.  News,  1890,  xxiv.  p.  387. 

3.  Feind.     The  New  Water-works    of  the  City  of  Chicago.     Eng.  News, 

1890,  xxiv.  p.  2. 

4.  The  Geneva,  N.  Y.,  Water-works.     Eng.  Record,  1891,  xxm.  p.  244. 

5.  The  New  Inlet-tunnel  and  Tower  of  the  St.  Louis  Water-works.     Eng. 

News,  1891,  xxvi.  p.  4;  Eng.  Record,  1892,  xxv.  p.  319. 

6.  Menominee  Water-works  Iron  Intake.     Eng.  Record,  1892,  xxvi.  p.  280. 

7.  Feind.     Chicago    New    Four-mile    Lake   Tunnel    and   its    Appendages. 

Eng.  News,  1892,  xxviii.  p.  236. 

8.  Water-works    Intakes   on    Lake   Michigan.      Eng.    News,    1893,    xxix. 

P-  555- 

9.  The  Falcon  Rotary  Strainer  for  Water-works  Inlets.     Eng.  News,  1893, 

xxix.  p.  309. 
10.  Submerged  Water-works  Intake  at  Burlington,  Vt.  Eng.  News,  1894, 

xxxi.  p.  512. 
•ii.  Cast-iron  Intake-crib  for  the  Water- works  of  South  Milwaukee,  Wis. 

Eng.  News,  1894,  xxxn.  p.  70. 

12.  Ericson.     The  Hyde  Park  or  68th  St.  Tunnel  Extension,  Chicago  Water- 

works.    Eng.  News,  1894,  xxxi.  p.  452. 

13.  Inlet-crib  and  Well,  Dunkirk  Water-works.     Eng.   Record,    1894,   xxx. 

p.  424. 

14.  The  Nashville,  Tenn.,  Water-works.     Eng.  Record,  1894,  xxx.  p.  305. 

15.  Hill.     The  Water-works  of  Syracuse,  N.   Y.     Trans.   Am.   Soc.   C.   E., 

1895,  xxxiv.  p.  23. 

1 6.  The  Washburn   Park  Water-works,    Minneapolis,    Minn.     Eng.   Record, 

1895,  xxxii.  p.  259. 

17.  The  Milwaukee  Water-works  New  Intake.      Eng.  Record,    1895,   xxxii. 

p.  112;  Eng.  News,  1895,  xxxiv.  p.  187. 

1 8.  A  Discussion  on  Anchor-ice.     Eng.  Record,   1895,  xxxi.   p.  206.      From 

Trans.  Am.  Soc.  C.  E.,  1894,  xxxii.  p.  278. 

19.  Brough.     Submerged  Cast-iron  Pipe  Intake  for  the  Water-works  of  Erie, 

Pa.     Eng.  News,  1895,  xxxiv.  p.  373. 

20.  Anchor-ice   Troubles  at   Ottawa,   Canada.       Eng.   Record,    1895,    xxxi. 

P-  134. 

21.  Studies  for  a  Water-works  Intake  at  Buffalo,  N.  Y.     Eng.  News,  1895, 

xxxni.  p.  309. 

22.  .The  New  Rochester  Water-works.     Eng.   Record,    1895,   xxxi.   p.   346; 

Eng.  News,  1895,  xxxm.  p.  234. 

23.  Smith.     Omaha,   Neb.,   City  Water-works.     Eng.  Record,    1896,   xxxiv. 

p.  483. 

24.  Coggeshall.     Anchor-ice.       Jour.    New  Eng.    W.    W.    Assn.,    1896,    x. 

p.  265. 

25.  Ward.      Prevention  of   Trouble   with  Anchor-ice.     Eng.   Record,    1896, 

xxxm.  p.  314. 


LITER  A  T  URE.  2  73 

26.  Hering,  Benzenberg,  and  FitzGerald.    Report  on  Improved  Water-supply 

and  Sewerage  Systems  for  Cleveland.     Abstract,  Eng.  News,   1896, 
xxxv.  p.  117. 

27.  The   Chicago   Water-works   Tunnel    Extension.       -Eng.    Recoid,    1896, 

xxxiv.  p.  257. 

28.  The  Newton,  N.  J.,  Water-works.     Eng.  Record,  1896,  xxxm.  p.   187. 

29.  Schulz.     The  New  Lake  Tunnel  and  Cribs  for  the  Cleveland,  O.,  Water- 

works.    Eng.  Record,  1897,  xxxv.  p.  535. 

30.  The  New  Water-works  Intake  Tunnel   for  Cleveland,   O.     Eng.  News, 

1898,    XL.    p.    82. 

31.  Progress  on  the  New  Water-works  for  Cincinnati,  O.     Eng.  News,  1898, 

XL.  p.  354;  Eng.  Record,  1898,  xxxvm.  p.  513. 

32.  Patton.     The    Municipal  Water- works   of.  the   City  of  Duluth,    Minn. 

Eng.  News,  1898,  xxxix.  p.  282. 

33.  The    Grafton,    W.    Va.,    Water-works.      Eng.    Record,    1898,    xxxvm. 

P-  539- 

34.  Barrally.     The  North  Tonawanda,   N.  Y.,  Water- works.     Eng.  Record, 

1898,  xxxvm.  p.  515. 

35.  The  Steubenville,  O.,  Water-works.     Eng.  Record,  1898,  xxxvm.  p.  360. 

36.  The   Chicago    Water-works   Extension   Tunnels.     Eng.    Record,    1898, 

xxxvii.  p.  538.- 

37.  New  Tunnels,   Intake-crib,   and  Pumping-stations,   Chicago,   111.     Eng. 

News,  1899,  XLII.  p.  139. 

38.  Flood-water  Channel,  Altona  Reservoir.     Eng  Record,  1899,  XL.  p.  386. 

39.  The  Water-supply  Tunnels  of  Chicago.     Eng.  News,  1900,  XLIV.  p.  259, 

ei  seq. 

40.  Spengler.     The  Water-works    System    of    Chicago.     Jour.    West.    Soc. 

Engrs.,  1901,  vi.  p.  279. 

41.  Hubbell.     Experience  with  Anchor  Ice  at  the  Detroit  Water-works  and 

Elsewhere.      Contains   bibliography.     Univ.    of    Michigan    Technic^ 
1903,  p.   17.     Eng.  News,  1903,  L.  p.  147. 

42.  Wall.     Ice  at  the  Intake  of  the  St.  Louis  Water-works.     Eng.  Record, 

1905,  LI.  p.  443. 

43.  The    New   Intake  of  the  Erie    Water-works.     Eng.  Record,   1905,  LII. 

P.  434- 

44.  The  Pittsburgh  Filtration  Plant;  River  Intake.     Eng.  Record,  1906,  LIV. 

p.  622. 

45.  Barnes.     Ice  Formation.     New  York,  John  Wiley  &  Sons,  1906. 


CHAPTER   XIV. 
WORKS  FOR  THE   COLLECTION   OF   GROUND-WATER. 

296.  Classification. — The  various  forms  of  works  built  for  the  collec- 
tion of  ground-waters  may  be  divided  into  the  following  classes: 

(1)  Works  for  utilizing  the  flow  of  springs; 

(2)  Shallow  wells,  including  ordinary  dug  wells  and  tubular  wells; 

(3)  Deep  and  artesian  wells. 

(4)  Horizontal  galleries  and  wells; 

WORKS   FOR    UTILIZING   THE   FLOW   FROM   SPRINGS. 

297.  Objects  to  be  Attained. — The  chief  objects  to  be  accomplished 
in  the  construction  of  works  of  the  kind  here  considered  are,  the  pro° 
tection  of  the  water  from  pollution  and  the  spring  from  injury  through 
clogging  or  otherwise,  the  furnishing  of  a  convenient  chamber  from 
which  the  conduit-pipes  may  lead,  and,  in  some  cases,  the  enlargement 
of  the  yield  by  suitable  forms  of  construction.      Besides  these,   other 
minor  objects  are  sometimes  provided  for,  according  to  the  necessities 
of  the  case,   such  as  gate-chambers,  settling-basins,  measuring-weirs, 
etc. 

298.  Ordinary  Forms  of  Collecting-basins. — If  a  supply  sufficient  at 
all  times  for  the   demand  can   be  obtained  from  one   or  more   large 
springs,  each  one  should  have  its  separate  basin  from  which  the  water 
maybe  conducted  to  a  common  main.     The  simplest  form  of  works 
consists  of  a  small  masonry  well  or  basin  surrounding  the  spring  and 
from  which  the  conduit-pipe  leads.      To  prevent  a  growth  of  vegetable 
organisms    and    consequent   deterioration    of  the    water,    such    basin 
should  always  be  covered  so  as  to  exclude  the  light.      For  a  small 
spring,  a  circular  well  covered  with  a  stone  cap  cemented  in  place  and 
provided  with  a  manhole  is  a  simple  and  effective  arrangement.     For 
larger  springs  a  masonry  vault  covered  with  2  or  3  feet  of  earth  is 
preferable.      If  the  spring  is  located  on  a  steep  hillside,  the  collecting- 

274 


COLLECTING-BASINS  FOR  SPRINGS. 


275 


chamber  is  conveniently  constructed  in  the  form  of  a  horizontal  gallery 
built  into  the  hill,  access  to  which  is  had  through  a  door  or  manhole. 

Overflow-pipes  leading  into  drains  or  open  channels  should  be  pro- 
vided for,  and  to  facilitate  cleaning  and  repairs  a  waste-pipe  with  valve 
may  also  be  put  in,  through  which  the  basin  can  be  emptied.  Gates 
or  valves  should  also  be  provided  in  the  conduit-pipe.  Weir-chambers 
with  suitable  floats  are  an  inexpensive  but  valuable  feature,  as  they 
enable  complete  records  of  the  yield  to  be  easily  obtained.  If  the 
water  carries  fine  sand  in  suspension,  the  basin  should  be  made  large 
enough  to  permit  this  to  settle. 

Mineral  and  other  springs  occurring  in  public  places  usually  have 
open  basins,  and  opportunities  are  offered  in  the  walls  and  parapets  for 
ornamentation. 

Examples. — In  Fig.  48  is  shown  a  simple  covered  basin.  It  is 
a  type  of  those  used  in  protecting  the  Vanne  supply  of  Paris.  The 


Secfiona)  Plan 
FIG.  48. — COLLECTING-BASIN,  VANNE  SUPPLY,  PARIS. 

ground  here  is  quite  level.  Fig.  49  shows  a  collecting-chamber  on  a 
side  hill  for  the  water-supply  of  the  city  of  Lahr.  It  contains  weir, 
settling-chamber,  conduit-pipe  with  strainer,  overflow-  and  waste- 
pipes.* 

*  Lueger.     Die  Wasserversorgung  der  Stadte,  p.  397. 


276 


WORKS  FOR    THE    COLLECTION  OF  GROUND-WATER. 


299.  Methods  of  Increasing  the  Flow. — If  the  natural  yield  of  a 
spring  is  insufficient,  it  will  sometimes  be  possible  to  increase  it.     The 
proper  form  of  collecting  works  to  accomplish  this  depends  upon  the 
character  of  the  spring.      It  will  be  here  convenient  to  treat  the  springs 
under  the  same  classification  as  in  Chapter  VII. 

300.  Springs  of  the  First  Class.  — In  this  class  the  water  appears 
at  the  upper  surface  of  a  stratum  of  impervious  material  overlaid  by  the 
water-bearing  deposit,  frequently  in  the  form  of  several  small  springs. 
Instead  of  dealing  with  each  one  individually  it  will  often  be  better  to 


Plan 

FIG.  49.— COLLECTING-BASIN,  CITY  OF  LAHR.     (Lueger.) 

construct  a  long  collecting-gallery  running  parallel  to  the  outcrop  and 
leading  to  a  central  collecting-chamber  which  can  be  made  similar  in 
form  to  that  for  a  large  spring.  This  gallery,  which  is  made  similar 
to  those  described  in  Art.  356,  should  be  built  deep  enough  to  rest  upon 
the  impervious  material,  and  thus  to  collect  all  the  underground 
flowage  as  well  as  that  appearing  as  springs.  The  total  yield  may  be 
thus  much  increased,  the  increase  being  relatively  greatest  during  dry 
weather. 

In  the  case  of  a  single  large  spring  the  flow  can  sometimes  be 
increased  by  opening  up  the  water-passages  for  some  distance  into  the 


THE   HYDRAULICS   OF   WELLS.  277 

hill,  thus  decreasing  the  resistance  to  flow  and  possibly  drawing  from 
a  larger  area.  Such  a  procedure  is  likely  at  the  same  time  to  make 
the  flow  more  irregular  by  drawing  more  rapidly  on  the  storage 
capacity  of  the  ground,  and  this  plan  should  hence  not  be  adopted 
without  careful  consideration. 

301.  Springs  of  the  Second  Class,   or  those  where  an  impervious 
layer  covers  to  a  greater  or  less  extent  the  water-bearing  stratum. — 
Such  a  spring  may  represent  but  a  part  of  the  ground-water  flow,  and  if 
borings  indicate  a  ground-water  stream  of  considerable  extent,  the  col- 
lecting-works may  be  arranged  without  much  reference  to  the  spring. 
Such  works  will  ordinarily  be  some  form  of  well  or  gallery  like  those 
described  in  subsequent  articles. 

In  the  case  of  one  of  the  springs  described  in  Art.  92,  page  104,  a 
well  was  sunk  near  by,  and  after  sealing  the  spring  the  water  rose  in 
the  well  3  feet  higher  than  before,  and  5  feet  above  the  surface  of  the 
adjacent  ground.  Extended  tests  indicated  considerably  increased 
yield  over  that  of  the  spring.  A  similar  spring  indicated  by  tests,  after 
the  construction  of  collecting-works,  an  average  yield  of  about  440,000 
gallons  per  day,  as  compared  to  an  average  previous  flow  of  275,000 
gallons.  In  this  case  the  "well  is  circular,  22  feet  in  average 
diameter,  24  feet  deep,  built  of  open-jointed  rubble  masonry  with  a 
lining  of  brick  laid  in  cement  mortar  for  the  upper  1 8  feet,  and  is  sur- 
mounted by  a  conical  shingle  roof.  It  was  built  at  the  largest  and 
highest  of  the  three  springs,  and  the  sites  of  the  other  two  were  sealed 
over  by  beds  of  concrete,  while  the  water  was  kept  down  by  pumping 
from  the  well.  The  outlet  is  1.5  feet  below  the  top  of  the  well,  which 
overflows  between  times  of  pumping. ' '  * 

302.  The   Third  Class  of  Springs,  which  are   mere   overflows  of 
ground-water  in  a  porous  formation,  are  to  be  treated  like  those  of  the 
second  class.      The  ground-water  streams  of  which  they  are  the  indi- 
cations   may  frequently  be    drawn    upon    to    advantage    by  wells    or 
galleries  arranged  with  little  reference  to  the  springs  themselves. 

THE    HYDRAULICS   OF    WELLS. 

303.  Before  entering  upon  a  discussion  of  the  various  forms  of  wells 
it  will  be  desirable  to  consider  the  hydraulic  principles  governing  the 
flow    of   water    into    them   from   the    surrounding    porous   formations. 
There  are  two  general  cases  to  be  considered:   (i)  Flow  into  ordinary 
wells,  where  the  upper  surface  of  the  ground- water  is  exposed  to  at- 

* Jour.  New  Eng.   W.  W.  Assn.,  1896,  XI.  p.  156. 


278 


WORKS   FOR    THE   COLLECTION  OF  GROUND-WATER. 


mospheric  pressure  through  the  porous  ground  above.  (2)  Flow  into 
artesian  wells,  where  an  impervious  layer  covers  the  porous  one,  thus 
enabling  the  water  to  flow  under  a  pressure  greater  or  less  than  the 
atmosphere.  General  formulas  relating  to  these  two  cases  will  be  dis- 
cussed separately,  after  which  matters  common  to  both  will  be 
considered. 

A.    Principles  Governing  the  Flow  into  Ordinary  Wells  and  Galleries. 

304.  General  Form  of  Ground-water  Surface.  —  If  a  well,  sunk  into 
a  body  of  ground-water,  be  drawn  from,  the  level  of  the  water  in  the 
well  will  be  lowered,  and  the  surface  of  the  ground-water  adjacent  to 
the  well  will  assume  a  form  similar  to- that  shown  in  Fig.  50.  In  this, 


Ground  L  eve  I 


FIG.  50.  —  SECTION  THROUGH  WELL. 

AB  is  the  original  surface  and  CDEF  the  new  surface.  The  amount 
which  the  surface  is  lowered  decreases  rapidly  as  we  get  farther  from 
the  well,  until  at  some  point  more  or  less  remote  there  is  no  sensible 
effect.  The  area  within  which  the  level  is  appreciably  lowered  is  called 
the  circle  of  influence. 

If  the  ground-water  is  present  merely  as  a  pond  or  reservoir  and 
the  pumpage  exceeds  the  percolation  on  the  area,  the  circle  of  influence 
will  gradually  enlarge  until  it  includes  the  entire  area  of  the  pond,  and 
the  water  will  in  time  be  exhausted.  If  there  is,  however,  a  general 
flow  of  the  ground-water,  a  well  will  be  lowered  only  until  the  circle 
of  influence  has  broadened  out  far  enough  to  cause  to  be  tributary  to 
the  well  an  area  into  which  the  flow  of  water  is  equal  to  the  pumpage. 

305.  Derivation  of  Formula  for  Flow. — In  Fig.  50  let  it  be  assumed 
that  AB,  the  original  surface  of  the  ground-water,  is  horizontal  and  at 
a  uniform  distance  H  above  an  impervious  stratum ;  that  the  porous 
material  is  uniform ;  and  that  the  well  is  sunk  to  the  impervious  stratum. 


THE   HYDRAULICS   OF   WELLS.  2/9 

Let  r  =  radius  of  well,  h  =  depth  of  water  in  the  well  when  in  opera- 
tion, H  =  original  depth  of  ground-water,  x  and  y  =  co-ordinates  of 
any  point  of  the  curve  CF  referred  to  the  bottom  of  the  well  as  origin, 
and  Q  =  rate  of  flow  into  the  well,  or  the  yield. 

The  total  available  head,  as  represented  by  H—h,  is  consumed  in 
four  ways  :  first,  and  mainly,  by  the  resistance  to  flow  in  the  ground  ; 
second,  by  the  entrance  resistance  into  the  well-tube  or  well  ;  third, 
by  friction  in  the  well-tube  in  ascending  to  DE\  and  fourth,  by  the 
head  necessary  to  give  the  rising  water  its  velocity.  For  shallow  wells 
all  but  the  first  are  usually  very  small,  and  for  the  present  they  will  be 
neglected.  Their  effects  in  exceptional  cases  are  noted  farther  on. 

The  equation  of  the  curve  CD  —  EF  will  now  be  derived.  The  flow 
being  radial,  the  area  of  the  cross-section  through  which  the  water 
passes  at  the  rate  Q  at  any  distance  x  from  the  center  is  that  of  a 
cylindrical  surface  equal  to  2  irxy.  In  Chapter  VII,  Arts.  85  and  88, 
it  was  shown  that  Q  in  cubic  feet  per  day  =  ksAp,  where  k  =  a  con- 
stant for  the  particular  sand  in  question  (see  Table  No.  20,  Art.  85), 
s  =  slope,  A  —  area  of  cross-section  in  square  feet,  and/  =  porosity. 

In  this  case  A  =  2  irxy  and  s  =  ~-t  whence 

dx 


Writing  this  in  the  form  Q  —  =2  irkpydy,  and  integrating,  we  have 


(i). 


.     .     .     ...     .    (2) 

in  which  \ogex  is  the  natural  or  hyperbolic  logarithm  of  x. 

When  x  =  r,   y  =  h,  whence  we   find  C  =  Q  \oger—Trkj>h2,  and 
substituting  and  solving  for  y2  we  have 


which  is  the  equation  sought.    The  units  are  the  foot  and  day. 

This  formula  assumes  the  water  to  flow  towards  the  well  from  an 
indefinite  distance,  and  the  curve  therefore  continues  to  rise  indefi- 
nitely, but  more  and  more  slowly  as  we  recede  from  the  well.  In  the 
actual  case  the  circle  of  influence  is  limited  on  account  of  the  flow  of 
the  body  of  ground-water,  this  flow  being  maintained  by  percolation 
either  near  or  remote.  Furthermore,  on  account  of  the  slope  of  the 
ground-water  surface,  the  curve  will  be  modified,  being  steeper  on  the 
up-stream  and  flatter  on  the  down-stream  side.  It  will  also  be  more 


280 


WORKS  FOR    THE    COLLECTION  OF  GROUND-WATER, 


or  less  irregular  on  account  of  variations  in  the  porosity  of  the  ground. 
But  the  general  form  of  the  curve  as  determined  by  actual  measurements 
agrees  quite  closely  with  the  theoretical  curve,  and  valuable  general  con- 
clusions may  be  drawn  from  a  theoretical  consideration  of  the  subject. 

If  in  equation  (3)  R  be  that  value  of  x  for  which  the  change  in 
water-level  is  inappreciable,  equal  to  the  radius  of  the  circle  of  influ- 
ence, the  corresponding  value  of  y  will  be  //",  the  original  depth  of 
water,  and  we  have 

' 


and  solving,  we  get  for  Q  in  cubic  feet  per  day 
H2  -  h2       -rrkt       H2 


or  in  gallons  per  day, 


R 
r 


in  which 


irkp  X  7-5 
2.30 

V  = 


H' 


h? 


log  — 

irkp  X  7-5 
2.30 


lo£7 


(4) 


(5) 


a  constant  depending  upon  the  fineness  and  the  porosity  of  the  material. 
All  distances  should  be  expressed  in  feet. 

306.  Calculation  of  Flow.  —  In  Table  No.  52  are  given  values  of  kf 
for  various  values  of  porosity  and  size  of  sand-grain.     Table  No.   53 

contains  values  of  the  quantity  -  —  of  equation   (5)  ;   they  are   also 


the  value  of  Q  for  kf  =  I  and  for  H2  —  h2  =  I .  To  find  Q  for  any  given 
value  of  k'  and  of  H2  —  k2  multiply  the  quantities  in  the  table  by 
k'  X  (H2  -  h2). 


TABLE    NO.  52. 

VALUES   OF    k'   IN   THE   FORMULA   Q=  k' 


-  h* 


i         - 

logr 


(d)    Effective  Size  of  Sand  in   Millimeters. 

Porosity 

Porosity 

Per  cent. 

Per  cent. 

.  10 

.20 

•30 

.40 

•  50 

.80 

I.  00 

2.00 

3-00 

25 

71 

286 

643 

1,140 

1,785 

4,56° 

7,140 

28,600 

64,250 

3C 

3° 

132 

525 

1,180 

2,090 

3,27° 

8,380 

13,200 

52,5°° 

117,900 

3° 

35 

218 

870 

i»955 

3.47° 

5,43° 

13,900 

21,840 

87,000 

i95>5°° 

35 

40 

336 

i»345 

3>°25 

5.38° 

8,400 

33,600 

134,5°° 

302,600 

40 

THE   HYDRAULICS   OF   WELLS. 


28l 


TABLE    NO.  53. 

VALUES   OF     / -  \      IN     EQUATION     (5) 


Diameter  of  Well. 


Feet. 

2  in. 

4  in. 

6  in. 

8  in. 

12  in. 

2  ft. 

4  ft. 

10  ft. 

20  ft. 

40  ft. 

100 

•325 

.360 

•384 

•403 

•435 

.500 

.588 

.770 

I.  000 

1.430 

200 

.296 

•325 

•344 

.360 

.384 

•435 

.500 

.625 

.770 

I.OOO 

500 

.265 

.287 

•3°3 

•3*5 

•333 

•37° 

.416 

.500 

.588 

•  715 

1000 

•245 

•265 

.278 

.287 

•3°3 

•333 

•37° 

•435 

.500 

.588 

2000 

.228 

•245 

.256 

.265 

.278 

•303 

•333 

•3»5 

•435 

.500 

500O 

.209 

.223 

•233 

•239 

.250 

.270 

.294 

•333 

•37° 

.417 

1  0000 

.197 

.209 

.217 

•  223 

•233 

.250 

.270 

•3°3 

•333 

•37° 

The  formula  or  tables  will  enable  approximate  values  of  Q  to  be 
determined  if  all  the  other  quantities  are  known.  With  shallow 
deposits  no  great  difficulty  arises  in  estimating  rough  values  for  k',  p, 
and  H\  h  is  determined  by  the  conditions  under  which  the  well  is  to 
be  operated,  and  r  is  the  known  radius  of  the  well, 

307.  The  Value  of  R.  —  In  none  of  the  above  quantities  is  there 
anything  that  involves  the  amount  of  water  actually  flowing  in  the 
ground,  and  it  is  obvious  that  without  some  knowledge  of  this  no 
formula  will  enable  one  to  predict  the  yield  of  a  well.  The  effect  of 
this  element  is  all  included  in  the  value  of  R,  the  radius  of  the  circle 
of  influence,  and  it  is  in  the  determination  of  this  that  the  chief  difficulty 
arises;  but  it  will  be  noted  from  Table  No.  53  that  large  variations  in 
R  affect  Q  but  little,  so  that  a  rough  approximation  will  be  sufficient. 
This  can  be  obtained  by  properly  conducted  tests  as  explained  in  Art. 
316,  or  it  can  be  estimated  as  follows  :  Assuming  that  all  the  water  in 
the  circle  of  influence  flows  into  the  well,  the  width  of  the  strip  of  the 
ground-water  stream  tributary  to  the  well  will  be  2  R,  and  the  original 
cross-section  of  this  portion  of  the  ground-water  stream  is  2  RH.  Then, 
as  on  page  279,  the  quantity  Q  =  ks  x  2  RH  X  /,  whence 


R=2JSWP-       •       •       •       •       '       '    •*      '       '        <6) 

By  substituting  the  value  of  Q  from  equation  (4)  we  have,  after  reduc- 
tion, 


7-7-1  -* 

2sHloge- 


282  WORKS  FOR    THE   COLLECTION  OF  GROUND-WATER. 

or,  as  H  —  h  is  usually  small  compared  to  Hy  we  have  approximately 


s  lo&  7 


s  Iog10- 


(8) 


from  which,  knowing  the  slope  s  and  the  depression  of  the  water-level 
(If  =  h),  R  cah  be  estimated  with  sufficient  accuracy  by  a  few  trials. 

It  is  to  be  noted  that  R  varies  inversely  with  the  slope,  and  from 
eq.  (5)  it  is  seen  that  Q  increases  as  R  decreases  ;  hence  for  a  given 
value  of  (H2  —  tf),  Q  will  be  greater  the  greater  the  slope,  and  with 
zero  slope  Q  will  be  zero.  This  is  an  important  point  ;  it  expresses 
mathematically  what  has  been  stated  in  Chapter  VII,  that  there  must 
be  an  actual  flow  of  the  ground-water  as  shown  by  an  hydraulic  slope 
in  order  that  any  definite  quantity  can  be  withdrawn  for  an  indefinite 
length  of  time. 

Table  No.  54  gives  values  of  R  from  eq.  (8)  for  various  values  of  r 


A    c 
and  of 


VALUES   OF    R  IN  FORMULA  R  —  1.36 


TABLE   NO.   54. 
H-h 


log  - 


H-h 

FOR  VARIOUS  VALUES  OF  AND  OF  T. 

S 


H-h 


Diameter  of  Well  (  =2r). 


s 

6  Inches. 

i  Foot. 

2  Feet. 

4  Feet. 

10  Feet. 

20  Feet. 

2OO 

104 

115 

129 

I46 

I76 

207 

4OO 

189 

208 

230 

258 

3°5 

352 

600 

269 

2QS 

325 

362 

423 

485 

800 

347 

378 

415 

461 

536 

610 

1,000 

422 

459 

503 

556 

645 

73° 

2,000 

779 

843 

919 

1010 

1150 

1290 

4,OOO 

1450 

1560 

1690 

1840 

2080 

2300 

6,000 

2080 

2240 

2410 

2620 

2950 

325° 

8,000 

2700 

2890 

3120 

337° 

3780 

415° 

10,000 

3280 

353° 

3800 

4110 

459° 

5030 

Considering  the  values  given  in  this  table  and  the  relatively  slight 
effect  of  a  large  variation  in  R,  shown  by  Table  53,  it  will  be  suffi- 
ciently accurate  in  most  cases  to  take  an  arbitrary  value  of  R  such  as 
1000.  In  the  nature  of  the  case  the  results  of  such  calculations  must  be 
looked  upon  as  only  crude  approximations  which  serve,  however,  as  a 
general  guide  and  as  a  check  upon  unreasonable  estimates. 


THE  HYDRAULICS   OF   WELLS.  283 

308.  Example.  —  To  apply  these  tables  to  an  example  let   it  be 
required  to  estimate  the  yield  of  a  6-inch  well  sunk  into  a  ground-water 
stream  30  feet  thick,  the  water-bearing  stratum  consisting  of  a  coarse 
sand  of  an  effective  size  of  0.4  millimeters  and  a  porosity  of  35  per 
cent.     Further,  suppose  the  slope  s  =••  20  feet  per  mile  =  .0038,  and 
that  the  water  is  to  be  drawn  down  5  feet  below  its  original  level.    Then 

H-  h  =  5,    h  =  25,  H~h  =  1320,    and    H2  -  /i2  =  275.      From 

TT   _     A 

Table  No.  54  we  find  for  —  ^—  =  1320,  R  =  about  500  feet.     From 

Table  No.  52  we  find  for  d  =  0.4  and/  =35  per  cent,  k'  =  3500. 

Finally,  by  the  aid  of  Table  No.  53,  we  find  a  value  of  Q  equal 
to  0.30  X  3500  X  275  =  290,000  gallons  per  day.  If  R  had  been 
taken  at  1000  the  result  would  have  been  270,000  gallons  per  day. 

309.  Effect  on  the  Yield  of  a  Change  in  the  Various  Elements.  —  The 
value  of  Q  from  eq.   (5)  is  seen  to  vary  directly  with  kf)  a  constant 
which  varies  directly  with  the  square  of  the  diameter  of  sand-grains  and 

with  the  porosity  of  the  material.     Furthermore,  Q  varies  inversely  as 

E> 
log  ->  and  the  values  given  in  Table  No.    53  show  that  Q  changes 

slowly  with  changes  in  the  values  of  either  R  or  r.  Thus,  other  things 
being  equal,  a  2-foot  well  will  yield  but  15  to  30  per  cent  more  than  a 
3-inch  well. 

Eq.  (5)  may  be  written  in  the  form 


.  . 

log- 


or  if  H  and  h  are  nearly  equal,  as  is  usually  the  case,  we  may  write 
approximately 

,tH(H-h) 

g=2/p_J  --  ^!,      .......       (I0 

i        -K 

log- 

from  which  it  is  seen  that  Q  is  directly  proportional  to  H  and  also  to 
H  —  ht  that  is,  to  the  depth  of  ground-water  and  to  the  depression  of 
the  water-surface.  Thus  if  in  pumping  at  the  rate  of  100,000  gallons 
per  day  from  a  well  the  water-surtace  is  depressed  2  feet,  approximately 
200,000  gallons  may  be  obtained  by  lowering  the  surface  4  feet.  If 
the  lowering  is  too  great,  then  eq.  (10)  becomes  more  in  error  and  Q 
will  increase  less  rapidly  than  the  value  of  H  —  h.  This  general 


284 


WORKS  FOR    THE    COLLECTION  OF  GROUND-WATER. 


relation  that  Q  varies  with  H  —  h  has  been  shown  to  be  very  nearly 
correct  in  many  cases  by  actual  tests  and  is  an  important  principle  to 
keep  in  mind. 

The  variation  in  yield  with  the  depression  of  water  level  is  graphi- 
cally shown  in  Fig.  5oa.     For  a  considerable  amount  of  lowering  the 


.20          .40          .60  .80        WO 

Proportionate  Lowering  of  Water  Level*  ^  - 

FIG.  5oa.  —  RELATION  OF  YIELD  TO  LOWERING  OF  WATER  LEVEL  IN  WELL. 

curve  is  nearly  straight,  but  as  the  level  approaches  the  bottom  of  the 
stratum  (100  per  cent  lowering)  the  rate  of  increase  is  small.  A  lower- 
ing of  50  per  cent  will  thus  give  a  yield  equal  to  75  per  cent  of  the 
yield  for  a  lowering  of  100  per  cent. 

3opa.  Flow  into  a  Gallery  or  a  line  of  Wells  Closely  Spaced. — 
Fig.  5ob  is  a  section  through  a  gallery  and  represents  conditions  similar 
to  those  shown  in  Fig.  50.  The  water  is  supposed  to  flow  to  the  gal- 
lery from  both  directions  under  a  head  (H —  /i),  equal  to  the  amount 
the  water  is  lowered  below  the  original  level  of  the  ground-water  sur- 
face, which  level  is  still  maintained  at  a  distance  R  from  the  gallery. 
Applying  the  same  method  of  analysis  as  in  Art.  305,  the  cross-section 
A  of  the  ground- water  stream  at  any  distance  x  from  the  gallery  is  (con- 
sidering both  sides)  equal  to  2y  per  unit  length  of  gallery.  The  slope 


/  1  •'I  O  J 

before,  s  =  —-j- ,  whence,  as  in  eq.  (i),  the  yield  per  unit  length  is 


is,    as 

given  by  the  equation 


Integrating    as    before   we    have    Qx  =  kpy*  +  C,    and   we    find 
C  =  —  h*kp,  whence  we  have 


that 


THE  HYDRAULICS  OF  WELLS. 


285 


(12) 


as  the  equation  of  the  curve  CD. 
have 


Substituting  H  for  y  and  ^  for  x  we 


(13) 


In  this  case  the  flow  is  seen  to  vary  with  //"and  h  in  the  same  manner 
as  in  the  single  well.  The  variation  with  R  is,  however,  very  different, 
being  now  inversely  proportional  to  R. 

In  the  case  of  galleries  and  rows  of  wells  the  calculations  here  given 
are  of  little  value  in  estimating  the  total  yield  unless  the  area  occupied 

Ground  Level 


FIG.  5ob.  —  SECTION  THROUGH  GALLERY. 

by  such  wells  is  comparatively  small  so  that  the  water  enters  from  all 
sides,  as  in  the  case  of  supplies  of  great  capacity  as  compared  to  the 
draught.  Galleries,  and  to  a  less  extent,  wells,  are  usually  arranged  to 
intercept  as  much  of  the  ground-water  flow  as  possible  so  that  most  or 
all  will  enter  from  the  up-stream  side.  The  yield  is  then  eventually 
a  question  of  the  amount  of  ground-water  flowing  through  the  area  in 
question. 

B.    Principles  Governing  the  Flow  into  Artesian  Wells. 

310.  Where  the  water  flows  under  pressure  in  a  porous  stratum 
overlaid  by  an  impervious  one,  the  flow  into  a  well  is  not  accompanied 
by  a  change  of  level  in  the  surface  of  the  water,  but  the  curve  of  pres- 


286 


WORKS  FOR    THE   COLLECTION  OF  GROUND-WATER. 


sures    is   of  a  form   similar  to  the  water-surface  in  the  case  already 
treated. 

In  Fig.  5 1  the  thickness  of  the  porous  stratum  is  /,  the  original 


Ground  Level 


FIG.  51.  —  SECTION  THROUGH  ARTESIAN  WELL. 

pressure-line  is  AB  (below  or  above  the  surface),  and  the  pressure-line 
existing  on  pumping  from  the  well  is  CD-EF.  The  derivation  of  the 
equation  of  the  curve  of  pressures  is  similar  to  that  in  Art.  305,  except 
that  in  this  case  the  water  passes  through  an  area  of  constant  depth  / 
instead  of  a  variable  depth  y.  Making  this  change,  eq.  (i)  of  Art. 
305  becomes 


from  which  we  readily  get,  as  before, 


H  -  h 


(ii) 


(12) 


in  which  k'  =  the  same  constant  as  before,  given  in  Table  No.  52, 
/  =  thickness  of  porous  stratum,  H  —  original  pressure-head  at  the 
bottom  of  the  stratum,  h  —  head  at  bottom  of  well  when  flowing,  R  = 
radius  of  circle  of  influence,  and  r  =  radius  of  well. 

This  equation  differs  from  (5)  only  in  having  the  constant  2t  in 
place  of  (H -\-  h},  and  hence  the  laws  of  flow  are  very  nearly  the  same 
as  in  the  previous  case ;  that  is,  Q  varies  directly  with  k ',  also  with 
H  —  h  (the  lowering  of  the  water  in  the  well),  and  with  /,  and  in- 
versely with  log  R. 

Where  an  artesian  stratum  lies  near  the  surface  it  can  be  investi- 
gated with  respect  to  hydraulic  slope,  material,  and  depth  as  readily 
as  the  other  class  already  discussed,  and  estimates  of  flow  made  in  the 


THE  HYDRAULICS  OF  WELLS.  287 

same  way.    In  using  Table  No.  53,  2t(H —  h)  should  be  used  in  place 


In  the  case  of  deep  artesian  wells  /  is  sometimes  several  hundreds 
of  feet,  and  H  —  h  is  also  often  very  large.  On  the  other  hand  k'  is 
usually  small,  and  likewise  the  slope,  but  on  the  whole  the  values  of 
Q  will  usually  be  much  larger  than  for  shallow  wells. 

An  important  test  showing  the  variations  of  Q  with  H  —  h  was 
carried  out  by  Prof.  Marston  on  a  well  2215  feet  deep  at^the  Iowa 
Agricultural  College  in  which  the  lowering  of  the  water  was  very 
great.*  The  results  were: 

Lowering  of  Water-level.  Yield. 

1 20  feet 10.2  cubic  feet  per  minute 

162    " 13.7      "       "       "       " 

184    " 15.1      "       "       "       " 

238    " 18.8     "       "      "       " 

Using  the  value  of  10.2  as  a  basis,   exact  proportion  would  call  for 
yields  of  13.8,  15.7,  and  20.3  cubic  feet  respectively. 

C.    Considerations  of  General  Application. 

311.  Pipe  Friction  and  Other  Losses  of  Head. — The  resistances  to 
flow  that  have  not  been  considered  are  the  friction  of  entrance  into  the 
well-tube  or  well,  the  friction  in  the  tube  itself,  and  the  velocity-head. 

Inadequate  area  of  openings  into  the  well,  and  the  effects  of 
clogging  and  corrosion,  may  cause  the  loss  of  head  at  entrance  to  be  a 
very  considerable  proportion  of  the  total  head.  This  question  is  further 
discussed  in  connection  with  the  constructive  features.  The  velocity- 
head  is  usually  too  small  to  be  worth  considering.  It  is  easily  figured 

v* 

in  any  case  from  the  formula  h  =  — . 

2£- 

The  friction-head  in  wells  up  to  50  or  100  feet  in  depth  is  usually 
small,  but  in  deep  wells  of  small  diameter  it  is  often  a  very  large  item 
and  needs  to  be  carefully  considered.  If  the  well  is  cased  for  a  large 
portion  of  its  length,  the  friction  can  be  figured  on  the  basis  of  the  fric- 
tion in  wrought-iron  pipes.  Where  not  cased  the  friction  would  prob- 
ably be  greater,  the  amount  depending  on  the  roughness  of  the  walls. 
It  will  be  sufficiently  accurate  for  present  purposes  to  estimate  it  as  25 
per  cent  greater  than  that  for  smooth  pipes,  and  Table  No.  55  has  been 
computed  on  that  basis.  It  gives  the  frictional  head  for  wells  100  feet 
deep  of  various  diameters  and  under  various  rates  of  flow.  By  the  use 

*  Eng. Record,  1898,  xxxvil.  p.  387. 


288 


WORKS  FOR    THE   COLLECTION  OF  GROUND-WATER. 


of  this,  together  with  the  principle  that  the  loss  of  head  due  to  the 
resistance  in  the  ground  is  closely  proportional  to  the  flow,  we  may 
compute  the  total  head  required  to  cause  any  given  yield  from  a  well, 
if  we  know  the  yield  for  any  particular  head ;  or,  knowing  the  flow 
from  a  well,  we  can  compute  approximately  the  yield  of  wells  of  other 
sizes  sunk  to  the  same  formation. 

TABLE    NO.   55. 

LOSSES    OF    HEAD   IN   TUBULAR   WELLS    DUE   TO    FRICTION    IN    WELL-TUBE   OR   WELL. 


Frictional 
Head. 
Feet  per 
100  feet. 

Discharge  in  Gallons  per  Day. 

a-inch. 

3-inch. 

4-inch. 

6-inch. 

8-inch. 

lo-inch. 

12-inch. 

0-5 

13,000 

39,ooo 

84,000 

250,000 

550,000 

1,000,000 

1,600,000 

I 

19,000 

56,000 

120,000 

350,000 

830,000 

1,500,000 

2,400,000 

2 

28,OOO 

84,000 

l8o,000 

550,000 

I,2OO,OOO 

2,2OO,OOO 

3,600,000 

3 

35,000 

110,000 

230,000 

700,000 

I,5OO,OOO 

2,700,000 

4,600,000 

4 

42,OOO 

120,000 

27O,OOO 

830,000 

I,800,000 

3,2OO,OOO 

5,300,000 

5 

47,000 

140,000 

3IO,OOO 

940,000 

2,000,000 

3  700,000 

6,2OO,OOO 

6 

53,000 

160,000 

350,000 

I,OOO,OOO 

2,300,000 

4.200,000 

6,900,000 

8 

62,000 

190,000 

400,000 

I,2OO,OOO 

2,600,000 

4.700,000 

7,9OO,OOO 

10 

69,000 

210,000 

47O,OOO 

I,4OO,OOO 

3,000,000 

5,500,000 

9,OOO,OOO 

15 

90,000 

270,000 

590,000 

1,700,000 

3,800,000 

7,000,000 

12,000,000 

20 

100,000 

310,000 

690,000 

2,OOO,OOO 

4,600,000 

8,300,000 

30 

130,000 

400,000 

860,000 

2,600,000 

5.600,000 

10,000,000 

40 

150,000 

460,000 

1,000,000 

3,000,000 

7,000,000 

312.  Illustrative  Calculations. — i.  Suppose  a  well  6  inches  in  diameter  and 
500  feet  deep  yields  500,000  gallons  per  day,  with  a  total  head  of  15  feet. 
Let  it  be  required  to  find  the  head  necessary  for  a  discharge  of  1,000,000 
gallons  daily.  In  the  first  case  the  loss  of  head  by  friction  is,  from  the  table, 
about  9  feet,  and,  neglecting  other  losses,  the  head  consumed  in  the  strata 
is  therefore  6  feet.  To  discharge  i,  000,000  gallons  requires  about  1 2  feet  head 
in  the  ground  and  30  feet  in  pipe-friction  =  42  feet  total  required  head,  or 
an  added  head  of  27  feet  over  that  required  for  a  yield  of  500,000  gallons. 

2.  Suppose  a  6-inch  well  1000  feet  deep  yields  1,000,000  gallons  per  day 
under  a  total  head  of  100  feet.     What  will  be  the  yield  of  a  4-inch  well  under 
the  same  head  ? 

From  Table  No.  55  the  frictional  head  in  the  6-inch  well  is  about  60  feet, 
and,  neglecting  other  losses  of  head,  the  head  lost  in  ground  friction  is 
100  —  60  =:  40  feet.  For  other  volumes  it  will  be  assumed  that  the  head  lost 
in  ground-friction  is  proportional  to  the  volume.  The  problem  now  is  to 
determine  an  amount  Q  for  the  4-inch  well  such  that  the  total  loss,  pipe  fric- 
tion and  ground  friction,  shall  be  100  feet.  It  is  readily  solved  by  trial. 
Thus  for  various  values  of  Q  the  losses  of  head  are: 

Q.  Pipe  Friction.  Ground  Friction.  Total. 

470,000  ioo  19  119 

400,000  80  1 6  96 

Hence  for  a  total  head  of  ioo  feet  Q  will  be  about  420,000  gallons  per  day. 

3.  As  illustrating  the  effect  of  size  of  well  where  the  pressures  and  depths 
are  great,  values  of  Q  have  been  computed  for  various  sizes  of  wells  in  accord- 


THE  HYDRAULICS   OF   WELLS. 


289 


ance  with  the  data  of  example  2,  so  that  the  total  loss  of  head  is  about  100 
feet  in  each  case.  They  are  given  in  the  adjoining  table  together  with  the 
losses  of  head. 


Diameter 
of  Well. 

Q. 

Galls,  per  day. 
....         68  OOO 

Pipe  Frict: 
Feet. 

97 
90 
85 
60 

35 
18 

9 

of   small 

ion.      Ground  Friction. 
Feet 

3 
8 
16 
40 
64 

1     "    . 

•  •  .  .         2OO  OOO 

4" 

420  ooo 

6     "    , 

j  OOO  OOO 

8     "    

I0      "     

.  .  .         2  lOOjOOO 

84 
92 
diameter  and  with  hit 

it  is  seen 

that   for  wells 

From  this 

pressures  the  yield  is  principally  dependent  upon  the  pipe  friction,  but  that 
with  large  diameters  the  yield  depends  rather  upon  the  ground  friction  and  is 
little  affected  by  the  diameter. 

313.  Examples  of  Wells  Flowing  under  High  Heads — In  the  Dakota 
artesian  basin  the  pressures  run  up  to  300  feet  and  over,  thus  giving  rise  to 
high  velocities  and  large  losses  of  head  from  pipe  friction.  The  great  differ- 
ences in  yields  from  different-sized  wells  there  noted  are  largely  due  to  this 
fact.  Below  are  given  data  of  several  typical  wells  taken  from  the  United 
States  Geological  Survey  Report,  1895-6,  Part  II.  A  column  of  "  computed 
yields  "  has  been  added,  the  computations  having  all  been  made  on  the  basis 
of  the  flow  of  the  8-inch  wells  and  on  the  assumption  that  all  the  water  flows 
the  entire  length  of  the  well.  Only  roughly  approximate  results  could  of 
course  be  expected,  as  the  wells  are  distributed  over  a  large  area  and  the 
water-bearing  stratum  is  more  or  less  irregular;  and,  besides,  the  observed 
yield  is  doubtless  in  many  cases  from  very  rough  measurements.  The  reported 
yields  for  some  of  the  smaller  wells  would  be  impossible  under  the  given  head 
if  all  the  water  entered  at  or  near  the  bottom. 

TABLE   NO.  56. 

DATA   OF   ARTESIAN   WELLS    IN   THE    DAKOTA   BASIN. 


Yield. 

Diameter, 
Inches. 

Depth, 
Feet. 

Static 
Head, 
Feet. 

Observed 
Gals,  per  Min. 

Computed, 
Gals,  per  Min. 

I 

480 

142 

30 

16 

2     ' 

715 

303 

200 

100 

2| 

880 

262 

280 

1  80 

3 

689 

300 

425 

320 

3 

1315 

287 

350 

2IO 

4* 

840 

345 

I  OOO 

900 

4i 

902 

352 

670 

750 

6 

712 

276 

1500 

1700 

6 

897 

142 

1200 

1000 

6 

1350 

138 

500 

850 

8 

530 

198 

3292 

2600 

8 

1000 

345 

2000 

3200 

8-10 

640 

253 

4350 

4000 

314.  Effect  of  Depth  of  Well. — It  has  been  assumed  in  the  preceding 
discussion  that  the  well  penetrated  to  the  impervious  stratum.      If  it 


290 


WORKS  FOR    THE   COLLECTION  OF  GROUND-WATER. 


reaches  short  of  this,  there  will  evidently  be  increased  resistance  near 
the  well  for  like  quantities  of  water,  or  for  the  same  head  the  flow  will 
be  decreased.  This  added  resistance  due  to  decreased  cross-section 
occurs  only  in  the  immediate  vicinity  oH;he  well,  and  if  the  total  loss 
of  head  or  total  depression  is  great,  and  if  the  well  extends  half  or 
two-thirds  through  the  porous  stratum,  the  added  resistance  will  be 
but  a  small  proportion  of  the  total  and  the  consequent  effect  on  Q  will 
not  be  great.  It  often  happens  that  the  water-bearing  formation  is 
made  up  of  layers  of  different  degrees  of  porosity,  so  that  the  resistance 
to  flow  from  one  stratum  to  another  would  be  very  great.  In  this  case 
the  yield  would  be  very  largely  influenced  by  the  depth  of  the  well. 

315.  Mutual  Interference  of  a  Number  of  Wells — If  two  or  more 
wells  penetrating  to  the  same  stratum  are  placed  near  together  and 
simultaneously  operated,  the  total  yield  will  be  relatively  much  less 
than  the  yield  of  a  single  well  pumped  to  the  same  level.  This  mutual 
interference  of  wells  depends  in  amount  upon  the  size  and  spacing  of 
the  wells,  upon  the  radius  of  the  circle  of  influence  of  the  wells  when 
operated  singly,  and  upon  the  depth  to  which  the  water  is  lowered  by 
pumping.  Professor  Slichter  has  investigated  this  subject  theoretically,* 
and  some  examples  given  by  him  of  the  application  of  his  formulas  will 
be  instructive. 

Assuming  the  wells  in  question  to  be  6  inches  in  diameter,  that  the 
water  is  lowered  10  feet  by  pumping,  and  that  R  =  600  feet,  the 
mutual  interference  of  a  group  of  two  wells,  a  group  of  three  wells,  and 
of  a  large  number  of  wells  placed  in  one  row  are  as  given  in  the  fol- 
lowing table.  The  amount  of  the  interference  is  expressed  as  the  per- 
centage of  reduction  in  yield  per  well  below  that  of  a  single  well 
uninfluenced  by  others.  According  to  the  figures  given  in  the  table 

TABLE  NO.  57. 

MUTUAL   INTERFERENCE    OF  GROUPS    OF    SIX-INCH    WELLS, 

(Water  lowered  10  feet  by  pumping.     R  =  600  feet.) 


Two  Wells. 

Three  Wells. 

Large  Number  of  Wells  in  a 
Row. 

Distance  Apart 
of  Wells. 

Interference. 

Distance  Apart 
of  Wells. 

Interference. 

Distance  Apart 
of  Wells. 

Interference. 

Feet. 

Per  cent. 

Feet. 

Per  cent. 

Feet. 

Per  cent. 

5 

38 

5 

55 

IOO 

66 

10 

35 

10 

51 

200 

45 

IOO 

20 

IOO 

31 

400 

24 

200 

16 

2OO 

22 

600 

14 

400 

ii 

400 

12 

IOOO 

6 

1000 

6 

IOOO 

8 

Report  U.  S.  Geolog.  Survey,  1897-98,  p.  371 


THE  HYDRAULICS  OF  WELLS.  291 

two  wells  200  feet  apart  will  yield  84  X  2  —  168  per  cent  as  much  as 
a  single  well.  If  a  third  well  be  placed  between  these  two,  the  yield 
will  be  69  X  3  =  207  per  cent  as  much  as  the  single  well.  If  a  large 
number  of  wells  are  placed  I  oo  feet  apart,  the  yield  of  each  is  but  34 
per  cent  as  much  as  it  would  be  if  operated  alone. 

316.  Determination  of  Yield  by  Tests. — Where  it  can  be  done,  the 
best  way  to  determine  Q  is  by  actual  tests  conducted  for  a  sufficient 
length  of  time  to  bring  about  a  condition  of  equilibrium  in  the  flow, 
but  unless  this  condition  is  approximately  fulfilled  such  tests  are  apt  to 
be  very  deceptive.  With  a  flat  slope  to  the  ground-water  a  test  may 
be  carried  on  for  weeks  and  even  months,  and  the  circle  of  influence 
will  still  continue  to  widen,  resulting  in  a  gradually  decreasing  yield. 
It  may  thus  require  years  of  operation  to  bring  the  conditions  to  a  final 
state  of  equilibrium  except  as  affected  by  variations  in  the  percolation. 
The  steeper  the  slope  the  quicker  the  conditions  become  constant ;  and 
to  aid  in  judging  of  results  obtained  by  pumping  tests,  the  ground-water 
slope  should  be  determined  when  possible. 

In  conducting  tests  on  shallow  wells  it  is  desirable  to  observe  the 
variations  in  ground-water  level  at  different  distances  from  the  well. 
This  will  aid  in  determining  when  equilibrium  has  been  reached,  and 
will  also  enable  R  to  be  estimated  and  will  give  information  as  to  the 
proper  spacing  of  a  series  of  wells. 

The  value  of  Q  being  found  for  the  test  well,  the  effect  of  variation 
in  the  size  of  the  well  and  in  the  lowering  of  the  water-level  can  be 
determined  from  the  theoretical  considerations  already  discussed.  As 
a  valuable  check  on  results  of  tests,  the  yield  should,  where  possible, 
be  estimated  by  the  method  explained  in  the  preceding  articles. 

As  an  example  of  long-continued  lowering,  the  operation  of  the 
large  well  in  Prospect  Park,  Brooklyn,  may  be  cited.  The  water-level 
varied  as  follows: 

Q  Volume  Pumped          Elevation  of  Water- 

per  Day.  level  above  Tide. 

Gallons.  Feet. 

1869 o          14-55 

iS/0 300,000  H-IS 

1871 272,000  13-03 

1872.... , ...  437,000  10.56 

1873 288,000  11.29 

1874 333,000  10.70 

1875 , 294,000  9.83 

1876  235,000  9.83 

1877 252,000  9.21 

1878 249,000  8.80 

1879...., 260,000  8,85 


292  WORKS  FOR    THE   COLLECTION   OF  GROUND-WATER. 

The  actual  capacity  of  the  well  appears  thus  to  be  about  250,000 
gallons  per  day. 

317,  Wells  Sunk  into  Strata  in  which  the  Flow  takes  Place  through 
Fissures, — The  preceding  analysis  has  been  based  upon  the  assumption 
that  the  water  flows  through  the  interstices  of  the  porous  material.  In 
some  rock  formations,  however,  much  of  the  flow  undoubtedly  takes 
place  through  fissures.  This  is  apt  to  be  the  case  with  limestone 
strata,  the  passageways  in  this  material  sometimes  assuming  large 
dimensions,  due  to  the  solvent  action  of  the  water. 

The  effect  of  these  fissures  is  greatly  to  increase  the  capacity  of  the 
material  and  at  the  same  time  to  modify  the  law  of  flow.  The  resist- 
ance to  flow  through  large  fissures  will  vary  approximately  as  the 
square  of  the  velocity,  instead  of  as  the  first  pov/er ;  and  as  one  result 
the  yield  of  a  well  supplied  largely  in  this  way  will  not  increase  at  the 
same  rate  as  the  lowering  of  the  water  in  the  well,  but  much  more 
slowly.  As  a  matter  of  fact  most  wells  in  sandstones  do  follow 
approximately  the  law  of  the  proportionality  of  yield  and  head,  but  it 
has  been  observed  in  the  case  of  some  limestone  wells  that  there  is  a 
large  departure  from  it  in  the  direction  above  indicated. 


CONSTRUCTION   OF  WELLS. 

318,  Forms  of  Construction, — The  various  forms  and  sizes  of  wells 
used  to  collect  ground-water  may  be  divided  into  the  following  classes : 
(i)   Large  open  wells;   (2)  shallow  tubular  wells;  and  (3)  deep  and 
artesian  wells. 

No  sharp  line  of  division  can  be  said  to  exist  between  shallow  wells 
and  deep  wells,  and  in  many  matters  that  which  applies  to  one  class 
applies  equally  well  to  the  other.  It  will,  however,  be  convenient  to 
divide  them  into  the  above  classes,  the  methods  of  construction,  of 
investigation,  and  of  operation  being  in  many  respects  different  in  wells 
of  25  feet  to  100  feet  deep  than  in  wells  of  greater  depth.  One 
hundred  feet  may  be  roughly  taken  as  the  limit  of  shallow  wells. 

319.  Location   of   Wells. — To    procure   water    economically  in    the 
large  quantities  required  for  public  supplies,  it  was  made  evident  in  the 
discussion  on  the  flow  of  ground-water  that  there  must  be  present  a 
water-bearing  formation   of  considerable   extent    and   porosity.     The 
location  of  such  a  deposit  is  here  supposed  to  have  been  determined 
upon  through  borings  and  tests,   and    as    a  general  requirement    the 
works  for  collection  should  be  so  placed  as  to  intercept  for  a  given 
expense  as  large  a  quantity  of  water  as  possible. 


CONSTRUCTION  OF   WELLS.  293 

It  has  been  shown  that  the  more  the  water  in  a  well  is  lowered  the 
greater  is  the  yield.  A  favorable  location  for  a  well-plant  will  therefore 
usually  be  at  a  point  where  the  ground-water  is  reached  with  the  least 
lift  of  the  pumps.  This  will  ordinarily  be  on  low  ground  and  often  in 
the  vicinity  of  surface  streams.  If  wells  in  such  a  situation  are  pumped 
too  low,  they  will  draw  water  from  the  stream  as  well  as  from  the 
ground-water,  a  result  sometimes  undesirable.  In  some  cases  it  may 
be  allowable  to  obtain  filtered  surface-water  in  this  way,  but  this  use  of 
wells  will  be  discussed  subsequently.  For  the  present  it  will  be 
assumed  that  all  the  flow  is  strictly  ground-water. 

320.  Relative  Advantages  of  Large  and  Small  Wells, — The  yield  of 
any  form  of  well  is  a  question  rather  of  the  flow  of  the  ground-water 
and  of  the  area  made  tributary  by  the  depression  of  the  water-level  in 
a  well,  than  a  question  of  the  size  or  form  of  construction.  The 
discussion  in  Art.  309  shows  that  the  effect  of  size  alone  is  very  small, 
and  that  therefore  we  need  not  expect  an  increase  in  the  yield  of  large 
wells  commensurate  with  increase  in  size.  The  increase  in  flow  is, 
however,  something;  and  in  the  case  where  the  circle  of  influence  is 
small,  or  where  the  water  is  present  in  large  quantities,  the  increase 
may  be  very  considerable. 

The  large  well  possesses  a  great  advantage  over  the  small  well  in 
its  storage  capacity.  If  the  pumping  is  carried  on  at  a  variable  rate,  it 
thus  acts  to  increase  greatly  the  real  capacity  of  the  large  well  over 
that  of  a  series  of  small  tube-wells.  Furthermore,  in  the  operation  of 
the  pumps  there  are  many  advantages  in  being  able  to  get  the  entire 
supply  from  a  single  well,  or  from  two  or  three  large  wells  close 
together,  chief  among  which  is  the  avoidance  of  long  suction-pipes. 
The  large  well  is  also  of  great  advantage  where  it  becomes  necessary 
to  lower  the  pumps,  as  it  permits  the  use  of  a  more  economical  form 
of  pumping  machinery. 

Trouble  is  often  experienced  in  the  small  wells  through  clogging 
and  the  entrance  of  fine  sand.  This  is  largely  avoided  in  the  large 
well,  as  the  entrance  velocity  of  the  water  is  very  small.  Opportunity 
is  also  given  for  the  settling  of  fine  material. 

The  chief  disadvantage  of  the  large  well  is  in  its  great  cost  com- 
pared to  the  tube-well  for  like  yields.  This  disadvantage  increases 
rapidly  as  the  depth  increases,  and  where  it  may  be  economy  to  con- 
struct a  large  well  to  a  certain  depth  to  serve  as  a  pump-pit  it  will 
usually  be  cheaper  to  develop  the  yield  by  sinking  tube-wells  from  the 
bottom,  or  by  driving  galleries  therefrom,  than  by  further  sinking. 


294  WORKS  FOR    THE    COLLECTION  OF  GROUND-WATER. 

Except  where  used  as  pump-pits  it  will  seldom  be  economical  to  adopt 
the  large  well  for  depths  exceeding  30  or  40  feet. 

It  may  be  said,  therefore,  that  large  wells  are  suited  for  places  where 
the  water  can  be  reached  at  moderate  depths,  where  the  excavation  is 
not  difficult,  where  a  single  large  well  will  furnish  the  desired  amount, 
and  where  the  pumps  are  to  be  operated  but  a  few  hours  of  the  day. 
The  tubular  well  is  particularly  suited  for  developing  a  supply  from  a 
wide  area  and  from  strata  of  irregular  character,  and  for  penetrating 
deep  strata. 

Large  Open  Wells. 

321.  Size   and  Depth  of  Wells. — Large  wells   for  water- works  are 
constructed  of  diameters  of  10  feet  or  less  to  as  great  as  100  feet,  30  to 
50  feet  being  the  most  common  size.      The  best  size  must  be  deter- 
mined from  a  consideration  of  the  various  factors  mentioned  in  Art. 
320;  but  as  the  cost  of  a  well  increases  with  increase  in  diameter  more 
rapidly  than  does  the  yield,  a  very  large  diameter  should  be  adopted 
only  after  most  careful  consideration. 

322.  The   minimum  depth  of  a  well  is  determined  by  the  depth 
necessary  to  reach  and  penetrate  for  a  short  distance  the  water-bearing 
stratum,  allowing  a  margin  for  dry  seasons.      Beyond  this  it  should  be 
extended  to  allow  for  storage,  and  to  permit  of  such  a  lowering  of  the 
water-level  as  is  estimated  will  be  the  most  economical  with  the  form 
of  pump  employed,  or  such  as  will  be  necessary  to  secure  the  desired 
amount  of  water. 

323.  Construction. — In  the  first  place,  it  is  to  be  noted  that  large 
quantities  of  water  will  be  met  with,  and  if  the  excavation  is  to  be 
made  in  the  open,  adequate  means  of  handling  it  must  be  provided. 
As  the  water-level  must  be  kept  at  the  lowest  level  of  the  excavation, 
the   maximum   pumpage   will   be   considerably  more  than   the  future 
capacity  of  the  well.      For   moderate  depths  the   excavation   can  be 
carried  on  with  no  other  aid  than  sheet-piling.      If  the  well  is  of  large 
diameter,  an  annular  trench  is  usually  first  excavated  and  the  curb  or 
lining  built  therein,   after  which  the  interior  core  is  removed.     This 
method   enables   the   sheet-piling   to   be   readily   braced.      A   method 
adapted  to  smaller  wells  is  to  drive  the  sheet-piling  outside  of  a  series 
of  wooden  frames  or  ribs,   and  to  excavate  the  entire  well  at   once. 
The  ribs  are  built  in  place  as  the  excavation  proceeds.     This  method 
is  illustrated  in  Fig.  53,  page  296. 

For  wells  of  considerable  depth  sunk  in  soft  material,  the  curb  may 
be  started  on  a  shoe  of  iron  or  wood,  and  the  excavation  and  the  con- 


LARGE    OPEN    WELLS. 


295 


struction  of  the  curb  carried  on  simultaneously,  the  curb  sinking  from 
its  own  weight.  The  material  may  be  either  excavated  in  the  ordinary 
way,  or  by  the  use  of  compressed  air,  or  dredged  out  without  attempt- 
ing to  keep  out  the  water,  the  method  used  depending  upon  depth  of 
well,  quantity  of  water,  and  character  of  the  material.  Where  the  fric- 
tion becomes  too  great  to  sink  the  first  curb  the  desired  distance,  a 
second  curb  with  shoe  may  be  sunk  inside  the  former.  In  Fig.  52  are 
illustrated  two  forms  of  shoes  used  in  sinking  wells.  These  are  both 
constructed  mainly  of  wood.  To  strengthen  such  ciu'bs  iron  rods  should 


FIG.  52. — SHOES  FOR  SINKING  WELL-CURBS. 

extend  from  the  shoe  well  up  into  the  masonry.  For  large  wells,  pump- 
pits,  etc.,  heavy  iron  shoes  are  often  employed,  and  occasionally  a 
pneumatic  caisson  is  found  necessary. 

The  lining  or  curb  usually  consists  of  a  circular  wall  constructed  of 
concrete  or  masonry  of  a  thickness  varying  with  diameter  and  depth  of  the 
well,  and  the  material  employed.  If  concrete  is  used,  slightly  reinforced,  a 
thickness  of  12  to  18  inches  will  usually  be  ample.  The  upper  portion  of 
the  lining  should  be  impervious  in  order  to  prevent  the  entrance  of  imper- 
fectly filtered  surface  water.  If  the  well  is  to  be  fed  from  strata  that  are 
partly  or  wholly  cut  off  by  the  curbing,  entrance  for  the  water  should 
be  provided  for  by  laying  the  wall  dry  or  by  means  of  special  openings. 
The  entrance  of  fine  sand  through  such  openings  can  be  prevented  by 
a  back  filling  of  broken  stone  and  gravel  suitably  graded  in  fineness. 
A  lining  of  cast-iron  segments  bolted  together  has  been  frequently 
employed  in  sinking  deep  wells,  especially  in  Europe,  where  wells  of 
5  to  10  feet  in  diameter  and  75  to  100  feet  deep  are  quite  common. 

All  wells  should  be  covered  to  exclude  the  light  and  to  prevent 
pollution  of  the  water.  The  cover  is  usually  made  of  wood,  which  for 
large  wells  may  be  conveniently  made  of  a  conical  form  and  supported 
by  a  light  wooden  truss,  or  by  rafters  resting  against  the  wall. 


296 


WORKS  FOR    THE   COLLECTION  OF  GROUND-WATER. 


324.  Yield. — The  actual  yield  of  large  wells  which  are  considered 
successful  varies  from  100,000  to  4  or  5  million  gallons  per  day,  the 
higher  values  being  very  exceptional.  A  computation  of  the  carrying 
capacity  of  ordinary  porous  material  by  the  methods  explained  in  a 
preceding  chapter  will  show  that  for  a  single  well  to  furnish  one  million 
gallons  per  day  requires  a  very  extensive  tributary  area  and  a  con- 
siderable lowering  of  the  water-level  in  the  well. 


-3  Sectional  Plan  of  Well  under  Construction. 


Vertical  Section  of  Well  under  Construction. 


FIG.  53.— LARGE  WELL  AT  ADDISON,  N.  Y. 

(From  Engineering  Ne-ws^  vol.  xxxin.) 

325.  Examples. — At  Peoria,  111.,  a  well  36  feet  in  diameter  was  sunk  on 
a  wooden  shoe  with  cast-iron  cutting  edge  to  a  depth  of  44  feet  through  clay 
to  a  water-bearing  gravel.  During  sinking,  from  n  to  13  million  gallons  per 
day  were  pumped.  The  curb  is  a  3O-inch  brick  wall.* 


*  Eng.  News,  1892,  xxvm.  p.  26. 
Wells  "  at  end  of  chapter. 


See  also  Reference  No.  16  under  "Driven 


SHALLOW   TUBULAR    WELLS.  297 

At  Webster,  Mass.,  a  well  25  feet  in  diameter  was  sunk  in  gravel  to  a 
depth  of  30  feet,  sheet-piling  being  driven  on  the  outside  of  circular  ribs  made 
of  3-inch  plank  bolted  together.  Two  sets  of  piling  were  used.  The  curb 
was  built  as  a  dry  rubble  wall  5  feet  thick  at  base  and  2  feet  thick  at  top, 
with  a  12-inch  brick  lining  laid  in  cement.  Two  6-inch  centrifugal  pumps 
were  used  during  construction,  the  maximum  pumpage  being  i  million 
gallons  per  day.  The  cost  complete  was  $13, 190.* 

At  Addison,  N.  Y.,  an  auxiliary  supply  was  obtained  from  a  well  12.5 
feet  in  diameter  and  23  feet  deep.  Fig.  53  illustrates  clearly  the  method 
there  used  in  sinking.  On  account  of  very  soft  material  the  well  was  stopped 
short  of  the  necessary  depth  and  the  water-bearing  stratum  was  reached  by 
twenty-three  i£-inch  tubes  driven  from  7  to  20  feet  below  the  bottom  of  the 
well.  The  yield  was  165,000  gallons  per  day.  The  curb  is  a  2o-inch  wall 
in  cement,  and  the  cover  is  of  flagging  laid  on  I  beams.  The  cost  was,  for 
the  excavation  $2.18  per  cubic  yard,  and  for  the  masonry  $5.82.  The  total 
cost  was  $851. 

Shallow  Tubular  Wells. 

326.  Shallow  tubular  wells  or  wells  of  small  diameter,  also  called 
driven  wells, t  are  sunk  in  various  ways,  depending  upon  the  size  and 
depth  of  well  and  nature  of  the  material  encountered.     As  wells  for 
public  supplies  would  rarely  be  sunk  in  rock  except  to  a  considerable 
depth,  the  methods  of  construction  here  considered  will  refer  only  to 
shallow  wells  sunk  in  soft  material.     To  furnish  large   quantities   of 
water  it  usually  requires  a  number  of  wells,  and  in  addition  to  the 
question  of  sinking,    questions  of  arrangement,   spacing,   connecting, 
and  operation  are  important.      While  the  strata  penetrated  by  shallow 
wells  are  often  artesian  in  character,  yet  this  fact  is  of  little  consequence 
in  this  case,  as  the  pressures  would  be  small  and  the  method  of  con- 
struction  and  operation  the  same  as  for  wells  tapping  the  ordinary 
ground-water. 

327.  Methods  of  Sinking. — As  regards  methods  of  sinking  there  are 
two  principal  kinds  of  wells:  the  closed-end  well  or  driven  well  proper, 
and  the  open-end  well. 

328.  The  Closed-end  or  Driven  Well. — In  this  form  the  well-tube 
consists  of  a  wrought-iron  tube  from  I  to  4  inches  in  diameter,  closed  and 
pointed  at  one  end,  and  perforated  for  some  distance  therefrom.      The 
tube  thus  prepared  is  driven  into  the  ground  by  a  wooden  maul  or 
block  until  it  penetrates  the  water-bearing  stratum.      The  upper  end  is 
then   connected   to   a   pump  and  the  well    is   complete.     Where  the 

*  Jour.  New  Eng.   W.   W.  Assn.,  1895,  IX.  p.  240. 

f  The  term  "  driven  well  "  is  somewhat  loosely  applied  to  small  tubular  wells  of  all 
kinds  where  the  tube  is  sunk  largely  by  driving.  It  is  also  used  in  a  more  restricted 
sense  to  denote  a  closed-end  well  sunk  wholly  by  driving  and  without  the  removal 
of  any  material. 


290  WORKS  FOR    THE   COLLECTION   OF  GROUND- WATER. 

material  penetrated  is  sand  the  perforated  portion  is  covered  with  wire 
gauze  of  a  fineness  depending  upon  the  fineness  of  the  sand.  To  pre- 
vent injuring  the  gauze  and  clogging  the  perforations,  the  pointed  end 
is  usually  made  larger  than  the  tube,  or  the  gauze  may  be  covered  by 
a  perforated  jacket. 

Fig.  54  shows  a  common  form  of  well-point  and  a  method  of  driv- 
ing wells  by  means  of  a  weight  operated  by  two  men.     The  tube  may 


FIG.  54. — WELL-POINT  AND  DRIVING-RIG. 

also  be  driven  by  a  wooden  block  operated  by  a  pile-driver  or  other 
convenient  means. 

The  well  above  described  is  adapted  for  use  in  soft  ground  or  sand 
up  to  a  depth  of  about  75  feet,  and  in  places  where  the  water  is  thinly 
distributed.  On  account  of  the  ease  with  which  it  can  be  driven, 
pulled  up,  and  redriven,  it  is  useful  in  prospecting  at  shallow  depths, 
and  in  fact  groups  of  wells  are  often  finally  located  by  driving  and 
testing  until  a  good  result  is  obtained. 

329.  Open-end  Wells. — For  use  in  hard  ground  and  for  the  larger 
sizes  the  open-end  tube  is  better  adapted.  This  is  sunk  by  removing 
the  material  from  the  interior,  and  at  the  same  time  driving  the  tube 
as  in  the  other  case.  A  very  common  method  of  sinking  is  by  means 
of  the  water-jet.  In  this  process  a  strong  stream  of  water  is  forced 
through  a  small  pipe  inserted  in  the  well-tube,  the  water  escaping  in 
one  or  more  jets  near  the  end  of  the  pipe.  At  the  same  time  the  pipe, 
which  is  provided  with  a  chisel  edge,  is  churned  up  and  down  to 
loosen  the  material,  which  is  then  carried  to  the  surface  by  the  water 
in  the  annular  space  between  the  pipe  and  tube.  If  the  material  is 
hard  or  the  well  deep,  a  steel  cutting-edge  may  be  screwed  on  to  the 
end  of  the  well-tube. 

Fig.  55  shows  an  outfit  used  by  Mr.  L.  L.  Tribus,  Mem.  Am.  Soc. 


SHALLOW  TUBULAR    WELLS. 


299 


C.  E.,  in  jetting  down  6-inch  wells  at  Pensacola,  Fla  to  a  depth  of 
90  to  130  feet.* 

The  driving  was  done  by  a  hammer  weighing  1000  pounds  and 
operated  by  a  pile-driver.  The  jet-pipe  was  worked  under  a  water- 
pressure  of  75  pounds  and  churned  up  and  down  by  a  rope  led  over 
the  head  of  the  pile-driver  and  wound  on  another  spool  of  the  pile- 
driver  engine.  One  engineman,  one  driller,  and  two  laborers  operated 
the  machine,  and  with  this  force  6-inch  pipes  were  driven  140  feet  in 
ten  hours.  Similar  methods  have  been  used  in  several  recent  investiga- 
tions of  ground-water  supplies  and  in  the  construction  of  permanent 
plants.  In  the  extensive  investigation  made  on  Long  Island  by  the 
New  York  Water  Supply  Commission  a  2OO-pound  hammer  was  used, 
operated  by  ropes  running  through  blocks  attached  to  a  pipe  derrick. 
The  average  cost  per  foot  of  two-inch  test  wells  was  about  $i.oo.f 

A  process  similar  to  the  water-jet  has  been  used  in  which  steam  is 
employed  instead  of  water.  Another  method  is  to  remove  the  material 
by  means  of  a  sand-bucket.  \ 

Extra-strong   pipe,    called    drive-pipe,    is    ordinarily    used    for   well 


FIG.  55.— JETTING  APPARATUS.  FIG.  56. — COOK  WELL-STRAINER. 

« 

tubes,  care  being  taken  that  the  joints  are  screwed  up  so  that  the  ends 
of  the  pipe  are  in  contact. 

*  Eng.  Record,  1898,  xxxvn.  p.  428. 

t  Report  of  Commission,  1903,  p.  629.     Various  driving  rigs  are  illustrated. 

t  See  also  stove-pipe  method  in  Art.  345. 


300  WORKS  FOR    THE    COLLECTION  OF  GROUND-WATER. 

330.  Strainers.  —  With  the  open-end  well  the  lower  portion  may  be 
merely  perforated  with  small  holes  in  case  the  material  is  coarse  or 
gravelly,  or  if  sand  is  met  with  the  holes  may  be  covered  with  brass 
gauze.  Instead,  however,  of  using  a  gauze  it  is  common  with  this 
style  of  well  to  sink  a  solid  tube,  insert  a  special  strainer  of  suitable 
length,  and  then  withdraw  the  tube  nearly  to  the  top  of  the  strainer. 
If  necessary  a  tight  joint  can  then  be  made  between  the  tube  and 
strainer  by  means  of  a  short  piece  of  tubing  or  lead  packer  cut  to  a 
bevel. 

Fig.  56  illustrates  a  commonly  used  form  of  strainer  known  as  the 
Cook  strainer.  It  is  made  of  brass  tubing  and  provided  with  very 
narrow,  slotted  holes,  which  are  much  wider  on  the  interior  than  on 
the  exterior,  an  arrangement  intended  to  prevent 
clogging.  Fig.  56a  illustrates  the  Johnson  strainer, 
a  very  ingenious  and  satisfactory  form.  It  is  made 
up  of  a  strip  of  brass  of  special  section,  spirally 
wound  upon  a  temporary  core.  Successive  turns  of 
the  sjrip  interlock,  thus  forming  a  continuous  cylin- 
der of  any  desired  length  and  diameter.  Between 
successive  strips  a  narrow  slit  of  any  desired  width  is 
formed  on  the  outside,  through  which  the  water  may 
pass  into  an  interior  annular  space  and  thence  through 
large  circular  holes  into  the  well.  The  width  of 
outer  slot  is  made  from  .004  to  .02  inch.* 

Strainers  of  the  type  just  described  are  intended 
TOHNSON^TRAINER  to    Prevent    tnc    mnow  °^    sand    and  are  especially 
(From  Engineering  News,  use^ u*  where  the  water  bearing  material  contains  little 
VOL.LV.)  or  no  coarse  material.     The  resistance  to  entrance 

immediately  adjacent  to  the  slots  will  be  relatively  great  as  the  water  is 
forced  to  pass  through  a  very  small  sectional  area.  This  results  in  a 
considerable  loss  of  head  unless  the  size  and  length  of  strainers  are 
carefully  proportioned  to  the  requirements.  Where  coarse  material  is 
present  with  the  fine,  a  coarse  strainer  or  perforated  pipe  may  be  used 
to  advantage.  This  will  permit  the  inflow  of  some  fine  material,  but  as 
this  escapes  the  coarser  particles  will  form  a  natural  strainer  outside  the 
pipe  of  much  greater  effective  cross- section.  Before  the  wells  are 
placed  into  service  the  fine  sand  should  be  removed  by  rapid  pumping, 
or  by  the  sand  buckets,  or  it  may  be  loosened  and  washed  out  by  a  jet- 
ting bit.  This  general  result  may  also  be  accomplished  in  the  case  of 

*  Eng.  News,  1906,  LV.  p.  260. 


SHALLOW  TUBULAR    WELLS. 


301 


fine  sand  by  inserting  a  coarse  strainer  of  smaller  diameter  than  that  of 
the  well,  filling  between  strainer  and  well  tube  with  coarse  sand  cr 
gravel  and  then  drawing  up  the  tube.  A  very  large  gravel  strainer  has 
been  successfully  used  by  Mr.  D.  H.  Maury  at  Peoria.*  This  general 
-scheme  is  used  in  the  form  of  well  illustrated  in  Fig.  57.  In  this  the 
strainer  is  made  of  perforated  vitrified  pipe.f  This  type  of  well  has 
been  used  successfully  in  the  Brooklyn 
plant,  the  strainers  being  4  or  8  inches  in 
diameter  and  the  outer  casings  12  or  18 
inches  respectively.  In  very  fine  material 
two  or  three  layers  of  sand  of  graded  size 
can  be  used  so  as  to  effectually  prevent 
clogging  and  filling  of  the  well.  A  re- 
movable basket-strainer  has  also  been  used 
with  success. 

In  some  waters  strainers  have  given 
trouble  by  corroding,  thus  necessitating  re- 
moval and  cleaning.  Small  perforations 
in  ordinary  pipe  are  also  apt  to  give  trouble 
by  rusting.  This  has  been  avoided  in 
some  cases  by  bushing  the  holes  with  brass 
and  in  other  waters  galvanized  pipe  is  more 
successful,  the  holes  being  drilled  and 
reamed  before  galvanizing. 

The  length  of  the  strainer  or  perforated 
portion,  in  order  to  reduce  the  friction  in 
the  ground  to  a  minimum,  should  be  equal 
to  the  thickness  of  the  porous  stratum 
passed  through,  but  the  resistance  to  flow  FIG.  57. —THE  DOLLARD  WELL. 
will  be  but  slightly  increased  if  it  is  made 

materially  shorter,  even  half  or  one-third  the  thickness.  The  total 
area  of  the  perforations  should  be  sufficiently  large  to  keep  the 
velocity  of  entrance  down  to  2  or  3  inches  per  second,  both  to  keep 
the  friction  loss  low  and  to  prevent  the  entrance  of  sand.  Some- 
times open-ended  tubes  without  perforations  are  employed,  and  in  the 
case  of  thin  strata  the  yield  may  be  nearly  as  great  as  with  perfo- 
rated tubes.  With  thick  strata,  however,  the  resistance  to  entrance 
would  be  greatly  increased  if  all  the  water  is  forced  to  enter  at  the 
bottom. 


•  G  nor  re/  ancf  3am/ 


*  Eng.  News,  1904,  LIT.  p.  138. 
t  Ibid.  1896,  xxv.  p.  114. 


-302          WORKS  FOR    THE    COLLECTION   OF   GROUND-WATER. 

332,  General  Method  of  Operating  a  Well  System, — Small  tubular 
wells  are  usually  arranged  in  one  or  two  rows  alongside  a  suction-pipe 
and  connected  thereto  by  short  branches.      The  smaller  sizes  are  con- 
nected directly  to  the  branch,  the  well  -tube  acting  also  as  a  suction- 
pipe,   but  with  the  larger  sizes  a  separate   suction-pipe    is  ordinarily 
employed.      In   the   former   case,   to  avoid   the   entrance  of  air,   it  is 
necessary  that  the  perforated  portion  of  the  pipe  be  always  under  water, 
and  to  insure  this  being  the  case  it  should  be  kept  below  the  limit  of 
suction.     With  the  latter  arrangement  there  are  no  such  limitations  to 
the  position  of  the  perforated  well-casing. 

Since  the  amount  of  water  that  can  be  pumped  from  a  given  system 
of  wells  increases  with  the  amount  that  the  water-level  is  lowered  (up 
to  the  point  where  the  water-level  is  reduced  to  the  bottom  of  the 
water-bearing  stratum),  and  as  this  is  limited  by  the  limit  of  suction,  it 
is  always  desirable  to  make  the  connection  between  wells  and  pumps 
at  least  as  low  as  the  pumps.  In  many  cases,  to  increase  the  yield 
the  suction-pipe  is  laid  at  a  considerable  depth  in  the  ground,  and  the 
pumps  are  lowered  accordingly.  This  of  course  increases  the 
expense  of  construction,  and  as  the  height  to  which  the  water  is 
pumped  is  increased,  it  also  adds  to  the  cost  of  operation.  The 
most  economical  design  can  be  arrived  at  only  by  a  due  consideration 
of  all  these  elements. 

The  effect  of  an  extreme  amount  of  lowering  is  apt  to  be  a  some- 
what serious  matter  in  causing  the  drying  up  of  wells  and  springs  and 
even  of  streams,  and  recent  court  decisions  indicate  that  a  city  cannot 
draw  too  greatly  upon  the  ground-water  without  rendering  itself  liable , 

333,  Arrangement  and   Spacing  of   Wells.  —  The    most   favorable 
arrangement  for  a  system  of  small  wells  is  in  a  line  at  right  angles  to 
the  direction  of  flow  of  the   ground-water,  as  in  this  way  the   largest 
possible  area  will  be  drawn  upon.     By  placing  the  wells  across  the  line 
of  flow  or  along  a  ground-water  contour,  the  advantage  of  equal  heads 
in  the  several  wells  is  also  secured.      Where  but  a  small  area  or  width 
needs  to  be  drawn  upon,  the  arrangement  is  not  so  material,  as  the 
water  will  flow  towards  the  wells  from  all  directions ;  but  with  a  long 
line  of  wells  and  a  large  draft  it  becomes  a  question  of  much  impor- 
tance.    The  amount  of  water  which  can  be  obtained  from  a  system  of 
wells  depends  upon  the  average  amount  which  the  water-level  can  be 
lowered  along  the  line  of  wells.      The  ground-water  surface  through  a 
line  of  wells  when  in  operation  will  have  some  such  form  as  shown  in 
Fig.  58,  A,  B,  C,  and  D  being  the  wells,  L  M  the  original  level  of 
ground-water,  and  NOP  QR,  etc.,  the  new  surface.     The  yield  will 


SHALLOW   TUBULAR    WELLS. 


303 


be  some  function  of  the  average  lowering  h.  If  intermediate  wells, 
E,  Ft  and  G,  are  inserted  and  pumped  to  the  same  level  as  the  others, 
the  surface  will  be  N  O'  P,  etc.,  the  average  lowering  now  being  /?, 


FIG.  58. — SECTION  THROUGH  LINE  OF  WELLS. 

and  more  water  will  be  extracted  with  the  same  amount  of  suction ; 
but  if  the  circles  of  influence  of  the  first  wells  already  intersect,  the 
additional  amount  drawn  from  the  intermediate  wells  will  be  much  less 
than  the  yield  from  the  others. 

The  maximum  amount  of  water  obtainable  from  a  given  number  of 
wells  would  be  when  they  are  spaced  far  enough  apart  so  that  their 
circles  of  influence  will  not  overlap,  but  on  account  of  cost  of  piping, 
and  loss  of  head  by  friction,  this  .would  not  be  the  most  economical 
spacing.  If  wells  are  deep  and  therefore  expensive,  they  should  be 
spaced  to  interfere  comparatively  little;  if  shallow,  then  closer.  As 
indicating  what  the  mutual  interference  of  wells  may  be,  the  examples 
given  on  page  290  are  of  some  value.  In  practice  the  extent  of  this 
interference  can  best  be  judged  by  pumping  tests  of  trial  wells  or  of 
those  first  sunk,  the  wells  being  operated  at  different  rates  and  in 
various  combinations.  The  information  thus  obtained,  together  with  a 
knowledge  of  items  of  cost,  will  enable  the  best  spacing  of  subsequent 
wells  to  be  determined. 

While  it  is  impossible  to  give  figures  which  would  be  of  general 
application,  it  may  be  stated  that  from  25  to  100  feet  is  about  the  range 
for  economical  spacing  of  shallow  wells.  With  very  deep  or  artesian 
wells  the  spacing  becomes  still  greater.  Spacing  less  than  25  feet  has 
quite  often  been  used,  but  with  doubtful  economy. 

The  principles  here  discussed  relating  to  arrangement  and  spacing 
have  frequently  been  overlooked  in  the  location  of  small  wells,  and 
many  instances  exist  where  they  have  been  placed  in  such  a  way  that 
a  small  part  of  the  actual  number  would  furnish  as  much  as  the  entire 
group.  In  one  case  seventeen  3 -inch  and  6-inch  wells  were  placed  in 
an  area  within  a  circle  125  feet  in  diameter,  and  a  pump  test  showed 
that  seven  would  furnish  as  much  water  as  the  entire  seventeen.  In 
another  case  six  4-inch  wells  were  placed  in  a  row  10  feet  apart,  and 
a  test  showed  one  well  to  furnish  half  as  much  as  the  six.  In  still 


304  WORKS  FOR    THE    COLLECTION  OF  GROUND-WATER. 

another  case  twenty-four  2 -inch  wells  were  placed  in  an  area  20  feet 
by  95  feet.  Wells  so  placed  that  they  do  not  extend  the  general  circle 
of  influence  do  not  add  to  the  flow. 

334.  Size  of  Well.— It  has  been  shown  (Art.  309)  that  the  effect 
upon  the  yield  of  a  considerable  change  in  size  of  well  is  very  small 
provided  that  the  head  lost  by  friction  in  the  well-tube  is  small.      A 
well  should  therefore    be  large  enough  to  keep  the  friction  loss  within 
low   limits,    but    beyond    this    little    advantage    is   gained    by  further 
increase.      The  proper  size  thus  depends  upon  the  quantity  obtainable 
per  well,  and  this  in  turn  upon  the  spacing.     The  size  and  spacing 
should  therefore  be  considered  together.     With  the  shallow  wells  under 
consideration  the  slight  additional  cost  of  the  larger  well  will  make  it 
economical  to  keep  the  friction-head  down  to  a  few  inches  or  at  most 
I  or  2  feet,  corresponding  to  velocities  not  exceeding  2  or  3  feet  per 
second.      A   low    friction-head,    besides    making    the    pumping    more 
economical,  also  increases  the  suction  limit  of  the  pump  and  hence  the 
capacity  of  a  given  number  of  wells.      For  estimating  frictional  losses 
for  different  sizes  of  wells,  use  may  be  made  of  Table  No.  55,  page 
288. 

In  many  cases  the  best  size  and  spacing  are  largely  influenced  by 
the  means  available  for  sinking  the  wells. 

335.  As  illustrating  the  relation  between  size  and  spacing,  reference  may 
be  made  to  the  various  plants  of  the  Brooklyn  Water-works.*     Some  of  the 
driven-well  plants  of  these  works  yield  20,000  to  40,000  gallons  per  day  per 
well  from  2-inch  wells  about  50  feet  deep  and  spaced  about  13  feet  apart  in 
two  rows.     If  a  much  wider  spacing  were  adopted  and  a  larger  quantity  per 
well  expected,  it  would  manifestly  be  necessary  to  use  at  least  a  3 -inch  well, 
or  else  a  great  loss  of  head  would  result.    Another  plant  yields  about  200,000 
gallons  per  well  from    6-inch  wells  (4^-inch    suction-pipes)  spaced  40   feet 
apart,  a  yield  which  would  be  impossible  from  2-inch  wells.     To  procure  the 
same  yield  from  2-inch  wells  with  the  same  friction -head  would  require  about 
seven  times  as  many  wells,  but  with  a  closer  spacing  a  less  lowering  of  water 
in  the  well  would  be  required,  so  that  for  the  same  total  loss  of  head  perhaps 
five  times  as  many  wells  spaced  8  feet  apart  would  "be  equivalent.     This  would 
probably  be  a  more  expensive  arrangement  than  that  with  the  larger  wells. 
A  still  more  economical  arrangement  than  the  one  used  might  be  to  space  the 
wells  say  100  feet  apart,  using  6-inch  suctions  and  8-inch  wells. 

336.  Details  of  Connections. — Each  well  should  be  connected  to  the 
suction-main  by  means  of  a  short  branch  in  which  should  be  placed  a 
gate-valve,  so  that  any  well  can  be  shut  off  at  any  time.     Where  the 
well-tube  itself  is  connected  to  the  main  it  has  been  found  convenient 
to  insert  a  short  piece  of  lead  pipe  to  allow  of  easy  adjustment,  as  the 

*  Brooklyn  Water-supply,  Department  of  City  Works,  1896. 


SHALLOW  TUBULAK    WELLS.  305 

well  is  likely  to  be  slightly  out  of  plumb.  Connection  should  be  made 
at  the  well  by  means  of  a  curved  T,  from  the  vertical  branch  of  which 
the  well-tube  should  extend  to  the  surface  and  there  be  capped.  This 
arrangement  makes  the  well  readily  accessible  for  inspection  and 
cleaning  purposes.  To  reduce  friction  as  much  as  possible,  the  con- 
nection of  branch  to  main  may  be  made  with  a  Y  branch  instead  of 
a  T.  The  main  suction-pipe  is  usually  made  of  flanged  pipe,  as  this 
enables  air-tight  joints  to  be  more  readily  made,  although  ordinary 
bell-and-spigot  pipe  with  lead  joints  has  been  successfully  used. 

The  greatest  care  must  be  taken  in  every  part  to  make  the  work 
air-tight,  and  to  secure  this  it  should  be  thoroughly  tested  in  sections 
by  means  of  compressed  air.  All  valves  should  be  carefully  tested  for 
air-tightness,  and  all  screw  connections  thoroughly  fitted.  Mr.  Free- 
man C.  Coffin  in  certain  specifications  *  prescribes  that  the  suction- 
main,  and  branches  up  to  the  valves,  shall  be  tested  by  air  at  a 
pressure  of  50  pounds  per  square  inch,  which  pressure  once  secured 
shall  be  maintained  without  pumping.  The  valves  are  tested  under 
100  pounds  pressure. 

If  settling  of  main  is  feared,  special  foundations  must  be  provided. 
Main  and  branches  are  usually  laid  underground,  both  for  protection 
and  to  increase  the  range  of  pump-suction.  The  pipe  system  should 
be  made  of  sufficient  size,  and  all  connections  so  designed  as  to  reduce 
the  friction  to  the  lowest  limits  consistent  with  economy.  This  will 
require  the  use  of  velocities  not  exceeding  I  or  2  feet  per  second. 
The  suction-main  should  be  laid  on  a  slightly  ascending  grade  toward 
the  pump  to  prevent  lodgment  of  air  at  any  point.  All  perforations  in 
suction-pipe,  or  in  well-tube  used  as  such,  should  be  below  the  limit 
of  suction. 

337.  Air-separator. — In  spite  of  the  most  careful  construction,  air 
will  usually  accumulate  to  some  extent,  and  to  eliminate  it  many  plants 
are  provided  with  air- separators  placed  on  the  suction-main  near  the 
pump.     The  simplest  form  consists  of  a  large  drum  of  wrought  iron 
through  which  the  water  passes  at  a  slow  velocity  and  in  a  thin  sheet, 
either  over  broad  horizontal  surfaces  or  over  several  weirs,  in  order  to 
promote  the  escape  of  air.     To  this  drum  a  vacuum-pump  is  attached, 
which  in  some  cases  is  arranged  to  work  automatically.      Some  plants 
are  successfully  operated  without  a  separator. 

338.  Sand-box. — Where  sand  is  drawn  up  with  the  water  it  may 
be  got  rid  of  by  passing  the  water  at  a  slow  velocity  through  a  large 

*  Quoted  in  Goodell's  Water-works  for  Small  Cities  and  Towns,  p.  119. 


306  WORKS  FOR    THE    COLLECTION  OF  GROUND-WATER. 

drum  or  box  inserted  in  the  suction-pipe  and  provided  with  suitable 
hand-holes  for  cleaning. 

339.  The  Clogging  of  Wells  by  filling-  with  sand  or  by  corrosion  of 
the  screen  is  a  frequent  occurrence  and  may  reduce    the  yield  very 
greatly.      Wells  may  be  readily  cleaned  of  sand  by  means  of  the  sand- 
pump  or  bucket,  but  if  the  strainers  are  corroded  they  must  be  pulled 
up,  cleaned  or  renewed,  and  replaced.      If  the  clogging  is  due  to  fine 
sand  collecting  about  the  outside  of  tube,  it  may  be  removed  to  some 
extent  by  forcing  water  into  the  wells  under  high  pressure,*  or  by  the 
use  of  a  hose,  or  by  means  of  a  steam-jet.      Sometimes  instead  of  the 
yield  of  a  well  becoming  less  through  continued  operation  it  is  actually 
increased,  owing  probably  to  the  gradual  removal  of  the  finer  material 
immediately  surrounding  the  well.    ' 

340.  Tests. — Besides  the  preliminary  tests  already  mentioned  for 
determining  the  character  of  the  strata,   slope,  and  flow  of  ground- 
water,  spacing  of  wells,  etc.,   a  tube-well  system  should  always  on 
completion  be  subjected  to  a  thorough  test  as  to  capacity.      Such  tests 
should  be  continued  until  the  ground-water  level  has  reached  a  state 
of  equilibrium  as  determined  by  careful  observations  at  the  wells  and 
at  various  distances  therefrom.      If  possible  the  tests  should  extend 
over  the  dry  months  of  the   year,  and  where  the  system  is  built  by 
contract  to  supply  a  certain  amount  of  water,  the  successful  operation 
of  the  works  for  a  year  under  a  definite  head  should  be  a  prerequisite 
to  final  acceptance.      If  the  quantity  pumped  is  large  in   proportion  to 
the  capacity  of  the  ground,  a  long  time  will  elapse  before  the  ground- 
water  will  cease  to  fall.      The  case  mentioned  on  page  291  is  instruc- 
tive in  this  connection. 

341.  Yield. — The  maximum  possible  yield  of  a  ground-water  source 
would  be  when  the  entire  flow  is  utilized.      With  a  system  of  wells  this 
can  be  accomplished  only  in  case  the  water  can  be  drawn  to  the  bottom 
of  the  porous  stratum,  or  can  be  drawn  so  low  that  there  is  no  head  to 
cause  flow  away  from  the  wells   on  the  lower  side.      If  the  wells  are 
located  near  a  body  of  water  and  the  level  of  the  water  in  the  wells  is  kept 
as  low  as  that  of  the  surface-water,  the  entire  flow  will  then  be  utilized. 
In  special  cases  an  artificial  dam  can  be  constructed  and  a  line  of  wells  or 
a  gallery  placed  above,  as  at  Daggett,   Cal.     (Art.    357).     Ordinarily, 
however,  only  a  part  of  the  flow  is  intercepted,  the  proportion  depending 
upon  the  actual  lowering  compared  to  the  maximum  as  above  explained. 

The  actual  yield  in  any  case  will  depend,  of  course,  upon  the  condi- 
tions relative  to  the  ground-water  ;  but  where  these  conditions  have 
*  This  method  is  regularly  employed  at  Memphis.     See  Eng.  Record,  1902,  XLVI. 
P-  $13- 


SHALLOW   TUBULAR    WELLS. 


307 


been  favorable,  as  at  Brooklyn,  yields  of  300,000  to  500,000  gallons 
per  day  per  100  feet  of  suction-main  are  common.*  At  Plainfield  the 
yield  is  about  250,000  gallons  per  100  feet.  Conditions  are  often  less 
favorable  than  at  these  places,  and  yields  are  likely  to  be  much  less; 
but  if  the  ground-water  is  distributed  so  thinly  that  the  yield  would  be 
but  20,000  to  30,000  gallons  per  day  per  100  feet,  the  cost  of  suction- 
main,  wells,  land,  etc.,  would  render  a  ground-water  project  very 
expensive.  It  would,  however,  be  rarely  possible  in  such  a  case  to 
find  water-bearing  strata  sufficient  in  extent  to  furnish  any  except  very 
small  supplies. 

342.  Examples. — The   tubular-well  system   at  Plainfield,    N.   J.,   is  an 
example  of  a  very  successful  plant  (Fig.  59).     It  consists  of  twenty  6-inch 


Plan 

FIG.  59. — TUBULAR  WELLS  AT  PLAINFIELD,  N.  J. 

wells  of  perforated  pipe,  open  at  the  lower  end  and  provided  with  separate 
4^-mch  suction-pipe?.  The  wells  are  from  35  to  50  feet  deep,  and  are  sunk 
into  a  coarse  water-bearing  gravel  overlaid  by  clay.  They  are  spaced  about 
50  feet  apart  and  are  connected  to  the  suction-main  by  5-inch  branches. 
The  suction-main  varies  in  size  from  8  to  12  inches.  The  ground-water  at 
this  place  has  a  slope  of  about  3  feet  in  1900,  indicating  a  copious  flow. 
A  24-hour  pumping-test  indicated  a  yield  of  about  150,000  gallons  per  day 
per  well  with  ten  wells  connected,  and  a  depression  of  water-level  of  only 

*  The  estimated  underflow  of  Long  Island  is  at  least   10  in.  per  year  or  475,000 
als.  per  day  per  sq.  mi.  of  watershed. 


308  WORKS  FOR    THE   COLLECTION  OF  GROUND-WATER. 

2  feet.  At  700  feet  distant  the  lowering  in  a  test  well  was  0.6  foot.  With 
more  wells  operated  the  yield  per  well  was  less.  From  Table  No.  55,  page 
288,  it  is  seen  that  the  size  of  the  well  is  none  too  great  for  the  yield.  Fig. 
59  shows  the  arrangement  of  wells  and  details  of  well  and  manhole.  The 
cap  of  the  well  is  tapped  for  a  vacuum-gauge  connection.* 

A  very  economically  constructed  system  is  that  at  Brookline,  Mass.  The 
wells,  of  which  there  are  160,  are  2\  inches  in  diameter  and  from  35  to  95 
feet  deep.  They  are  open  at  the  bottom  and  perforated  for  the  lower  2  feet, 
the  holes  being  bushed  with  f  inch  brass  pipe.  They  are  arranged  along  a 
suction-main  about  6000  feet  long.  Each  well  is  connected  to  this  main  by 
means  of  two  short  pieces  of  lead  pipe  between  which  is  placed  a  gate-valve. 
The  cost  of  driving  and  connecting  up  118  good  wells  averaging  50  feet  deep, 
including  work  done  in  driving  and  pulling  up  41  unsuccessful  wells,  was 
147.90  per  well.  The  average  rate  of  driving  with  four  men  was  50  feet  per 
day,  at  a  cost  of  21  cents  per  foot  for  labor,  f 

The  city  of  Brooklyn,  N.  Y.,  obtains  a  large  proportion  of  its  water- 
supply  from  small  wells.  In  1895,  of  the  total  supply  of  about  75  million 
gallons,  about  35  million  was  from  wells,  and  an  additional  well -supply  of  25 
million  gallons  was  contracted  for.  The  old  wells  are  nearly  all  of  the  small 
closed  type  and  are  grouped  at  six  stations.  Fig.  60  shows  a  plan  of  one  of 


E/igtne  a/xf  &o/, 


I1IIIIII1IIIIIIIIII1II  V  IIIIMIIIIIIIIIIIIIIIIIIIIIIIIII1 

<  "  66      " 


FIG.  60. — FOREST-STREAM  DRIVEN-WELL  STATION,  BROOKLYN,  N.  Y. 

these  older  stations.  J  The  arrangement  is  quite  similar  in  all,  the  wells 
being  placed  in  two  rows,  one  on  each  side  of  the  suction-main.  The  later 
plants  are  to  consist  of  open  wells  perforated  and  covered  with  screens,  with 
suction-pipes  placed  inside.  A  description  of  one  of  the  new  plants  is  as  fol- 
lows: The  main  suctions  are  about  2340  feet  long  with  a  fall  of  12  inches 
from  centre  to  each  end.  The  62  wells  are  staggered  along  the  main  suction- 
pipe,  12  feet  from  it  and  75  feet  apart  on  each  side.  Their  average  depth  is 
45  feet,  a  stratum  of  fine  sharp  sand  being  met  with  at  that  depth.  The 
outside  casing  is  4-J-  inches,  with  6-foot  strainer,  2-foot  sand-pocket,  and 
6-inch  point.  Suctions  are  3  inches  in  diameter  and  28  feet  long.  Lateral 
branches  are  3^  inches,  and  each  is  provided  with  a  gate.  It  is  expected  to 
get  6  million  gallons  from  this  station.  The  contract  price  for  the  last  25 
millions  was  $167,250  for  sinking  and  connecting  wells,  the  yield  to  be 
determined  by  a  test  lasting  one  year  and  taken  as  the  lowest  average  for  five 
consecutive  days.§ 

*  Trans.  Am.  Soc.  C.  E.,  1894,  xxxi.  p.  371. 
t  Jour.  New  Eng.  W.  W.  Assn.,  1897,  xi.  p.  196. 
J  Brooklyn  Water-supply,  Plate  25. 

§  See  Report  of  Commission  on  Additional  Water-supply  of  New  York,  1903,  for 
further  data. 


DEEP  AND   ARTESIAN   WELLS.  309 

Deep  and  Artesian  Wells. 

343.  Comparison  with  Shallow  Wells. — Where  the  depth  exceeds 
75  to   100  feet  the  small  driven  well  is  no  longer  practicable.     The 
expense  of  construction   per  well  now  becomes  much  greater,  prelimi- 
nary investigation   much   more  difficult,   and  the  problem  altogether 
requires  more  careful  consideration.     Fortunately  the  deeper  strata  are 
usually  more  uniform  and  of  greater  extent  than  strata  near  the  surface, 
so  that  in  regions  already  explored  deep  wells  can  be  sunk  with  far 
more  certainty  of  success  than  is  usually  the  case  with  shallow  wells. 
Methods  of  sinking  deep  wells  are  in  many  respects  different  from  those 
already  described,  and  matters  of  spacing,   pipe-friction,  arrangement 
of  connections,  etc.,  are  much  more  important  than  in  the  shallow- 
well  plant. 

344.  Boring  Deep  Wells. — Well-boring  is  an  art  by  itself,  and  the 
execution  of  any  deep-well  project  should  usually  be  put  into  the  hands 
of  some  reliable  well-drilling  concern.      The  variety  of  ingenious  tools 
and  appliances  in  use  for  overcoming  all  kinds  of  difficulties  and  for 
penetrating  all  sorts  of  strata  is  very  great,  and  it  is  possible  to  give 
here  but  a  very  general  description  of  some  of  the  methods  of  sinking 
in  use.     The  methods  used  for  soft  and  for  hard  materials  are  very 
different,  and  the  subject  will  be  divided  accordingly. 

345.  Sinking  of  Wells  in  Soft  Materials. — In  soft  material  it  is  of 
course  necessary  to  case  the  well  the  entire  depth,  and  on  account  of 
the  difficulty  of  getting  the  casing  down  to  great  depths  this  operation 
becomes  the  chief  feature  of  the  construction. 

For  depths  up  to  200  or  300  feet  the  ordinary  well-drilling  outfit 
can  be  used,  and  the  casing  driven  close  after  the  drill.  By  the  use  of 
an  expansive  drill  the  hole  can  be  made  slightly  larger  than  the 
casing,  thus  making  it  possible  to  drive  the  casing  much  farther,  and 
even  enabling  strata  of  soft  rock  to  be  passed.  When  the  casing  can 
be  driven  no  farther  a  smaller  size  is  inserted  and  the  sinking  continued 
with  a  smaller  drill,  and  so  on  until  the  well  is  sunk  as  far  as  desirable 
or  possible.  The  material  excavated  is  brought  to  the  surface  by 
means  of  a  sand-bucket,  or  by  the  water-jet  as  previously  described 
in  Art.  329,  the  water  being  conducted  to  the  end  of  the  drill  through 
hollow  drill-rods.  By  the  latter  method  the  hole  is  kept  clean  and  a 
more  rapid  progress  made. 

The  friction  against  the  casing  is  greatly  lessened,  and  the  depth 
attainable  much  increased  by  the  use  of  the  revolving  process.  In  this 
the  lower  end  of  the  casing  is  provided  with  a  toothed  cutting-shoe  of 


310  WORKS  FOR    THE   COLLECTION  OF  GROUND-WATER. 

hard  steel  of  slightly  greater  diameter  than  the  pipe,  and  the  upper  end 
is  connected  by  means  of  a  swivel  to  a  water-pipe  through  which  water 
is  forced  by  suitable  pumps.  The  well  is  bored  by  turning  the  pipe, 
and  the  loosened  material  is  carried  to  the  surface  by  the  water  which 
passes  down  inside  the  casing  and  up  on  the  outside  between  casing 
and  soil.  So  long  as  the  water-pressure  is  maintained  there  is  very 
little  friction  between  the  earth  and  the  pipe,  and  the  tube  is  readily 
rotated  and  sunk  at  the  same  time.  This  process  is  very  common  in 
sinking  artesian  wells  in  the  alluvial  basins  of  California.  It  is  very 
rapid,  a  rate  of  sinking  as  high  as  20  or  30  feet  per  hour  for  depths  of 
1000  feet  having  been  attained. 

It  is  essential  to  have  a  good  length  of  strainer  in  the  porous 
stratum.  This  is  usually  inserted  after  the  desired  depth  has  been 
reached,  and  the  casing  is  then  pulled  up  to  the  top  of  the  strainer. 
By  special  devices  it  can,  however,  be  attached  to  the  end  of  the  well- 
casing  and  sunk  with  it. 

A  very  efficient  method  of  well-sinking  in  deposits  of  sand  and 
gravel  is  that  so  largely  employed  in  Southern  California  and  known 
as  the  "  stove-pipe  "  method  of  construction.  Wells  of  this  type  are  put 
down  in  gravel  and  boulder  deposits  or  other  unconsolidated  material 
to  depths  as  great  as  1300  feet.  The  usual  size  ranges  from  8  to  14 
inches.  After  the  first  length  the  casing  consists  of  short  sections, 
two  feet  long,  of  No.  12  riveted  sheet  steel.  It  is  of  double  thickness, 
and  is  made  up  as  the  well  is  sunk  by  telescoping  the  sections  together 
using  alternately  an  "  inside"  and  an  " outside  "  section,  breaking  joints 
at  the  center  of  each  section.  The  pipe  is  thus  smooth  both  inside 
and  outside. 

The  material  from  the  inside  is  usually  removed  by  a  large  sand 
bucket  operated  with  jars,  and  the  casing  is  forced  down  by  heavy 
hydraulic  jacks.  After  the  well  is  sunk  the  casing  is  slotted  by  special 
perforating  knives  which  operate  very  effectively.  The  cost  of  such 
wells  is  remarkably  low,  a  5oo-foot  well  costing  in  1903  about  $700, 
not  including  the  casing. 

The  chief  advantages  of  this  type  of  well  consist  in  its  strength  of 
joint,  smoothness,  convenience  of  construction,  and  low  cost.  The  large 
size  is  also  very  advantageous  where  boulders  are  encountered,  and 
where  large  yields  are  met  with.* 

346.  Examples.  —  At  Memphis,  8-inch  wells  were  sunk  by  the  jetting  pro- 
cess. A  lo-inch  well  was  first  sunk  70  to  90  feet  to  clay,  to  cut  off  undesirable 

*  Eng.  Newsy  1903,  L.  p.  428. 


DEEP  AND   ARTESIAN   WELLS.  311 

water,  and  the  8-inch  pipe  was  then  forced  down  by  means  of  an  hydraulic 
jack  anchored  to  the  ic-inch  pipe."  In  this  way  a  depth  of  600  feet  could  be 
reached.  In  one  case  a  6-inch  pipe  was  continued  inside  the  8-inch  to  a  total 
depth  of  1165  feet.  Cook  strainers  50  feet  long  were  used,  J  inch  smaller 
than  the  8-inch  casing,  and  closed  at  the  bottom.  After  being  lowered  the 
casing  was  pulled  up  nearly  to  the  top  of  the  strainer,  and  a  ring  packing  of 
rubber  and  brass  driven  between  strainer  and  tube.* 

A  very  deep  well  was  sunk  by  the  revolving  process  at  Galveston,  Texas. 
The  first  casing  was  22  inches  in  diameter  and  was  sunk  57  feet.  This  was 
followed  by  1 5-inch  casing  to  a  depth  of  870  feet;  then,  following  this,  pipes 
of  i2-inch,  9  inch,  8-inch,  7-inch,  6-inch,  and  5-inch  diameter  were  used, 
with  which  a  depth  of  3067  feet  was  reached.  The  contract  price  was  $75,000 
for  a  depth  of  3000  feet.  The  cost  of  the  plant  ready  for  work  was  $12,000. 
A  water-pressure  of  250  pounds  per  square  inch  was  used  in  sinking. t 

347.  Boring  Wells  in  Rock.  — A  drilling  outfit  for  deep  wells  is  very 
similar  to  the  ordinary  familiar  outfit  for  shallow  wells  worked  by 
horse-power.  A  string  of  tools  consists  essentially  of  a  steel  bit,  an 
auger-stem  into  which  the  bit  is  screwed,  a  pair  of  links  or  "jars" 
connecting  the  auger-stem  with  another  bar,  called  a  sinker-bar,  and 
finally  the  rope  cable  which  supports  the  apparatus  and  which  passes 
over  a  pulley  at  the  top  of  a  derrick  and  then  down  to  a  winding 
drum.  Just  above  the  drum  the  cable  is  attached,  by  means  of  an 
adjusting  or  "temper"  screw,  to  a  large  walking-beam  operated  by  a 
steam-engine.  As  the  work  progresses  the  drill  is  lowered  by  the 
temper-screw.  By  means  of  the  jars  an  upward  blow  may  be  struck 
to  dislodge  a  jammed  drill.  Many  ingenious  tools  are  employed  for 
recovering  lost  tools,  cutting  up  and  removing  pipe,  and  carrying  on 
the  various  operations  involved. 

Wooden  poles  are  sometimes  employed  to  support 
this  system  is  not  much  used  in  the  United 
States.  Its  advantage  lies  in  the  greater 
command  the  driller  has  over  the  drill,  both 
in  turning  it  and  in  maintaining  a  straight 
hole.  Its  chief  disadvantage  is  in  the  length 
of  time  required  to  remove  the  drill  from  the 
hole. 

In  this  country    deep    wells  are  almost      ^^ 
invariably  of   small    diameter.     In    Europe,  FIG-  61.— LARGE  WELL-BORING 
however,  deep-bore  wells  are  frequently  con- 
structed of  a  diameter  of  2  to  4  feet  and  even  as  large  as  6  feet.     One 
such  well  is  the  Place  Herbert  well  of  Paris,  3j  feet  in  diameter  and 

*   Eng.  Record,    1891,  xxiv.  p.  234. 
t   Eng.  News,  1892,  xxvin.  p.  122. 


312  WORKS  FOR    THE    COLLECTION   OF  GROUND-WATER. 

2536  feet  deep.*  At  Southampton,  England,  two  6-foot  wells  spaced 
n^  feet  apart  were  bored  in  chalk  to  a  depth  of  100  feet.  They  were 
intended  to  serve  also  as  pump-pits.  The  boring  apparatus  used  at 
this  place  is  illustrated  in  Fig.  6i.f 

As  already  shown  in  Art.  309  the  effect  of  size  of  well  upon  the 
yield  is  not  great,  so  that  in  this  respect  large,  deep  wells  are  of  doubt- 
ful economy.  It  may,  however,  often  be  economical  to  build  a  well 
large  enough  to  serve  as  a  pump-pit,  thus  permitting  the  use  of  a  more 
economical  type  of  pump  than  would  otherwise  be  possible.  (See  also 
Art.  352.) 

348.  Casing  of  Wells.  —  Wells  in  soft  material  must  be  cased 
throughout.  When  bored  in  rock  it  is  necessary  to  case  the  well  at 
least  through  the  soft  upper  strata  to  prevent  caving.  Casing  is  also 
desirable  for  the  purpose  of  excluding  surface-water,  to  which  end  it 
should  extend  well  into  the  solid  stratum  below.  Where  artesian  con- 
ditions exist  and  the  water  will  eventually  stand  higher  in  the  well  than 
the  adjacent  ground-water,  the  casing  must  extend  into  and  make  a 
tight  joint  with  the  impervious  stratum,  otherwise  water  will  escape 
into  the  ground  above. 

A  reliable  joint  can  best  be  made  by  sinking  a  smaller  tube  inside 
the  outer  one,  and  filling  the  space  between  it  and  the  well  or  outer 
tube  by  some  form  of  packing.  Rubber  packing-rings  are  used  for  this 
purpose,  which  if  well  placed  are  very  effective.  They  are  hollow 
cylinders  of  soft  rubber  inserted  in  an  adjustable  length  of  tubing  of  a 
diameter  smaller  than  the  well,  and  when  lowered  to  the  proper  place 
are  expanded  to  fill  the  annular  space  by  screwing  up  the  tubing. 
Linseed  bags  wrapped  around  the  tubing  have  been  much  used  for 
packing.  The  seed  expands  as  it  becomes  water-soaked  and  so  fills 
the  space.  Lead  packing  has  also  been  used  with  satisfactory  results. 
It  is  first  cast  around  the  end  of  the  pipe,  the  pipe  lowered  in  place, 
and  the  joint  made  by  driving  the  pipe  firmly  into  the  hole,  which  has 
previously  been  reamed  out  smooth. 

If  two  or  more  water-bearing  strata  are  encountered,  the  water- 
pressures  in  the  different  strata  are  likely  to  be  different,  that  from  the 
lower  usually  being  the  greater.  If  it  is  desired  to  utilize  only  the 
water  from  the  lower  stratum  at  its  maximum  head,  it  will  be  necessary 
to  place  the  packing  in  the  impervious  stratum  immediately  overlying 
the  one  in  question.  Otherwise  the  head  attained  will  be  more  nearly 

*  Eng.  News,  1888,  xix.  p.  488. 
t  Proc.  Inst.  C.  E.,  xc.  p.  33. 


DEEP  AND  ARTESIAN  WELLS.  313 

that  of  the  upper  strata.  Where  different  pressures  thus  exist  it  is  only 
possible  to  determine  their  amount  by  separately  testing  each  stratum 
as  reached,  the  others  being  cased  off.  This  operation  is  an  essential 
part  of  the  boring  and  should  be  carefully  performed.  Important  differ- 
ences in  quality  are  also  often  discovered  in  this  way. 

In  placing  permanent  packing  it  does  not  necessarily  follow  that 
certain  strata  should  be  excluded  because  of  a  less  static  head  than 
others.  None  need  be  excluded  from  which  the  head  is  greater  than 
the  head  existing  at  the  level  of  the  stratum  when  the  works  are  in 
operation.  The  question,  therefore,  depends  upon  the  amount  it  is 
proposed  to  lower  the  water  by  pumping. 

Ordinary  artesian  well  casing  is  made  of  light-weight  wrought-iron 
lap-welded  pipe.  For  pipe  which  is  to  be  driven  the  standard 
wrought-iron  pipe  is  ordinarily  used,  but  for  heavy  driving  extra  strong 
pipe  is  necessary.  Joints  of  drive  pipe  should  be  made  so  that  the 
ends  of  the  tubing  are  in  contact  when  screwed  up.  The  life  of  a  good 
heavy  pipe  is  ordinarily  very  great,  but  cases  have  occurred  where  the 
pipe  has  been  rapidly  corroded,  due  to  the  presence  of  excessive 
amounts  of  carbonic  acid. 

349.  Cost. — The  cost  of  sinking  wells  will  of  course  vary  greatly 
according  to    locality,   nature  of   strata,   and  depth  and   size  of  well. 
For  wells  6  to  8  inches  in  diameter  and  sunk  in  ordinary  rock  the  cost 
per  foot,  not  including  casing,  will   usually  range  from  $2.00  to  $3.00 
for  depths  of   500  feet,  up  to  $3.00  to  $5.00  for  depths  'of  2000  feet. 
For  smaller  sizes  the  cost   will  be  somewhat  less,  especially  for  the 
shallow  depths.     In  the  Dakotas  2-inch  wells  have  been  sunk  285  feet 
for  42  cents  per  foot,  and  forty-two  such  wells  with  an  average  depth 
of  322  feet  had  an  average  cost  of  78  cents  per  foot.     Six-inch  wells 
cost  from  $5.00  to  $6.00   per  foot   complete  for  depths  of    500  to 
1000  feet.* 

In  soft  material  the  cost  for  small  depths  will  be  somewhat  lower 
than  in  rock,  but  for  great  depths  much  higher,  on  account  of  the 
difficulty  of  sinking. 

For  sizes  much  exceeding  12  inches  the  cost  will  rapidly  increase. 
The  cost  of  the  large  6-foot  wells  at  Southampton  already  referred  to 
was  about  $25.00  per  foot  for  boring,  and  $20.00  for  casing. 

350.  Arrangement. — The  best  arrangement  of  deep  wells  is  in  a 
straight  line  at  right  angles  to  the  line  of  flow,  but  the  latter  point  is 
of  much  less  importance  than  with  shallow  wells  in  a  limited  water- 

*  Eleventh  Census,  Report  on  Agriculture  by  Irrigation. 


314  WORKS  FOR    THE   COLLECTION  OF  GROUND-WATER. 

bearing  stratum ;  as,  owing  to  the  lateral  extent  of  the  strata  and  slight 
inclination  of  the  hydraulic  grade-line,  water  will  flow  towards  a  small 
group  of  wells  nearly  equally  from  all  directions. 

351.  Size  and  Spacing. — The  high  cost  of  deep  wells  renders  a 
thorough  preliminary  investigation  relative  to  proper  size  and  spacing 
impracticable,  but  for  the  same  reason,  a  correct  determination  of  these 
points  is  of  great  importance.  The  desired  knowledge  must  be  got  by 
a  study  of  similar  plants,  or  gained  as  the  sinking  of  the  wells  pro- 
gresses. 

To  be  able  to  draw  correct  inferences  from  tests  of  artesian  wells  it 
is  very  essential  that  water  from  the  upper  strata  be  carefully  excluded. 
Static  heads  can  then  be  measured  by  allowing  the  water  to  rise  in  an 
open  pipe,  or  by  means  of  a  gauge.  The  difference  between  this  static 
head  and  the  head  measured  when  the  well  is  flowing  or  being  pumped 
from  is  then  partly  consumed  in  overcoming  friction  in  the  well  and 
partly  in  forcing  water  into  the  well  through  the  porous  strata.  The 
effect  of  a  change  in  size  of  well  and  of  head  can  then  be  readily 
estimated,  in  accordance  with  the  principles  of  Art.  311.  As  a  valu- 
able aid  in  such  calculations  the  flow  at  different  heads  should  be 
determined  and  a  discharge  curve  drawn.  This  gives  directly  the 
effect  of  variation  of  head  in  the  particular  well  tested,  and  also  enables 
the  matter  of  friction  to  be  more  accurately  determined. 

The  economical  spacing  for  deep  wells  will  be  much  greater  than 
for  shallow  wells.  It  will  likewise  pay  to  spend  much  more  money  in 
lowering  the  flow-line  by  making  deep  connections,  thus  decreasing 
the  number  of  wells  and  increasing  the  spacing.  The  questions  of 
size,  spacing,  and  connections  are  interdependent,  and  also  depend 
upon  the  economy  of  different  types  of  pumps ;  and  a  correct  solution 
requires  a  careful  study  of  these  questions,  together  with  many 
others  depending  upon  local  conditions.  It  will  often  be  necessary  to 
estimate  on  several  different  arrangements  before  the  best  one  is 
arrived  at. 

Spacings  in  some  carefully  constructed  works  which  have  apparently 
given  satisfactory  results  are :  At  Galveston,  Texas,  thirty  7-in. 
wells,  about  800  feet  deep  and  560  feet  apart,  yield  about  250,000 
gallons  per  well.  At  Memphis,  forty-two  6-  and  8 -inch  wells  about 
400  feet  deep  were  spaced  at  first  75  feet  apart  and  afterwards  2 50  feet. 
Maximum  flow  =  about  250,000  gallons  per  well.  At  Savannah,  Ga., 
12-inch  wells  500  feet  deep  were  spaced  300  feet  apart.  Yield  = 

*  Eleventh  Census,  Report  on  Agriculture  by  Irrigation. 


DEEP  AND  ARTESIAN    WELLS.  315' 

about  800,000  gallons  per  day  per  well.  At  Galveston,  the  connec- 
tions were  made  at  a  slight  depth  below  the  surface ;  at  Memphis,  in 
a  tunnel  80  to  90  feet  deep ;  and  at  Savannah,  in  a  conduit  20  feet  deep. 
At  Fort  Worth,  Texas,  thirteen  8-inch  wells  1000  feet  deep  were  placed 
800  feet  apart.  The  total  yield  was  about  1,000,000  gallons,  although 
the  first  two  or  three  wells  indicated  a  total  of  3,000,000  gallons.  At 
Madison,  Wisconsin,  a  spacing  of  600  to  800  feet  is  found  desirable  for 
wells  in  the  Potsdam  sandstone  when  operated  under  about  15  feet  of 
head.  The  yield  under  these  conditions  is  about  300,000  gallons  per 
day  each. 

352.  Methods  of  Operation.  —  On  account  of  the  relatively  great  cost 
of  deep  wells  it  will  often  be  found  economical  to  so  arrange  the  pumps 
and  connections  that  a  considerable  lowering  of  the  water-level  below 
the  ground-surface  may  be  obtained.  This  is  generally  accomplished 
by  connecting  all  the  wells  to  a  single  pump  or  set  of  pumps,  placed 
at  a  greater  or  less  depth  below  the  surface.  Where  the  connections 
are  very  deep  tunneling  may  have  to  be  resorted  to.  Another 
common  method  of  drawing  water  from  deep  wells  in  the  case  of  small 
plants  is  by  the  use  of  a  separate  deep-well  pump  for  each  well.  The 
usual  type  of  deep-well  reciprocating  pump  used  in  such  cases  is  gen- 
erally of  very  low  efficiency  and  small  capacity  and  not  adapted  to  large 
supplies.  The  air-lift  is  also  of  comparatively  low  efficiency,  but  is  a 
very  flexible  system,  and  in  many  cases  can  be  used  to  advantage  in 
relatively  large  works.  Where  the  yield  per  well  is  large  the  most 
economical  method  of  deep  pumping  is  probably  the  use  of  the  small 
multiple-stage  centrifugal  pump.  These  pumps  are  made  to  fit  casings 
of  15  to  2O-inch  diameter  and  may-  conveniently  be  direct-connected 
to  vertical  electric  motors  operated  from  a  central  station.  The  well 
need  be  made  of  the  large  size  only  to  the  depth  desired  for  the  pump. 
(For  further  discussion  of  the  question  of  pumping  machinery  see 
Chapter  XXVI.) 

353.  Examples  of  Artesian-well  Plants.  —  In  the  majority  of  cases  an 
artesian-well  plant,  where  consisting  of  several  wells,  is  operated  in  the  same 
way  as  a  system  of  shallow  wells,  a  good  illustration  of  which  is  the  Plainfield 
works  described  on  page  307.  Two  noteworthy  exceptions  to  this  arrange- 
ment are  the  large  works  at  Memphis,  Tenn.,  and  at  Rockford,  111.,  —  plants 
which  represent  the  most  modern  practice  in  this  branch  of  water-works 
engineering. 

The  supply  at  Memphis  is  obtained  from  a  series  of  forty-two  wells  sunk 
about  400  feet  deep  to  a  stratum  of  water-bearing  sand.  Little  natural  flow 
was  obtained,  and,  to  increase  the  yield,  the  pumps  were  located  in  a  pump- 
pit  about  50  feet  deep  and  connections  made  with  the  wells  by  means  of 
tunnels.  Vertical  compound  engines  were  adopted  haying  a  duty  of  about 


3i6 


WORKS  FOR    THE   COLLECTION  Of   GROUND-WATER. 


115,000,000  foot-pounds  per  1000  pounds  of  steam.*     Mr.  T.  T.  Johnston 
was  the  engineer. 

A  later  example  and  one  involving  several  interesting  features  is  the  plant 
at  Rockford,    111.,    Mr.    D.    W.   Mead,    Mem.   Am.    Soc.   C.   E.,   engineer. 


Baft  of    Shaft    Showing 
Airsngpment  of  Eroines 


Vertical  Section  of  Shaft. 


Section   of  Shaft-   Showing 
of    Pumps. 


FIG.  62. — PUMP-SHAFT  AND  PUMPS,   ROCKFORD,  ILL. 

(From  Engineering  Nevus,  vol.  XLII.) 

Previous  to  1898  the  city  had  been  supplied  for  some  years  by  artesian  wells, 
part  sunk  to  the  Potsdam  sandstone  and  part  into  the  St.  Peter  (see  Fig. 
42,  page  112).  Increased  demand  necessitated  increased  lowering  of  the 


*  Eng.  Record,  1891,  xxiv.  p.  234. 


DEEP  AND   ARTESIAN    WELLS.  317 

water-level,  a  result  temporarily  accomplished  by  means  of  deep-well  pumps 
and  by  the  air-lift.  The  arrangement  adopted  for  the  new  plant  was  to  sink 
a  shaft  95  feet  deep,  place  pumps  therein,  and  connect  them  to  the  various 
wells  through  tunnels  constructed  from  the  bottom  of  the  shaft.  The  arrange- 
ment is  clearly  shown  in  Fig.  62.  The  shaft  is  water-tight,  with  a  floor  of 
concrete,  and  the  lateral  tunnels  are  filled  with  concrete,  put  in  after  the 
suction-pipes  were  placed.  The  two  pumps,  each  of  3  million  gallons 
ordinary  capacity,  are  of  the  centrifugal  type  and  are  operated  through  rope 
transmission  by  compound  engines  placed  at  the  surface.  Under  a  head  of 
over  100  feet  the  pumps  alone  developed  an  efficiency  of  from  70  to  75  per 
cent,  and  the  whole  plant  a  duty  of  58,000,000  foot-pounds  per  1000  pounds 
of  dry  steam.  For  further  data  regarding  these  pumps  see  Chapter  XXVI. 

354.  Yields. — In  making  estimates  regarding  flow  it  is  important 
to  bear  in  mind  that  it  requires  a  considerable  length  of  time  to  deter- 
mine with  certainty  the  adequacy  of  the  supply,  and  furthermore  that 
the  sinking  of  wells  by  other  interests,  even  though  at  considerable 
distances,  may  very  seriously  affect  the  yield.      The  amount  of  water 
flowing  through  a  porous  rock,  per  square  foot  of  cross-section,  is  likely 
to  be  very  much  less  than  that  which  is  often  found  in  coarse  sand  and 
gravel  strata.     The  slope  of  the  hydraulic  grade-line  in  the  former  case 
is  usually  very  much  less  and  the  friction  much  greater,  large  volumes 
depending  on  great  thickness  and  breadth  of  strata.      Detailed  figures 
relating  to  yield  for  several  supplies  have  been  given  on  page    315. 
Where  conditions  are  sufficiently  favorable  for  works  of  some  magni- 
tude the  yield  per  well  under  a  moderate  head  ranges   from  about 
150,000  gallons  per  day  to  800,000  gallons,  or  even  more.     With 
yields  of  less  than  100,000  gallons  per  day,  works  for  developing  large 
quantities  become  very  expensive,  relatively  more  expensive  than  for 
small  quantities,   since  with  a  large  number   of  wells   there  is  much 
greater  interference. 

355.  Failure  of  Wells. — The  chief  cause  of  a  decrease  in  yield  of  a 
well  is  the  influence  of  other  wells  sunk  in  the  vicinity.      This  effect  is 
likely  to  be  felt  much  farther  than  when  similar  quantities  are  drawn 
from  gravel  strata,  on  account  of  the  great  depth  to  which  the  head, 
or  flow-line,  is  often  reduced  in  deep  wells  by  pumping.      The  case 
of  the  failure    of  wells    in  the  vicinity  of  Chicago,   and  its  effect  for 
several  miles  around,  has  already  been  mentioned.      At  Savannah  it  is 
estimated  that  the  withdrawal  of  10  million  gallons  per  day  affects  the 
pressure  for  8  miles  distant.      At   Dubuque,  Iowa,  a  large  well  bored 
on  low  ground  caused  the  flow  from  several  wells  higher  up  to  cease 
entirely.      At  Denver  the  flow  has  also  greatly  decreased  and  varies 
with  the  season. 

The  yield  of  a  well  may  also  decrease  on  account  of  causes  inherent 


WORKS  FOR    THE    COLLECTION  OF  GROUND-WATER. 


in  the  well  itself.  One  such  cause  is  leakage  due  to  defective  packing, 
this  being  a  common  fault  of  wells  in  the  Dakota  basin.  Another 
cause  of  partial  failure  is  by  clogging  through  the  inflowing  of  fine 
sand.  This  can  be  removed  by  the  methods  described  on  page  306. 

The  gradual  lowering  of  head  due  to  long-continued  operation  is  well 
illustrated  by  Fig.  63  which  represents  the  conditions  at  Memphis.*  In 
a  report  of  a  Commission  of  Engineers  in  1902  it  is  stated  that  in  1898 
the  pumpage  was  about  19,000,000  gallons  per  day,  and  in  1902  about 


Distances  from   Pumping  ,  Station     in   Feet- 


FIG.  63.  —  GROUND-WATER  CURVES  AT  MEMPHIS,  TENN. 

(From  Engineering  Record,  vol.  XLVI.) 

12,000,000  gallons.  It  is  estimated  that  a  second  station  and  group  of 
wells  might  be  established  about  four  miles  distant  with  a  maximum 
capacity  of  each  group  of  about  1 5,000,000  gallons  per  day  under  a 
head  of  about  60  feet. 

HORIZONTAL    GALLERIES    AND    WELLS. 

356.  Filter-galleries. — Where  ground- water  can  be  reached  at  mod- 
erate depths  it  is  sometimes  intercepted  by  galleries  constructed  across 
the  line  of  flow.  If  these  are  placed  at  a  sufficient  depth  they  will 
evidently  enable  the  entire  flow  of  the  ground- water  to  be  intercepted. 
In  form  a  gallery  may  consist  merely  of  an  open  ditch  which  leads 
the  water  away,  or  it  may  be  a  closed  conduit  of  masonry,  wood,  iron, 
or  vitrified  clay  pipe,  provided  with  numerous  small  openings  to  allow 
the  entrance  of  the  water.  Unless  constantly  submerged,  wood  should 
not  be  used.  Masonry  and  vitrified  pipe  are  preferable  to  iron,  as  these 
materials  are  uninjured  by  exposure  to  water.  If  galleries  are  not 
covered,  excessive  vegetable  growth  is  apt  to  occur  which  may  injure 
the  quality  of  the  water. 

Galleries  are  usually  constructed  in  open  trench.  To  prevent  the 
entrance  of  fine  material  the  back-filling  near  the  openings  should  be 

*  Eng.  Record,  1902,  XLVI.  p.  514. 


HORIZONTAL    GALLERIES  AND    WELLS.  319 

of  gravel  of  graded  size,  and  as  an  additional  precaution  the  openings 
may  be  made  in  the  bottom  only.  Manholes  should  be  provided  to 
permit  of  inspection  and  cleaning.  Galleries  need  be  of  a  size  only 
large  enough  to  carry  the  estimated  quantity,  or,  in  case  trouble  with 
sand  is  feared,  large  enough  to  permit  of  inspection.  They  are 
arranged  to  lead  the  water  to  the  pump-well,  and  may  be  provided  with 
gates  so  that  the  water  may  be  shut  off  from  various  sections. 

The  cost  of  galleries  is  about  the  same  as  that  of  sewers  in  similar 
ground.  It  increases  rapidly  with  the  depth,  but  up  to  a  depth  of  20 
or  25  feet  it  is  sufficiently  low  so  that  the  construction  of  galleries  can 
often  be  advantageously  undertaken.  A  gallery  not  only  intercepts  the 
water  more  completely  than  wells,  but  it  replaces  the  suction-pipe,  it  is 
more  durable  than  either  pipe  or  wells,  and  all  trouble  from  the  pumping 
of  air  is  avoided. 

Where  conditions  are  favorable  surface-water  may  sometimes  be 
used  to  augment  a  ground-water  supply,  thus  using  the  natural  soil  as  a 
filter  instead  of  constructing  an  artificial  filter.  This  system  would  be 
suitable  only  for  removing  suspended  matter  as  it  would  be  too  unreli- 
able to  deal  with  sewage  polluted  water. 

357.  Examples. — There  are  comparatively  few  cases  in  this  country 
where  galleries  have  been  used  to  intercept  ground-water  proper,  they  being 
mainly  used  to  collect  filtered  stream-water  as  explained  in  Art.  359.  As  an 
example  of  their  use  for  ground-water  collectors,  mention  may  be  made  of  the 
gallery  at  Naples,  Italy.  The  supply  there  is  taken  from  a  gravel  stratum 
10  to  13  feet  thick,  overlaid  by  30  feet  of  clay.  The  gallery  is  2000  feet  long. 
It  was  constructed  in  open  trench  and  back-filled  with  gravel  and  clay.  The 
yield  is  38  million  gallons  per  day.* 

The  city  of  Munich,  Germany,  gets  its  water-supply  from  springs  and 
collecting-galleries  in  the  foothills  of  the  Alps.  The  water  occurs  in  a  deposit 
of  gravel  resting  upon  a  bed  of  sandstone,  and  is  intercepted  by  collecting- 
tunnels  driven  nearly  horizontally,  and  located  partly  in  the  sandstone  and 
partly  in  the  overlying  gravel.  From  these  galleries  the  water  is  conveyed  to 
an  aqueduct  leading  to  the  city.  Fig.  64  shows  the  general  arrangement  and 
an  enlarged  cross-section  of  a  collecting-tunnel.t 

Karlsruhe  obtains  its  water-supply  from  an  old  river-bed  filled  with  gravel, 
the  water  is  impounded  by  a  clay  wall  or  dam  and  collected  by  a  gallery 
which  yields  1,600,000  gallons  per  day.$ 

Many  cities  in  Holland  secure  their  supplies  from  open  ditches  and 
galleries  in  the  sand-dunes.  Amsterdam  collects  in  this  way  about  10  inches 
out  of  a  total  rainfall  of  30  inches  per  year.  Other  yields  have  been  obtained 
as  high  as  20  to  25  inches. 

Galleries  have  been  constructed  at  several  places  in  the  West  for  collecting 

*  Proc.  Inst.  C.  E.,  LXXXIV.  p.  468. 
t  Eng.  Record,  1898,  xxxvni.  p.  78. 
\  Jour.f.  Gasbel.  u.  Wasservers.,  1894,  p.  269. 


320          WORKS  FOR    THE   COLLECTION  OF  GROUND-WATER. 

water  from  the  large  gravel  deposits  beneath  and  adjacent  to  the  streams. 
Such  are  the  older  works  of  Denver*  and  of  Golden,!  Colorado,  and  Eureka,  \ 
Cal.  These  galleries  usually  consist  of  wooden  boxes  or  cribs  constructed  at 
a  considerable  depth  in  the  water-bearing  gravel,  and  are  often  arranged  to 


(JSravtl. 


.  Water  Bearing  Gravel. 
/•!•  ^.-;:.r-->.v^<i'i«fv  -X-yAff 

I..v.VV<.  .".:-,.  •  •••:-.•.;•..:'.••-•  '.•-•-••'-•' 


Laid  Dry. 


FIG.  64.— COLLECTING-GALLERIES,  MUNICH  WATER-WORKS. 

(From  Engineering  Record,  vol.  xxxvm.) 

collect  not  only  ground-water  but  filtered  surface-water  from  the  streams. 
At  Eureka  provision  is  made  for  back-flushing. 

Los  Angeles  obtains  its  supply  of  about  26,000,000  gallons  per  day  from 
galleries  in  the  underflow.  Vitrified  pipe  and  concrete  galleries  are  used.§ 

At  Daggett,  Cal.,  water  for  irrigation  is  obtained  from  underground 
streams  by  means  of  a  flume,  the  water  being  dammed  up  by  sheet-piling 
driven  across  the  line  of  flow.  Surface-water  flows  here  also  after  heavy 
storms.  || 

Another  notable  case  of  a  subsurface  dam  is  that  at  Pacoima  Creek,  Col. 
Here  the  dam  is  from  25  to  50  feet  deep  and  consists  of  a  two-foot  concrete 
well.  The  water  is  collected  by  means  of  horizontal  rows  of  concrete  pipes 
laid  about  10  feet  apart  and  leading  to  two  collecting  wells.1[ 

358.  Tunnels  in  Rock. — Galleries  for  collecting  ground-water  are 
occasionally  tunneled  in  solid  rock.  This  may  happen  along  a  side 
hill  where  an  outcropping  porous  stratum  overlies  an  impervious  one 
and  it  is  desired  to  develop  the  flow  by  running  a  tunnel  along  the  hill 
near  the  bottom  of  the  porous  stratum. 

Tunnels  or  galleries  are  also  sometimes  run  from  the  bottom  of 
large  wells  for  the  purpose  of  increasing  the  yield.  This  method  of 

*  Trans.  Am.  Soc.  C.  E.  1894,  xxxi.  p.  135. 
t  Eng.  News,  1891,  xxv.  p.  610. 
\  Ibid.,  p.  339. 
§  Ibid.,  1906,  LV.  p.  595. 
II  Ibid.,  1896,  xxxvi.  p.  157. 

IF  W.  S.  Paper,  No.  69,  U.  S.  G.  S.,  1902  ;  also  Eighteenth  Annual  Report, 
U.  S.  G.  S.,  Part  IV,  p.  693. 


HORIZONTAL    GALLERIES  AND    WELLS,  321 

increasing  the  flow  is  advantageous  where  it  is  necessary  to  lower  the 
pumps  and  to  concentrate  the  flow  in  a  single  well. 

359.  Wells  and  Galleries  Near  Streams. — Wells  and  galleries  are 
often  constructed  near  streams  for  the  purpose  of  getting  all  or  a  por- 
tion of  the  supply  therefrom;  and,  on  the  other  hand,  it  often  happens 
that  wells  sunk  near  streams  obtain  much  of  their  water  from  them 
when  they  are  supposed  to  get  it  all  from  the  opposite  direction.  In- 
general  the  natural  ground-water  surface  will  slope  towards  a  stream 
as  shown  in  Fig.  17,  page  90;  and  until  a  well  is  pumped  from,  the 
water-level  therein  will  stand  higher  than  the  surface  of  the  water  in 
the  stream.  The  amount  the  water  in  the  well  can  now  be  lowered 
without  drawing  from  the  river  depends  upon  the  distance  of  the  well 
from  the  stream  and  upon  the  ground-water  slope;  but  no  water  can 
enter  from  the  river  so  long  as  there  is  a  summit  in  the  ground-water 
surface  between  the  stream  and  well.  A  few  test-borings  placed 
between  the  well  and  stream  will  determine  this  point.  The  source  of 
water  can  also  often  be  determined  by  chemical  analysis. 

Where  wells  or  galleries  are  placed  near  streams  for  the  purpose  of 
obtaining  surface-water  filtered  through  the  ground,  the  success  of  such 
works  depends  much  upon  the  character  of  the  river-bottom.  Even 
when  the  lower  strata  are*  porous,  the  river,  if  a  silt-bearing  one,  may 
have  a  nearly  impervious  bottom  and  the  natural  filter  will  only  become 
more  clogged  by  use,  necessitating  perhaps  the  abandonment  of  the 
collecting-works.  Such  failures  have  occurred  in  some  instances.  With 
a  sandy  river-bottom  kept  clean  by  the  scouring  action  of  the  floods, 
and  with  a  porous  substratum,  works  of  this  kind  will  give  good  results. 
To  secure  good  filtration  the  works  should  be  located  at  least  50  feet 
and  preferably  a  greater  distance  from  the  stream.  Galleries  of  the 
kind  here  considered  have  sometimes  been  built  of  great  width,  but,  as 
most  of  the  filtration  must  be  lateral,  very  little  is  gained  by  increasing 
the  width  over  that  required  for  convenience  in  construction  and 
inspection. 

The  city  of  Painsville,  O.,  has  adopted  this  method  of  securing 
iter  from  Lake  Erie.  Wooden  galleries  500  feet  long  constructed 
:lose  to  the  lake  receive  about  1,000,000  gallons  per  day.*  Galleries 
ire  also  successfully  used  at  Laredo,  Texas,  under  a  sandy  island  in  the 
.io  Grande  river. f 

At  Nancy,  France,  a  system  of  double  filtration  has  been  devised  to 

*  Eng.  Record,  IQOI^XLIII.  p.  518. 
t  Ibid.,  Jan.  9,  1904. 


'322  WORKS  FOR    THE    COLLECTION  OF  GROUND-WATER. 

overcome  difficulties  due  to  the  silting  up  of  the  original  collecting 
galleries  receiving  water  from  the  river.  The  river-water  now  passes 
through  a  rough  filter  of  coarse  gravel  and  thence  into  a  long  distribu- 
ting chamber  whence  it  flows  through  the  natural  sand  and  gravel  to 
the  filter  gallery.  * 

The  yield  of  a  series  of  wells  or  of  a  gallery  collecting  filtered  sur- 
face-water will  be,  as  in  the  case  previously  discussed,  proportional  to 
the  lowering  of  the  water-level,  or  to  the  head  on  the  filter,  and  will  be 
nearly  proportional  to  the  length  of  the  line  of  works.  In  gallons  per 
day  per  100  feet  of  gallery,  the  yield  from  various  successful  works 
varies  from  30,000  to  1,000,000  or  more,  which  is  about  the  same  as  is 
obtained  from  lines  of  wells. 

360.  Horizontal  or  Push  Wells  are  tubular  wells  pushed   approxi- 
mately horizontally  into  a  water-bearing  stratum,  or  under  the   bed  of 
a  lake  or  stream.     They  are  forced  into  the  ground  from  a  trench  by 
means  of  jacks  braced  against  the   opposite    side.     These  wells   have 
been  most  successful  when  extended  out  under  a  body  of  water.     At 
South  Haven,  Mich.,  three   6-inch    Cook  wells  with  3O-foot   strainers 
were  pushed  out   150  feet  under  Lake  Michigan.     The  wells  were  25 
feet  apart   and  yielded    1,250,000  gallons  per    day.     Another    similar 
plant  at  Crystal  City,  Mo.,  consisted  of  two  8-inch  wells  with  65  feet 
of  strainer,  extending  200  feet  under  the  Mississippi  River  in  a  sand 
stratum  20  feet  thick.     The  yield  was  1,300,000  gallons  per  day.f 

361.  Filter-cribs. —  Another  method  of  utilizing  a  river-bottom  as 
a  natural  filter  is  to  construct  a  wooden  crib  in  an  excavation  in  the 
bed  of  the  stream,  fill  it  with  graded  gravel  and  then  cover  the  struc- 
ture with  3   or  4  feet  of  sand  up  even  with  the  river-bottom.     The 
suction-pipe    then   leads  from  the  crib  to  the  pumps.     This    form   of 
construction  is  well  adapted  to  sandy-bottom  streams  with  swift    cur- 
rents and  has  proved  a  very  efficient  way  of  clarifying  muddy  river- 
waters.     The  rate   of   filtration   through    such   a  filter   may  be   quite 
closely  estimated   according    to   the   principles   explained   in  Chapter 
XXI. 

In  Fig.  65  is  illustrated  a  crib  at  Kensington,  Pa.,  similar  to  several 
which  have  been  constructed  in  the  Allegheny  River.  This  crib 
is  200  feet  long,  32  feet  wide,  and  4  feet  high,  and  is  covered  with 
4  feet  of  gravel  and  sand  dredged  from  the  river-bottom.  It  is 
designed  for  a  capacity  of  3  million  gallons  per  day,  equal  to  a  rate  of 

*  Eng.  Record,  1905,  LI.    p.  148. 
t  Eng.  News,  1893,  xxix.  p.  452. 


HORIZONTAL    GALLERIES  AND    WELLS. 


323 


filtration  of  about  16  million  gallons  per  acre  per  day.     The  estimated 
cost   is   $2400   per   million   gallons  capacity.     Provision   is   made  for 


FIG.  65. — FILTER-CRIB,  KENSINGTON,  PA. 

(From  Engineering  News,  vol.  xxxi.) 


cleaning  by  back-flushing.  The  system  was  designed  by  Mr.  James 
H.  Harlow,  Mem.  Am.  Soc.  C.  E.  The  cribs  are  usually  placed 
where  the  velocity  of  the  current  is  from  4  to  8  feet  per  second  and 
little  trouble  has  been  experienced  through  clogging. 

Filters  of  this  sort  are  found  to  clarify  the  water  at  most  times  quite 
satisfactorily,  but  the  bacterial  content  of  the  water  is  but  little 
changed.  The  hardness  is  likely  to  be  increased. 

LITERATURE. 


GENERAL    ARTICLES. 

1.  Oelwein.     Gewinnung  des  Grundwassers  fur  die  Wasserversorgung  von 

Sternberg  und  Witkowitz  in  Mahren.     Zeit.  Oest.  Ing.  u.  Arch. 
Ver.,  1900,  LII.  p.  753. 

2.  Methods  of  Intercepting  Ground-water.     Report  of  the  Commission  on 

Additional  Water-supply  for  New  York  City,  1904,  App.  vn.  p.  835. 

3.  de   Varona.     Proposed    Further  Development  of   Underground    Water- 

supply  for  Brooklyn.     Report  N.  Y.  Dept.  Water-supply;  Gas  and 
Electricity,  June  30,  1902.     Eng.  News,  1902,  XLVIII.  p.  304. 

4.  Richert.     The    Progressive    Sinking   of    the   Ground-water   Level    and 

Artificial  Ground-water  Supplies.     Eng.    News,  1904,  LII.  p.  474. 

5.  Kirchoffer.     The  Sources  of  Water-supply  in  Wisconsin.     Bui.  Univ.  of 

Wis.,  No.  106,  Jan.  1906. 

SPRINGS. 

1.  Berger.     Der  Kaiser  Franz  Josef s-Hochquellenleitung.     Zett.  Oest.  Ing. 

u.  Arch.    Ver.,  1901,  LIII.  p.  33. 

2.  Ledy.    Captage  de  Sources,  Dispositif  Adopte*  a  Brest.    An.  des  Fonts 

et  Ch.,  1906,  2  Trim.,  xxn.  p.  275. 


'324  WORKS  FOR    THE   COLLECTION  OF  GROUND-WATER. 


LARGE    OPEN    WELLS. 

1.  Matthews.    The  Wells    and  Borings  of   the  Southampton  Water-works 

Proc.  Inst.  C.  E.,  1886,  xc.  p.  33. 

2.  Winslow.    Water-supply  of   Waltham.      Jour.    New  Eng.  W.  W.  Assn., 

1893,  VIIL  p.   118. 

3.  Fuller.    A    Description    of   the    Water-works    at  Webster,    Mass.    Jour. 

New  Eng.  W.  W.  Assn.,   1895,  ix.  p.  240. 

4.  Labelle.     Auxiliary  Supply  of  the  Water-works  of  Addison,  N.  Y.    Eng. 

News,  1895,  xxxin.  p.  163. 

5.  Sinking  a  large  Supply-well  for  the  Water-works  of  Canton,  Mass.     Eng. 

News,  1896,  xxxvi.  p.  211. 

DRIVEN    WELLS. 

1.  Noyes.     The  Driven-well  System  as  a  Source  of,  or  a  Means  of  Obtaining, 

a  Water-supply.     Jour.  New  Eng.  W.  W.  Assn.,  June,  1887.     Eng. 
Record,  1887,  xvi.  p.  264. 

2.  The  Maiden  Water- works.     Eng.  Record,  1889,  xx.  p.  303. 

3.  Forbes.     Driven  wells   as  a    Source  of    Water-supply.    Jour.  New  Eng. 

W.  W.  Assn.,  1891,  v.  p.  141. 

4.  The  Driven-well  System   of    Schuyler,  Neb.    Eng.  News,   1892,  xxvm. 

p.   199. 

5.  Extension   of   the    Driven   Wells   of    the    Maiden  Water-works    System 

Eng.  Record,  1893,  xxvn.  p.  399. 

6.  The  Foxboro,  Mass.  Water-works.     Eng.  Record,  1893,  xxvu.  p.  456. 

7.  McElroy.     Supply-wells  for  Brooklyn,  N.  Y.      Proc.  Am.  W.  W.  Assn., 

1893,  xin.  p.  13. 

8.  Tribus.     Driven  Wells   of   the    Plainfield  Water-supply  System.    Trans. 

Am.   Soc.  C.  E.,  1894,  xxxi.  p.  371. 

9.  Bowers.     Experiments  with  Tube  Wells   at   Lowell,  Mass.    Jour.   New 

Eng.  W.  W.  Assn.,  1894,  ix.  p.  67. 

10.  Bowers.     Description  of  Second  Tube-well  Plant  at  Lowell,  Mass.    Jour. 

New  Eng.  W.  W.  Assn.,  1896,  x.  p.  226. 

11.  Hague.      Central   Water-supply    Stations  for    Railways.      Eng.    News, 

1896,  xxxv.  p.  114. 

12.  Forbes.     Driven    Wells    at   Brookline,   Mass.    Jour.    New    Eng.  W.   W. 

Assn.,  1897,  xi.  p.  195. 

13.  Bowers.     Result  of    Tube-well  Experiments  in  Lowell,  Mass.    Jour.  New 

Eng.  W.  W.  Assn.,  1898,  xin.  p.  30. 

14.  Sinking  Driven  Wells.    Eng.  Record,  1899,  XL.  p.  362. 

15.  The  Additional  Water-supply  of  Middleton,  Ohio.    Eng.  News,   1904, 

LIII.  p.  122. 

1 6.  Maury.    The    New  Well    and    Hydraulic    Pumping  Plant   at   Peona,  111. 

Eng.  Record,  1905,  LI.  p.  139. 

17.  Maury.     Strainers  for  Driven  Wells.     Eng.  News,  1906.  LV  p.  260. 

ARTESIAN    WELLS. 

i.  Darley.  Artesian  Wells.  Notes  on  Drilling  and  Boring  Artesian  Wells 
as  Practiced  in  the  United  States  of  America.  Engineering,  1885, 
XLI.  p.  683. 


LITERATURE. 

2.  Tweddle.     The  Boring  and  Sinking  of  Wells.    Engineering,  1888,  XLVI. 

p.  199. 

3.  The  Memphis,  Tenn.,  Water-works.     Eng.  Record,  1891,  xxiv.  p.  234. 

4.  Irrigation  by  Artesian  Wells.     Eng.  News,  1892,  xxvm.   p.  342.    Data 

of  cost. 

5.  St.  Augustine's  Artesian  Water.     Eng.  Nevus,  1892,  xxvn.  p.  182. 

6.  The  Deep  Artesian  Well  at  Galveston,  Tex.     Eng.  News,  1892,  xxvm. 

p.    122. 

7.  The  New  Artesian  Water-supply  at  Savannah,  Ga.     Eng.  News,  1893, 

xxix.  p.  527. 

8.  Fort  Smith,  Tex.,  Water-works.     Eng.  Record,  1894,  xxx.  p.  5. 

9.  Carpenter.     The  Effect  of  Neighboring  Artesian  Wells  on  each  Other. 

Eng.  News,  1895,  xxxiv.  p.  277. 

10.  The  Galveston  Water-works.     Eng.  Record,  1896,  xxxiv.  p.  122. 

11.  Johnston.     The    Restoration    of    the    Water-supply    at    Savannah,    Ga. 

Jour.  W.  Soc.  Eng.   1897,  n.  p.  711. 

12.  Johnston.     Discussion  on  Deep-well  pumping.     Jour.  West.  Soc.  Engrs., 

1897,  ii.  p.  190. 

13.  Jetting  Down  Artesian  Wells.     Eng.  Record,  1898,  xxxix.  p.  428. 

14.  The   Large  Artesian-well   Plant  at   Camden,  N.  J.     Eng.  Record,   1899, 

xxix.  p.  520. 

15.  The    New  Water-supply   System  of   Rockford,   111.     Eng.  News,    1899, 

XLII.  p.  18. 

1 6.  Forchheimer.     Die    Brunnen  der  Brauerei    in   Ottakring.     Sinking   and 

Lining  Deep  Wells.     Zeit.  d.    Oest.     Ing    u.   Arch.    Ver.,    1900, 
LII.  p.  693. 

17.  The  Kasusa  System  of  Artesian  Well  Boring   in  Japan.     Eng.  News, 

1902,  XLVIII   p.  165. 

1 8.  The  Artesian  Water-supply  of  Memphis,  Tenn.     Report  of  Engineering 

Board.     Eng.  Record,  1902,  XLVI.  p.  513. 

19.  Slichter.     The  California  or  "Stove-Pipe"  Method  of  Well  Construction 

for  Water-supply.     Eng.  News,  1903,  L.  p.  429. 

20.  The  New  Water- works  of  East  Orange,  N.  J.     Eng.  Record,   1904,  L. 

p.  484. 

2 1.  Getman.     The  New  Artesian  Water-supply  of  Ithaca,  N.  Y.     Eng.  News, 

1905,  LIII.  p.  412. 

FILTER-GALLERIES    AND    FILTER-CRIBS. 

1.  The -Naples  Water-works.     Proc.  Inst.  C.  E.,  1885,  LXXXIV.  p.  468. 

2.  The  Water-works    Extensions  at   Newton, '  Mass.     Eng.   Record,   1891, 

xxiv.  p.  418. 

3.  The  Reading,  Mass.,  Water-works.     Eng.  Record,  1892,  xxv.  p.  282. 

4.  Horizontal  Tubular  Wells  at  South  Haven,  Mich.     Eng.  News,   1893, 

xxix.  p.  452. 

5.  Lippincott.     Water   Development   on  the   Mojave  River,  near    Dagget, 

Cal.     Eng.  News,  1896,  xxxvi.  p.  157. 

6.  Fuertes.     The  Water-works  of  Munich,  Germany.     Eng.  Record,  1898^ 

xxxvin.  p.  78. 

7.  Filter-cribs  in  the  Allegheny  River,  near  Pittsburg,  Pa.    Eng.  News,  1898, 

xxxix.  D.  269. 


326  WORKS  FOR   THE   COLLECTION  OF  GROUND-WATER. 

8.  The  Filter-crib  of  the  Allegheny  Water-works.     Eng.  News,  1900,  XLIII. 

p.  328. 

9.  The  Filter-galleries  at   Painesville,  Ohio.     Eng.  Record,   1901,  XLIII.  p. 

518. 

10.  McLane.     The    Filter-galleries   for  the   Water-works  of  Laredo,  Texas. 

Eng.  Record,  1904,  XLIX.  p.  41. 

11.  Gieseler.      A   New   Form   of   Filter-gallery   at   Nancy,    France.      Eng. 

Record,  1905,  LI.  p.  148. 

12.  Mason.      The    Water-supply    of    Amsterdam,    Holland.      Eng.   News, 

1905,  LIII.  p.  437. 

13.  Hardesty.     The  Underground  Water-supply  of  the  City  of  Los  Angeles, 

Cal.     Eng.  News,  1906,  LV.  p.  595. 

14.  An    Infiltration    Water-works    Intake   Under    the   Ohio   River.      Eng. 

Record,  1907,  LVI.  p.  227. 


CHAPTER   XV. 
IMPOUNDING-RESERVOIRS. 

CAPACITY. 

362.  Use  and  Value  of  Storage. — Whenever  the  minimum  rate  of 
yield  of  a  source  of  water-supply  is  less  than  the  demand,  the  excess 
of  demand  over  supply  may  often  be  furnished  by  storing  up  the  sur- 
plus waters  during  periods  of  greater  yields.  In  the  case  of  surface- 
water  supplies  the  yield  is  very  variable,  and  a  large  amount  of  storage 
is  needed  to  make  available  even  50  per  cent  of  the  total  flow.  On 
the  other  hand  the  minimum  flow  is  relatively  so  small  that  a  compara- 
tively small  storage  is  sufficient  to  increase  many  times  the  capacity  of 
the  stream  to  deliver  uniform  quantities. 

The  artificial  storage  of  surface-water  in  large  volumes  is  usually 
accomplished  by  constructing  a  dam  across  the  valley  in  question,  thus 
forming  an  impounding-reservoir.  Frequently  it  will  be  impossible  or 
uneconomical  to  store  sufficient  water  in  a  single  reservoir,  in  which 
case  several  may  be  constructed  on  'the  same  or  different  watersheds, 
thus  forming  a  system  of  reservoirs.  Considerable  quantities  of  water 
are  also  often  stored  in  excavated  reservoirs  of  such  capacity  that  they 
may  be  called  storage-reservoirs.  They  are  similar  in  construction  to 
the  smaller  service  or  distributing  reservoirs  and  will  be  discussed  in 
Chapter  XXVII.  They  are  seldom  used  for  impounding  the  flow  of 
small  streams,  but  rather  for  purposes  such  as  sedimentation,  storage 
of  river-water  to  avoid  the  necessity  of  pumping  during  the  floods, 
storage  of  ground-water  to  allow  of  more  uniform  operation  of  wells, 
etc.* 

Natural  lakes  or  ponds  can  frequently  be  utilized  as  reservoirs. 
Their  value  for  storage  will  depend  upon  the  amount  their  surfaces  can 
be  varied  in  elevation,  and  not  upon  their  total  capacity. 

*  It  has  been  proposed  to  construct  storage-reservoirs  of  this  nature  on  the 
Thames  watershed  for  the  London  water-supply,  there  being  few  or  no  good  natural 
reservoir-sites. 

327 


328  IMPOUNDING  RESERVOIRS. 

363.  Factors  to  be  Considered. — In  all  questions  of  storage  there  are 
three  general  factors  to  be  considered:   (i)  the  yield  of  the  source  for 
successive  intervals  of  time;   (2)  the  demand  for  all  purposes  for  like 
intervals   of  time;  and    (3)   the   storage   necessary  or  available.      The 
problem  may  be  to  determine  the  storage  necessary  with  the  first  two 
factors  given,  or  it  may  be  to  determine  the  maximum  possible  demand 
from  a  given  watershed  when   the  amount  of  storage   is  limited,  or  it 
may   be   to   determine   the   supplying   capacity    of  the   watershed   for 
various  volumes  of  storage  when  comparing  the  cost  of  different  sources 
of  water-supply. 

The  yield  of  the  source  of  supply  has  been  discussed  in  Chapter  VI. 
The  demand  to  be  considered  includes  not  only  the  consumption  for 
the  city  in  question,  but  also  the  loss  of  water  by  evaporation  from 
water-surfaces  not  included  in  the  estimate  of  the  flow  of  the  stream, 
such  as  that  from  the  area  of  the  reservoir  itself,  also  loss  from  leakage 
and  percolation,  and  often  the  necessary  withdrawals  to  satisfy  the 
demands  of  riparian  owners  below.  The  reservoir  surface  may  be 
taken  at  from  3  to  5  per  cent  of  the  total  area,  but  if  the  assumed  area 
is  found  later  to  be  materially  in  error,  the  computations  may  be 
revised.  The  amount  of  leakage  through  the  dam  will  usually  be  very 
small,  but  with  certain  forms  of  construction  may  be  large.  This 
question  is  further  discussed  in  succeeding  chapters. 

The  ultimate  loss  by  percolation  will  not  be  large  unless  the  dam 
is  underlain  by  a  porous  stratum  which  will  lead  the  water  away 
underneath.  A  careful  geological  examination  of  the  impounding  area 
and  of  the  cross-section  at  the  site  of  the  dam  will  determine  this  point. 
If  porous  earth  overlies  impervious  strata,  the  ground-water  flow  may 
be  made  use  of  to  increase  the  capacity  of  the  stream;  and,  further- 
more, as  a  reservoir  fills,  such  porous  material  will  become  fully 
saturated  and  will  act  to  increase  the  capacity  of  the  given  reservoir 
beyond  its  apparent  capacity.  As  this  increase  due  to  ground-water 
is  difficult  to  estimate,  it  should  be  considered  as  an  additional  safeguard 
and  not  relied  upon  except  under  very  favorable  circumstances.  Cases 
have  been  cited  where  the  capacity  has  thus  been  increased  20  to  30 
per  cent. 

A  fourth  factor  to  be  considered  is  that  of  the  effect  of  storage  upon 
the  quality  of  the  water;  and  it  may  be  desirable  for  the  sake  of  the 
improvement  resulting  from  storage  to  make  the  capacity  greater  than 
that  determined  from  considerations  of  quantity  alone. 

364.  Appropriation  of  Surface-waters. — The  quantity  of  water  neces- 
sary to  satisfy  the  demands  of  the  riparian  owners  below  the  reservoir 


CAPACITY  OF  RESERVOIRS.  329 

is  often  an  exceedingly  difficult  matter  to  determine,  and  usually 
becomes  a  question  for  the  courts  to  settle.  Practice  differs  greatly  in 
different  States,  and  in  many  of  the  Western  States  the  water  belongs 
to  the  State  to  dispose  of  as  it  sees  fit.  It  is  often  expedient  to  buy  up 
all  rights  and  to  utilize  whenever  necessary  the  entire  flow  of  a  stream, 
or  to  fix  by  contract  the  amount  which  will  be  allowed  to  flow.  When 
full  water  compensation  is  given  the  amount  is  determined  on  the 
general  principle  that  only  that  portion  of  the  flow  can  be  abstracted 
that  is  not  ordinarily  used  by  the  riparian  owners  for  legitimate  pur- 
poses, such  as  for  water-power,  domestic  uses,  etc.  This  would 
usually  mean  that  during  the  dry  months  all  of  the  natural  flow  must 
be  allowed  to  pass,  and  during  the  remainder  of  the  year  a  uniform 
quantity  equal  in  value  for  the  uses  in  question  to  the  former  flow  of 
the  stream.  The  amount  in  any  case  would  thus  depend  much  on 
local  circumstances.  Many  court  decisions  in  this  country  have 
awarded  damages  for  diverting  flood-waters  that  were  entirely  use- 
less to  the  riparian  owners.  In  England  a  volume  equal  to  one- 
third  the  total  flow  has  often  been  adopted  as  compensation.  In  any 
case  the  most  of  the  flood-flow  would  be  available,  and  this  usually 
amounts  to  considerably  more  than  half  the  total  flow. 

365.  Computation  of  Storage. — The  method  of  computation  described 
below  is  essentially  that  of  Rippl.*  It  consists  in  graphically  repre- 
senting the  net  yield  of  the  source  in  question  during  dry  periods,  and 
in  obtaining  from  the  resulting  curve  the  solutions  to  the  various  forms 
of  the  problem  which  may  be  presented. 

The  method  is  as  follows:  From  the  measured  or  estimated  flow  of 
the  stream  for  each  month  during  the  period  to  be  treated,  subtract 
the  monthly  loss  by  evaporation  from  water-surfaces  not  included  in 
the  estimate,  the  monthly  loss  by  leakage,  and  the  monthly  compen- 
sation as  previously  determined.  The  result  will  be  the  net  yield  for 
each  month.  Add  together  the  yields  from  the  beginning  to  each 
month  in  succession;  then  from  these  figures  construct  a  curve  OA, 
Fig.  66,  in  which  the  abscissa  of  any  point  is  the  total  time  from  the 
beginning  of  the  selected  period,  and  the  ordinate  is  the  total  net  flow 
during  the  time  represented  by  the  abscissa.  The  inclination  of  the 
curve  at  any  point  is  thus  equal  to  the  rate  of  the  net  flow,  a  minus 
inclination,  as  at  B,  representing  a  negative  flow.  Now  in  like  manner 
plot  a  curve  of  consumption,  OC,  which  may  ordinarily  be  assumed  as 
a  straight  line,  as  the  variation  month  by  month  is  a  refinement  hardly 
warranted  by  the  accuracy  of  the  other  data. 

*  Proc.  Inst.  C.  E.,  LXXI.  p.  270. 


330 


IMPO  UNDING-RESER  VO1RS. 


The  ordinates  between  the  lines  OA  and  OC  will  now  represent 
the  total  surplus  from  the  beginning,  and  where  the  two  lines  con- 
verge, as  at  B  and  D,  the  yield  is  less  than  the  demand,  and  con- 
versely. The  greatest  deficiency  occurring  during  any  dry  period  B 
is  found  by  drawing  EF  parallel  to  OC  and  tangent  to  the  curve;  and 
the  amount  of  it  is  given  by  the  maximum  ordinate  IG  drawn  from  EF  to 


FIG.  66. 

the  curve.  The  deficiency  for  any  other  dry  period  is  likewise  found, 
and  the  maximum  so  found  is  the  storage  volume  required  to  supply 
the  demand  OC.  The  time  during  which  the  reservoir  would  be  drawn 
down  below  high-water  line  would  be  represented  by  the  horizontal 
distance  between  E  and  the  point  of  intersection  F.  In  like  manner 
the  storage  capacity  for  any  other  rate,  OC'j  may  be  determined  by 
measuring  from  the  tangent  EF' . 

If  the  tangent  from  any  summit  does  not  intersect  the  curve,  it  indi- 
cates that  during  the  period  investigated  the  supply  is  not  equal  to  the 
demand ;  and  to  insure  a  full  reservoir  at  the  point  E,  for  example,  it 
is  necessary  for  the  parallel  tangent  drawn  backwards  from  G  to  inter- 
sect the  curve  at  some  point  H.  In  investigating  various  dry  periods 
it  is  therefore  necessary  to  begin  the  curve  a  year  or  two  back  of  the 
dry  years  to  insure  the  accumulation  of  surplus  water.  When  actual 
stream  measurements  are  to  be  had  covering  a  series  of  years,  it  is  best 
to  consider  the  entire  period. 

If  the  yield  is  to  be  limited  by  the  time  during  which  the  reservoir 
is  to  be  drawn  below  high-water  line,  the  rate  of  supply  and  corre- 


CAPACITY   OF  RESERVOIRS.  331 

spending  storage  can  be  determined  by  finding  by  trial  the  line  of 
lowest  slope  which  shall  be  tangent  at  a  summit,  and  whose  horizontal 
projection  equals  the  time  specified.  If  the  storage  is  fixed  and  it  is 
desirable  to  know  what  amount  of  water  the  area  will  yield  at  a  con- 
stant rate  per  month,  the  rate  is  found  by 
drawing  the  lines  EF  from  various  summits, 
which  shall  have  their  maximum  ordinates, 
GI,  equal  to  the  given  storage.  The  rate 
is  given  by  the  line  of  least  slope. 

If  the  case  is  one  where  the  consump- 
tion cannot  be  assumed  as  uniform,  the  line 
OC  will  be  a  curve,  and  the  desired  infor- 
mation can  be  more  easily  got  by  replotting  the  ordinates  between  the 
demand   and  supply  curves — the  accumulated   surplus — from  a  hori- 
zontal axis,  as  in  Fig.  67.      Storage  volumes,  etc.,  are  then  found  by 
drawing  the  tangent  lines  EF,  etc. ,  horizontally. 

366.  Storage  Calculation  from  the  Sudbury  River  Records. — The 
results  of  calculations  of  storage  volumes  based  on  the  records  of  the 
flow  of  the  Sudbury  River  watershed  are  given  in  Table  No.  58.  The 
data  are  from  a  more  extended  table  by  Mr.  FitzGerald.*  The  Sud- 
bury watershed  has  3^  per  cent  of  water-surface,  and  the  observed  flow 
is  reduced  to  monthly  flow  from  one  square  mile  of  land-surface  by 
correcting  for  evaporation  from  the  water-surface.  Then  from  these 
figures,  and  the  yield  from  one  square  mile  of  water-surface  as  given 
by  the  difference  between  rainfall  and  evaporation,  calculations  are 
made  of  the  yield  of  one  square  mile  having  various  percentages  of 
water-surface.  These  results  are  then  plotted  and  the  storage  volumes 
for  various  rates  of  consumption  determined  in  a  way  similar  to  that 
explained  in  the  preceding  article.  Mr.  FitzGerald  estimated  the 
evaporation  for  each  month  throughout  the  entire  period,  but  nearly 
the  same  results  would  be  obtained  by  using  the  mean  monthly 
evaporations  as  given  on  page  56. 

Table  No.  17,  page  84,  gives  the  data  of  stream-flow  covering  the 
most  important  part  of  the  record,  and  from  these  figures  and  the  mean 
monthly  evaporations  the  student  should  be  able  to  obtain  storage 
volumes  closely  agreeing  with  those  of  the  table  up  to  a  daily  draught 
of  600,000  to  800,000  gallons,  depending  upon  the  percentage  of 
water-surface.  Beyond  this  the  draught  is  greater  than  the  average 
flow  for  the  five  years  given,  and  a  longer  period  would  need  to  be 
considered. 

*  Trans.  Am.  Soc.  C.  E.,  1892,  xxvu.  pp.  267,  268. 


332 


IMPO  UNDING-RESER  VOIRS. 
TABLE   NO.    58. 


STORAGE  CAPACITY  REQUIRED  FOR  VARIOUS  DAILY  DRAFTS  FROM  ONE  SQUARE  MILE 
OF  WATERSHED  CONTAINING  VARIOUS  PERCENTAGES  OF  WATER-SURFACE  BASED  ON 
SUDBURY  RIVER  RECORDS. 


o  per  cent. 

10  per  cent. 

25  per  cent. 

Constant 
Daily  Draft. 

Storage 
Volume 
per  Sq.  Mile. 

Length  of 
Time  Reser- 
voir is  Below 
High-  water. 

Storage 
Volume 
per  Sq.  Mile. 

Length  of 
Time  Reser- 
voir is  Below 
High-water. 

Storage 
Volume 
per  Sq.  Mile. 

Length  of 
Time  Reser- 
voir is  Beiotf 
High-water. 

Gallons. 

Gallons. 

Months. 

Gallons. 

Months. 

Gallons. 

Months. 

100,000 
150,000 

314,000 
3,006,000 

3* 

I5,OI2,OOO 
19,642,000 

3 

53,565,000 
59.665,000 

8 

_ 

2OO,OOO 

8,797,000 

7* 

25,742,000 

7: 

r 

65,765,000 

8, 

25O,OOO 

17,997,000 

7* 

33,338,000 

8. 

71,865,000 

8 

! 

300,000 

28,473,000 

8£ 

43,437,000 

8f 

78,807,000 

Bi 

i 

350,000 

39,173,000 

9^ 

54,137,000 

9F 

87,957,000 

9 

t 

400,000 

51,303,000 

9* 

66,050,000 

99,089,000 

ioi 

450,000 

63,553,000 

9* 

78,300,000 

IO 

r 

127,412,000 

«I 

5OO,OOO 

75,803,000 

9^ 

90,550,000 

IO 

. 
| 

156,362,000 

21 

r 

550.000 

88,053,000 

9* 

105,987,000 

21 

185,312,000 

22 

r 

6oo,OOO 

100,65  1,000 

10* 

134,937,000 

21 

214  262,000 

22 

650,000 

114,451,000 

10* 

163,887.000 

21 

250,744,000 

92 

700,000 

139,950,000 

21^ 

192  837,000 

22 

336,044,000 

1  06 

750,000 

168,900,000 

2l| 

221,787,000 

23: 

421,344,000 

115 

800,000 

199,106,000 

58? 

297,460,000 

r 

506,644,000 

125 

850,000 

250,328,000 

80| 

380,557,000 

f 

591,944,000 

141 

qoo,000 

334,078,000 

93* 

465,857,000 

116 

677,244,000 

I65* 

*  Estimated. 

This  table  of  storage  volumes  is  considered  a  safe  one  to  use  for 
streams  in  New  England.  A  similar  table  can  be  constructed  for  any 
locality  where  accurate  data  are  at  hand,  and  in  such  form  the  informa- 
tion can  readily  be  used  in  estimating  yields  and  storage  volumes  for 
other  areas  in  the  vicinity  and  for  various  parts  of  the  same  watershed. 

As  an  example  of  the  use  of  the  table  let  it  be  required  to  determine 
the  necessary  storage-capacity  to  supply  a  constant  daily  draught  of 
7  million  gallons  from  a  watershed  of  12  square  miles  having  10  per 
cent  of  water-surface.  The  draught  from  one  square  mile  will  be  equal 
to  583,000  gallons,  and  by  interpolation  the  reservoir  capacity  is  about 
125  million  gallons  per  square  mile,  or  a  total  capacity  of  1500  million 
gallons.  It  will  be  below  high  water  for  a  period  of  I  year  9^ 
months. 

367.  Capacity  of  a  System  of  Reservoirs. — If  there  are  several 
reservoirs  on  the  same  watershed,  the  supplying  capacity  of  any  com- 
bination may  be  found  by  the  use  of  the  methods  just  described. 
Beginning  with  the  reservoir  farthest  up  the  valley,  the  net  flow  is 
determined  and  plotted,  from  which  the  maximum  possible  average 


LOCATION  AND    CONSTRUCTION.  333 

draught  is  found.  Whenever  the  supply  exceeds  this  draught  with 
full  reservoir  the  excess  passes  to  the  next  reservoir  below  and  adds 
to  the  supply  from  its  own  tributary  area.  Its  supply  curve  can  now 
be  drawn  and  capacity  determined,  and  so  on. 

LOCATION   AND   CONSTRUCTION. 

368.  Considerations  Affecting  Location. — The  proper  location  of  an 
impounding-reservoir  requires  the  consideration  of  many  elements. 
In  the  first  place  the  location  determines  the  size  of  the  tributary 
watershed,  and,  as  the  capacity  is  directly  dependent  upon  the  size 
of  the  watershed,  different  locations  will  call  for  different  capacities 
to  furnish  like  quantities  of  water. 

The  location  is  also  very  largely  determined  by  the  distance  of  the 
reservoir  from,  and  elevation  above,  the  point  of  distribution.  Long 
distances  require  heavy  expenditures  for  conduits  or  pipe-lines,  but 
these  expenditures  are  relatively  less  the  larger  the  quantity  of  water 
dealt  with.  For  large  cities  it  will  therefore  be  practicable  to  go  much 
farther  for  water  than  for  small  cities.  Regarding  the  elevation  of  the 
reservoir  it  is  very  desirable  that  it  shall  be  sufficient  to  enable  all  or  a 
part  of  the  consumers  to  be  served  by  gravity  alone,  and  it  will  be 
economy  to  spend  a  relatively  large  sum  of  money  for  conduits  or 
otherwise  to  secure  this  advantage.  The  necessary  elevation  for  this 
purpose  depends  upon  the  required  pressure  at  and  elevation  of  the 
various  points  of  distribution,  and  the  head  lost  in  conducting  thence 
the  water.  These  features  are  discussed  subsequently  and  as  separate 
problems,  but  in  the  actual  case  they  are  all  interdependent  and  must 
be  considered  together.  Distant  locations  at  high  elevations  will  often 
need  to  be  compared  in  economy  with  near  locations  requiring  the  use 
of  pumps. 

The  question  of  future  extension  is  an  important  one,  especially  in 
large  works,  and  the  selection  of  a  certain  watershed  for  a  supply  may 
be  determined  not  so  much  by  the  location  of  a  single  reservoir  as  by 
the  existence  of  sites  for  several  reservoirs  in  order  that  the  capacity 
of  the  watershed  may  in  time  be  developed  to  its  fullest  extent  as  the 
demand  for  water  increases.* 

In  questions  pertaining  to  cost  the  economy  of  a  reservoir  alone  is 

*For  important  examples  see  Report  Mass.  Board  of  Health  upon  a  Metropolitan 
Water-supply,  1895  ;  Wegmann,  The  Water-supply  of  New  York,  1896  ;  Report  upon 
Future  Extension  of  the  Water-supply  of  Brooklyn,  1896  ;  Freeman's  Report  on 
New  York's  Water-supply,  1900. 


334  IMPOUND  ING-RESERVOIRS 

measured  by  the  cost  per  million  gallons  stored,  but  a  more  significant 
quantity  is  the  cost  per  million  gallons  of  daily  supplying  capacity  of 
reservoir  and  watershed ;  or  in  case  the  reservoir  is  one  of  a  system, 
the  cost  per  million  gallons  supplying  capacity  added  by  the  reservoir 
in  question. 

369.  Topographic  and  Geologic  Features. — The  most  favorable  lo- 
cation for  a  reservoir  as  regards  topography  is  a  point  where  the  valley 
forms  a  comparatively  broad  level  area  bounded  by  steep  slopes  at  the 
sides,  and  below  which  the  hills  approach  close  together  so  as  to  form 
a  good  site  for  a  dam.      Such  an  ideal  site  is  rarely  found,  and  it  will 
usually  be  necessary  to  compare  two  or  more  possible  sites,  for  which 
purpose  careful  estimates  of  cost  will  be  required.     A  site  which  will 
include   much    swampy  area  or  involve   a   large  amount  of  shallow 
flowage  is  objectionable  on  -the  grounds  of  quality. 

To  prevent  the  escape  of  water  the  floor  of  the  reservoir  should 
contain  no  outcrop  of  porous  strata  of  any  extent  which  may  lead  the 
water  away  underground,  and  in  the  vicinity  of  the  dam  or  embank- 
ment it  should  be  underlain  by  an  impervious  stratum  at  a  depth  that 
can  be  reached  by  that  structure.  In  some  cases  these  conditions 
cannot  be  secured  and  some  loss  through  porous  ground  must  be 
expected. 

Besides  the  character  of  the  substrata  in  the  vicinity  of  the  dam, 
the  kind  of  soil,  proximity  of  suitable  stone  for  a  masonry  dam  or  of 
material  for  an  earth  embankment,  are  questions  controlling  to  a  large 
extent  the  location  of  a  reservoir. 

370.  Surveys  and  Preliminary  Work. — To  make  even  a  preliminary 
determination    of  reservoir-site    in     accordance    with    the    preceding 
principles  requires  a  fairly  accurate  knowledge  of  the  areas  of  various 
portions   of  the  watersheds   and   of  their   relative  elevations.      If  this 
information  cannot  be  obtained  from  existing  maps,  a  reconnoissance 
survey  must  be  made.      For  this  purpose  the  transit  and  stadia  method 
is  well  adapted. 

After  a  tentative  location  has  been  decided  upon,  accurate  levels 
must  be  run  to  connect  the  town  with  the  reservoir-site,  also  surveys 
for  conduit  lines,  and  an  accurate  topographical  survey  of  the  area  to 
be  flooded  and  all  that  may  be  affected  by  the  reservoir.  This  survey 
should  include  information  as  to  all  buildings  upon  and  adjacent  to  the 
area  in  question,  nature  of  the  vegetation,  location  of  roads,  property 
lines,  etc.  In  addition  to  this  it  will  prove  of  much  subsequent  value 
to  have  a  topographical  survey  made  of  the  entire  watershed,  which 
may  be  less  accurate  than  that  for  the  reservoir.  At  the  same  time  a 


LOCATION-  AND    CONSTRUCTION.  335 

complete  sanitary  survey  of  the  watershed  can  be  made,  as  outlined  in 
Chapter  VIII,  Art.  154,  and  a  good  topographical  map  will  prove  of 
great  convenience  in  this  connection. 

Determinations  should  be  made  of  the  character  of  the  soil,  amount 
of  organic  matter  at  various  depths,  especially  in  swamps  or  old  ponds, 
and  nature  of  substrata  with  reference  to  its  permeability.  At  the  site 
proposed  for  the  dam  numerous  borings  must  be  made  extending  to  a 
considerable  distance  above  and  below  the  dam  as  well  as  on  the 
flanks,  and  these  must  be  supplemented  by  test-pits  so  that  the  nature 
of  the  supposed  firm  stratum  can  be  accurately  determined.  If  a  suitable 
foundation  cannot  be  reached  at  a  reasonable  cost,  the  site  may  have 
to  be  abandoned. 

371.  Depth  of  Reservoir. — Calculations  of  storage  volumes  for  differ- 
ent depths  can  readily  be  made  from  the  contour  map.  The  areas 
enclosed  by  each  contour  can  be  measured  by  a  planimeter  and  the 
volume  between  any  two  successive  contours  taken  as  equal  to  the 
average  of  the  areas  enclosed  by  the  contours,  multiplied  by  the  con- 
tour interval.  Where  the  slopes  are  very  flat  this  method  gives  an 
appreciable  error,  and  in  that  case  it  may  be  advisable  to  employ  the 
prismoidal  formula.  By  this  formula,  the  volume  of  two  successive  slices 
in  terms  of  the  three  areas  a,  b,  and  c  (the  two  end  and  the  intermediate 

areas)  is  equal  to  (a  -f-  4&  +  0~~»  where  d  is  the  contour  interval.     The 

volume  up  to  any  given  contour  having  been  determined,  the  necessary 
height  of  dam  to  hold  any  given  quantity  of  water  becomes  known. 

From  considerations  of  quality,  it  should  never  become  necessary 
to  withdraw  the  water  to  the  very  bottom  of  a  reservoir,  so  that  the 
volume  for  a  few  feet  in  depth  at  the  bottom  should  be  omitted  from 
the  calculations.  What  this  depth  should  be  depends  upon  the  char- 
acter of  the  water  and  the  shape  of  the  basin.  It  may  be  taken,  with 
very  little  loss  of  capacity,  at  one -fifth  or  even  one-fourth  the  total 
height  of  the  dam.  With  sediment-bearing  streams  some  allowance 
should  be  made  for  the  silting  up  of  the  reservoir,  the  amount  of  which 
can  be  estimated  from  analyses  of  the  water.  In  the  case  of  some 
streams  this  is  a  matter  of  importance  and  may  involve  considerable 
expense  for  the  removal  of  the  sediment  from  time  to  time. 

A  noteworthy  case  of  the  rapid  silting  up  of  a  reservoir  is  that  of 
the  reservoir  formed  by  the  dam  across  the  Colorado  River  at  Austin, 
Texas.  This  dam  was  completed  in  1893,  and  at  that  time  formed  a 
reservoir  of  a  capacity  of  17,000  million  gallons,  whereas  in  February, 
1900,  the  capacity  had  become  reduced  to  8600  million,  or  only  52  per 


336  IMPOUND  ING-RESERVOIRS. 

cent  of  the  original  amount.  The  cause  of  this  large  amount  of  deposit 
was  the  very  large  discharge  of  a  silt-bearing  stream  as  compared  to 
the  capacity  of  the  reservoir.* 

Where  the  volume  is  not  fixed,  as  in  the  case  of  a  series  of  reser- 
voirs, the  economical  height  is  determined  by  comparative  estimates  of 
cost  for  various  volumes.  Such  estimates  must  of  course  include 
expense  for  land,  water  rights,  etc.,  as  well  as  for  the  constructive 
features. 

372.  Cleaning  the  Site. — In  Chapter  IX  the  injurious  effect  upon  the 
quality  of  the  water  of  organic  matter  in  reservoirs  was  discussed,  and 
the  necessity  for  the  removal  of  all  vegetation  and  perishable  matter 
from  the  reservoir-site  was  pointed  out.  Still  further  it  has  been  shown 
to  be  desirable  and  of  great  benefit  to  the  water  to  remove  the  top  soil 
to  a  sufficient  depth  to  include  most  of  the  organic  matter  therein. 
Such  stripping  has  for  some  years  been  done  for  some  of  the  large 
reservoirs  of  the  Boston  Water-works  and  at  other  places,  especially  in 
Massachusetts,  with  the  result  that  the  impounded  water  from  the  first 
has  suffered  no  deterioration  by  storage.  In  other  reservoirs  where 
this  has  not  been  done,  trouble  has  been  experienced  for  many  years. 
Where  the  deposit  of  organic  matter  is  very  deep,  and  the  expense 
of  removing  too  great,  a  covering  of  gravel  is  advisable. 

In  investigating  the  soil  from  the  site  of  the  proposed  Nashua 
reservoir,  Dr.  T.  M.  Drown  of  the  Mass.  Board  of  Health  found  that 
the  amount  of  organic  matter  in  a  soil  decreases  rapidly  with  the  depth. 
The  percentage  at  the  surface  was  usually  8  per  cent  or  more,  while 
at  10  or  12  inches  below  there  was  usually  but  i^  to  2  per  cent.  As 
a  result  of  this  study  he  suggests  these  lower  figures  as  a  provisional 
standard  for  the  permissible  percentage  of  organic  matter  which  may 
be  allowed  to  remain. f 

As  an  example  of  soil-stripping  on  a  large  scale  mention  may  be 
made  of  the  work  done  on  Reservoir  No.  5  of  the  Boston  Water-works.  J 
The  soil  was  in  general  removed  to  a  depth  of  about  i  foot,  but  in 
places  to  a  much  greater  depth.  In  one  pocket  of  mud  20  feet  deep 
the  amount  of  organic  matter  at  the  surface  was  75  per  cent,  and  at  10 
feet  deep,  the  depth  of  the  excavation,  it  was  5  per  cent.  The  total 
amount  removed  in  this  way  was  about  4  million  cubic  yards,  adding 
in  this  way  about  10  per  cent  to  the  capacity  of  the  reservoir.  In  the 
proposed  Nashua  reservoir  the  cost  of  such  removal  is  estimated  at 
nearly  $3,000,000. 

*  Eng.  News,  1900,  XLIII.  p.  135. 

f  Report  Mass.  Board  of  Health,  1893,  p.  383. 

I  Eng.  News,  1897,  xxvii.  p.  130. 


MAINTENANCE   OF  RESERVOIRS.  337 

373,  Shallow  Flowage. — As  a  further  protection  to  the  quality  of 
stored  water   it  is   desirable  that    there  be   as   little   area   alternately 
flooded  and  exposed  as  possible,  in  order  to  limit  the  growth  of  vege- 
tation.     Here  again  the  practice  of  the  Boston  Water  Board  is  to  be 
recommended.      The  minimum  depth  at  high  water  allowed  in  Reser- 
voir No.  5  is  8  feet.      Shallow  places  are  either  excavated  to  this  depth 
below  high- water  line,  or  are  partly  excavated  and  partly  filled,  the 
slopes  being  formed  at  3  to  I  and  covered  with  2  feet  of  gravel. 

374.  Maintenance. — In  maintaining  a  reservoir  so  as  to  preserve  the 
quality  of  the  water  and  to  supply  the  necessary  quantity  regularly  and 
certainly  requires  a  considerable  degree  of  care   and   attention.      To 
keep  the  quality  as  good  as  possible  requires  first  of  all  that  the  water- 
shed and  reservoir  be  kept  free  from  organic  pollution.      To  insure  that 
this  is  the  case  the  city  should  have  sanitary  supervision  over  the  area 
in  question,  and  inspection  should  be  regularly  made  to  see  that  all 
sanitary  requirements  are  complied  with.* 

In  addition  to  the  prevention  of  pollution  from  animal  sources  it  is 
desirable  that  the  reservoir  be  kept  as  free  as  possible  from  vegetation. 
During  seasons  of  low  water,  opportunity  is  offered  for  removing  the 
vegetation  from  around  the  borders  of  the  reservoir.  Where  there  is 
more  or  less  unavoidable  organic  matter  present  in  the  water  there  will 
at  times  be  objectionable  tastes  and  odors  at  certain  depths.  To 
obtain  the  best  water  available  the  depth  at  which  it  is  drawn  from  the 
reservoir  should  be  varied  from  time  to  time  according  to  the  condition 
of  the  water.  Frequent  analyses  of  water  drawn  from  different  depths 
are  very  valuable  in  this  connection. 

t^VVhen  reservoirs  ha^ve  become  silted  up  to  a  considerable  extent  it 
may  be  necessary  to  remove  the  deposit.  If  the  dam  be  located  in  a 
narrow  valley,  much  can  be  removed  by  flushing  through  sluice-gates. 
The  greater  part  of  the  material  will,  however,  have  to  be  taken  out  by 
methods  similar  to  those  used  in  ordinary  excavations.  In  case  the 
silt  brought  down  contains  much  organic  matter  it  should  be  removed 
frequently  in  order  to  prevent  trouble  from  its  decay. 

Careful  records  should  be  kept  at  the  reservoir  of  all  matters  which 
may  be  of  any  value  in  subsequent  designs  for  enlargement  or  for  new 
works.  These  should  include  records  of  rainfall,  temperature,  height 
of  water  in  reservoir,  amount  passing  over  waste-weir,  and  data  per- 
taining to  the  quality  of  the  water  at  different  seasons  of  the  year. 

The  maintenance  of  dams  and  embankments  should  call  for  very 

*For  details  of  methods  of  making  such  inspection  and  the  requirements  which 
have  been  imposed  in  certain  instances  see  Reports  N.  Y.  State  Board  of  Health, 
1889,  1894.  See  also  Literature  of  Chap.  VIII. 


IMPOUND  ING-RESERVOIRS. 

little  labor.  Earthen  embankments  should  be  kept  neat  in  appearance 
with  slopes  well  sodded,  or  covered  with  large  gravel  so  as  to  be  per- 
manent. The  top  of  the  embankment  should  of  course  be  maintained 
at  its  full  height,  and  the  waste-weir  and  the  channel  below  it  kept 
clear  and  of  the  designed  capacity  at  all  times.  Gates  and  other 
apparatus  should  be  frequently  inspected  and  kept  in  thorough  repair. 
Flashboards  should  be  used  with  great  caution,  if  at  all.  They  should 
always  be  so  designed  that  they  will  fall  or  be  washed  away  when  the 
water  begins  to  flow  over  them.  Immediate  attention  should  be  given 
to  any  sign  of  increased  leakage  in  the  case  of  either  an  earthen  or  a 
masonry  dam.  Leaks  or  excessive  seepage  in  masonry  dams  may  be 
often  stopped  by  plastering  the  up-stream  face  of  the  dam  with  rich 
cement  mortar.  1  Any  visible  cracks  may  also  be  filled  with  Portland- 
cement  grout  "forced  in  under  pressure.  Earthen  dams  are  repaired 
with  difficulty.  If  the  seepage-water  flows  perfectly  clear,  the  indica- 
tions are  that  no  material  is  being  carried  away  and  that  there  is  no 
immediate  danger  of  the  leak  enlarging.  If  the  seepage-water,  on  the 
other  hand,  be  muddy  and  continue  so,  the  water  should  be  drawn  off 
at  once  and  the  dam  repaired.  This  may  sometimes  be  accomplished 
by  excavating  to  a  moderate  depth  at  the  upper  end  of  the  leak  and 
filling  with  puddle  well  rammed  into  place.  If  the  leak  is  a  serious 
one,  it  will  probably  be  necessary  to  cut  down  from  the  top  and  fill  with 
good  material  well  bonded  into  the  old  part  of  the  work,  and  compacted 
in  the  same  manner  as  for  a  new  embankment. 

LITERATURE. 

1.  Rippl.     The  Capacity  of  Storage-reservoirs  for  Water-supply.     Proc.  Inst. 

C.  E.,  1882-83,  LXXI.  p.  270. 

2.  Stearns.     The  Selection  of  Sources  of  Water-supply.     Jour.   Assn.   Eng. 

Soc.,  1891,  x.  p.  485. 

3.  FitzGerald,     Rainfall,  Flow  of  Streams,  and  Storage.     Trans.   Am.  Soc. 

C.  E.,  1892,  xxvn.  p.  304. 

4.  Drown.      On  the  Amount  and  Character  of  Organic  Matter  in  Soils  and  its 

Bearing  on  the  Storage  of  Water  in  Reservoirs.     Mass.  Bd.  Health 
Report,   1893,  p.  383. 

5.  Greenleaf.     A  Method  for  determining  the  Supply  from  a  Given  Water= 

shed.     Eng.  News,  1895,  xxxin.  p.  238. 

6.  Horton.     A  Form  of  Mass  Diagram  for  Studying  the  Yield  of  Watersheds. 

Eng.  Record,  1897,  xxxvi.  p.  285. 

7.  Saville.     Clearing  and  Enlarging  the  Spot-Pond  Storage  Reservoir,  Met- 

ropolitan Water-supply.     Eng.  News,  1901,  XLVI.  p.  442. 

8.  Larned.     The  Drainage  of  Swamps  for   Watershed  Improvement.    Jour. 

New  Eng.  W.  W.  Assn.,  1902,  xvi.  p.  36. 

9.  Spooner.     Haskell's  Brook  Reservoir  and  Dam,  Gloucester,  Mass.     Jour. 

New  Eng.  W.  W.  Assn.,  March,  1905. 


CHAPTER   XVI. 

EARTHEN   DAMS. 

GENERAL   CONSIDERATIONS. 

375.  The  Requisites  of  a  Dam. — The  function  of  a  dam  is  to  prevent 
the  passage  of  water.     To  this  end  it  must  be  impervious,  or  sufficiently 
so  to  prevent  excessive  loss  of  water;  and  it  must  be  stable.     The 
possible  consequences  of  a  defect  in  the  latter  requirement  are  exceed- 
ingly serious,  as  has  been  demonstrated  by  the  great  loss  of  life  and 
property  caused  by  the  failure  of  reservoir  embankments  in  the  past. 

These  two  properties,  imperviousness  and  stability,  may  or  may 
not  be  independent  of  each  other,  according  to  the  nature  of  the  con- 
struction ;  but  it  will  in  any  case  be  of  advantage  to  consider  them  as 
distinct  and  separate.  In  other  words,  a  dam  must  have  an  impervious 
body,  and  this  must  be  safely  supported. 

376.  Kinds  of  Dams. — Dams    may   be    divided    according   to    the 
material  used  into  five  classes:  earthen  dams,  masonry  dams,  loose-rock 
dams,  wooden  dams,  and  iron  or  steel  dams.     These  materials  are  also 
used  in  various  combinations.      The  form  of  dam  suitable  for  a  given 
case  depends  upon  the  character  of  the  foundation,  the  topography  of 
the  site,  the  size  and  importance  of  the  structure,  the  degree  of  imper- 
viousness required,  and  the  cost.      Of  the  above  kinds  of  dams  those 
of  masonry  and  of  earth  are  the  ones  usually  considered  and  will  here 
be  fully  treated.      The  other  forms  will  be   treated   as  fully  as  their 
importance  seems  to  warrant. 

377.  The  Dam  as  a  Porous  Structure.  — Before  proceeding  with  the 
discussion  of  the  various  forms  it  will  be  well  to  consider  the  action  of 
the  dam  as  a  porous  structure.      Few  dams  are  absolutely  impervious 
and  many  are  far  from  it,  yet  they  may  do  good  duty  as  impounders  of 
water ;  but  whether  a  dam  is  impervious  or  not  is  a  matter  that  in  most 
cases  greatly  affects  the  stability  and  should  be  carefully  considered. 

Let  ABC,   Fig.  68,  be  a  body  of  porous  material  (whether  very 

339 


340  EARTHEN  DAMS. 

porous,  as  sand  or  loose  rock,  or  only  slightly  so,  as  most  masonry 
dams,  is  for  the  present  immaterial),  resting  upon  a  porous  foundation 
and  retaining  water  at  the  level  D.  Under  the  assumed  conditions 

some  water  will  percolate  through 
and  under  the  dam  and  escape  at  C 
in  a  way  similar  to  the  flow  of 
ground-water.  The  surface  of  the 
percolating  water  will  be  some 
curve,  such  as  DEC,  the  slope  of 

which  at  any  point  measures  the  relative  resistance  to  flow.  The 
amount  of  water  percolating  varies  of  course  with  the  porosity,  but 
even  with  fine  sand  or  earth  it  will  be  very  small,  so  that  the  require- 
ment as  to  imperviousness  may  be  met  with  a  porous  material. 

The  requirements  for  stability  depend  somewhat  upon  the  nature  of 
the  material  employed.  If  a  rigid  material  is  used,  such  as  masonry, 
the  dam  must  be  so  proportioned  as  to  resist  sliding  upon  its  founda- 
tions, it  must  not  be  overturned,  and  it  must  not  be  ruptured  or  over- 
strained in  any  of  its  parts.  If  a  material  such  as  earth,  sand,  or  loose 
rock  be  used  the  foregoing  requirements  must  be  met  so  far  as  they  are 
applicable  to  such  materials,  and  in  addition  the  important  requirement 
that  percolation  must  be  controlled  in  such  a  manner  as  to  prevent  any  ma- 
terial being  carried  away  by  the  water.  The  effect  of  percolating  water 
upon  the  character  of  the  material  must  also  be  carefully  considered. 
As  the  stability  of  any  form  of  dam  is  largely  dependent  upon  the 
weight  of  the  material  it  is  important  to  inquire  what  effect  any  per- 
colating water  will  have  upon  this  factor. 

378.  The  Buoyant  Effect  of  Percolating  Water.  —  If  the  material 
consists  of  loose  grains  like  sand  or  earth,  the  loss  of  weight  for  the 
portion  submerged  is  equal  to  the  weight  of  the  water  displaced.  If  / 
is  the  ratio  of  porosity  by  volume,  the  volume  of  water  displaced  for 
each  cubic  foot  of  the  material  is  I  — /,  the  weight  of  which  is 
(i  —  p]  62.5  pounds.  Thus  with  a  porosity  of  40  per  cent  the  loss  in 
weight  of  sand,  weighing,  say,  100  pounds,  will  be  (i  —  .40)  62.5  =  37 
pounds  per  cubic  foot,  leaving  a  net  weight  of  63  pounds. 

If  the  material  is  cohesive  like  stone  or  cement,  the  water  cannot 
exert  an  upward  pressure  upon  the  entire  surface  of  any  horizontal  sec- 
tion, and  the  buoyant  effect  will  be  much  less  than  the  above.  Assum- 
ing that  the  full  effect  will  occur  whenever  the  porosity  is  as  great  as 
33i  Per  cent  (this  being  approximately  the  porosity  of  well-compacted 
sand),  and  that  with  a  cohesive  material  of  less  porosity  it  will  be  pro- 
portional to  the  porosity,  the  buoyant  effect  in  such  cases  will  be 


DEPTH  AND   AMOUNT  OF  PERCOLA  TING    WA  TER. 


341 


£-(\  — /)  62.5  =  3/(i  —  /)  62.5  pounds  per  cubic  foot ;  and  the  upward 

pressure  on  any  vertical  column  of  masonry  of  I  square  foot  in  cross- 
section  will  be  equal  to  3/  (i  — /)  62.5  xA  where  /z  =  distance  the 
column  is  submerged  below  the  water  surface  DEC  (Fig.  68).  Thus  in 
a  homogeneous  masonry  dam  having  a  porosity  of  5  per  cent,  the 
buoyant  effect  on  the  submerged  portion  will  be  approximately 
3  X  .05  (i  —  .05)62.5=  9  pounds  per  cubic  foot.  That  hydrostatic 
pressure  may  be  readily  transmitted  through  porous  stone  has  been  fully 
shown  by  experiments  and  would  in  any  case  hardly  admit  of  doubt.* 

The  following  table  gives  the  buoyant  effect  in  pounds  per  cubic 
foot  for  homogeneous  masonry  of  various  porosities,  calculated  in  accord- 
ance with  the  preceding  analysis. 


Porosity,  per  cent. 

Buoyant  Effect, 
Lbs.  per  cu.  ft. 

Porosity,  per  cent. 

Buoyant  Effect, 
Lbs.  per  cu.  ft. 

I 

1.9 

6 

10.6 

2 

3 

3-7 
5-5 

8 

12.  2 
I3.8 

4 

5 

7.2 
8.9 

9 

10 

15-3 

16.8 

In  a  structure  of  stone  having  a  small  porosity/,  with  mortar  joints 
of  large  porosity/',  the  buoyant  effect  at  the  joints  will  be  large  and  will 
be  equal  to  3//  (i  — /)  62.5  X  //.  If  any  loose  joint  exists,  or  any  place 
where  the  water  can  enter  in  "thin  sheets,"  then  p'  becomes  the  same 
as  assumed  for  loose  material,  namely,  33-^  per  cent,  and  the  buoyant 
effect  is  again  equal  to  (i  — /)  62.5  X  /^,  as  for  sand.  To  reduce  this 
effect  as  far  as  possible  in  masonry  it  is  thus  seen  to  be  necessary  to 
make  the  joints  of  as  little  porosity  as  the  stone  itself.  If  the  founda- 
tion be  more  porous  than  the  masonry,  and  open  to  the  percolation  of 
water,  the  maximum  buoyant  effect  will  be  at  the  bottom  and  measured 
by  the  porosity  of  the  foundation. 

379.  Influences  Affecting  the  Depth  and  Amount  of  Percolating 
Water. —  From  the  discussion  in  Chapter  VII  relative  to  the  flow  of 
ground-water  it  is  evident  that  the  quantity  of  water  percolating 
through  a  dam  depends  in  general  upon  the  thickness  of  the  dam  and 
the  fineness  of  the  material  of  which  it  is  composed.  The  depth  of 
this  percolating  water,  or  the  form  of  the  curve  DEC  (Fig  68),  depends 
primarily  upon  the  uniformity  of  the  material  and  not  upon  its  fineness 
or  the  quantity  of  water  passing.  Since  the  weight  and  stability  of  a 
dam  are  decreased  by  this  percolating  water  it  is  evidently  of  advantage 

*  See  paper  by  Ross  and  Broenniman  on  the  Hydrostatic  Pressure  in  Masonry. 
Jour.  West.  Soc.  Engrs.,  1897,  n.  p.  449. 


342  EARTHEN  DAMS,  v 

either  to  prevent  percolation  altogether  or  to  lower  the  water  level 
DEC  as  much  as  practicable.  In  the  case  of  low  earthen  dams  it  is 
important  to  keep  this  line  low  and  also  to  reduce  the  amount  of  per- 
colation to  a  small  quantity,  as  any  considerable  amount  of  percolating 
water  appearing  along  the  lower  face  BC  is  likely  to  affect  seriously 
the  stability  of  the  material  in  this  part  of  the  dam. 

Now  the  slope  of  the  curve  DEC  at  any  point  measures  the  relative 
resistance  to  flow  of  the  percolating  water,  hence  anything  which 
increases  this  resistance  tends  to  increase  the  slope  of  the  curve.  An 
increased  resistance  near  the  up-stream  side  will  thus  cause  the  curve 
to  take  some  such  form  as  DE'C.  This  result  is  accomplished  in 
various  ways.  In  an  earthen  dam  the  material  near  the  up-stream 
side  may  be  made  more  impervious  than  that  in  the  lower  part  of  the 
dam,  while  in  a  masonry  dam  the  upper  face  may  be  plastered  or  other- 
wise made  relatively  impervious.  The  drainage  of  the  lower  portion 
of  the  dam  in  the  case  of  either  an  earthen  or  masonry  structure,  is 
another  means  for  lowering  the  water-level  and  at  the  same  time  taking 
care  of  the  percolating  waten  Where  porous  material  must  be  used 
the  amount  of  percolation  is  kept  within  safe  limits  by  making  the  dam 
of  great  width.  Core  walls,  if  made  relatively  impervious  (see  Art. 
385)  will  serve  to  lower  the  water-level  in  the  material  below  the  wall, 
but  if  the  wall  is  not  more  impervious  than  the  earth  filling  below  then 
it  will  have  little  influence  in  this  respect. 

In  Fig.  68  it  has  been  assumed  that  the  foundation  is  somewhat 
porous  as  well  as  the  dam.  In  that  case  the  percolating  water,  if  not 
large  in  amount,  may  pass  down  stream  entirely  below  the  surface  and 
give  no  trouble ;  otherwise  it  will  come  to  the  surface  near  the  toe  of 
the  dam  in  the  face  BC  or  will  appear  below  C  as  springs.  If  the 
foundation  be  entirely  impervious,  then  any  percolating  water  must 
appear  along  the  face  BC,  the  ground-water  level  intersecting  the  face 
BC  at  some  point  Ft  -depending  upon  the  nature  of  the  construction 
as  above  explained.  In  either  case  special  care  must  be  exercised  in 
the  construction,  as  explained  more  fully  in  Art.  400. 

Some  very  instructive  observations  were  made  in  1901  on  several 
of  the  earthen  dams  of  the  New  York  Water  Supply  relative  to  the 
water  level  therein,  by  sinking  small  drive  pipes  at  various  points  in 
the  bank.  Fig.  68 a  shows  the  results  in  the  case  of  four  of  the  dams 
tested.  The  dams  are  all  built  with  core  walls  and  the  effect  of  such 
walls  on  the  water  level,  as  shown  in  these  examinations,  is  of  much 
interest.  In  the  figure  the  water  level  in  each  test  well  is  shown  and 
between  wells  it  is  assumed  to  be  a  straight  line.  In  the  Titicus  dam 


ADVANTAGES  AND  REQUISITE    CONDITIONS. 


343 


and  the  Car m el  Auxiliary  dam  the  water  level  falls  abruptly  at  the 
core  wall,  but  in  the  other  dams  the  wall  seems  to  have  little  effect  upon 
the  water  surface.  In  the  former  case  the  wall  is  evidently  more 
impervious  than  the  earth  below,  while  in  the  latter  case  it  is  not. 
Whether  this  is  due  to  a  more  porous  filling  it  is  impossible  to  say. 
For  maximum  stability  the  condition  of  the  first  two  dams  is  the  more 
favorable.  In  the  Amowalk  dam  the  test  wells  Nos.  13  and  14  indicate 
that  the  percolating  water  flows  away  below  the  surface,  while  in  the 


Middle  Branch  Dam-    Reservoir  G. 
Compute!  Oct.  «».    rirst  Filled  end  Available  1678. 


Upcf. 


603   Brook  Dam   No.  I   -    Reser 

COfpltM  Sept.,  l89I.t!rsiritM<H>dMk>HtArrin9K.fyrvtl.) 


Slope  Sffptr  lOO' 


Carmel  Auxiliary  Dam- Reservoir  D. 
CcmpStttd  Jan.,1896.  First  FWedantl  Anitaklt  ApK,19.ie96.(Fvttl 


•Titicus  Dam  -    Reservoir  M. 
C<mp!cM  Jvt/«95.  First  FHM  and  Available  Jan.  t895.(^Full.J     TopofS 
Maximum  Section. 


..    "hoof SpillvxQ(_ 


Carmel    Main   Dam  -  Reservoir  D 

Cv*?ltlialJo*J996F,ntr,lltd<u«liHH>il9blt  April  I9, 


50' 


Amawalk   Dam  -    Reservoir-    A.      *&¥** 

Completed  1990.    F,rst  Fill€d  and  Ava,ldt>l»    169J.(*/4-FvU) 


&' per  100' 


FIG.  68a.  —  SECTIONS  OF  DAMS   IN  CROTON  VALLEY  SHOWING  GROUND-WATER   LEVEL. 

(From  Engineering  Record,  Vol.  XLIV.) 


Middle  Branch  dam  it  appears  to  come  to  the  surface  along  the  face 
of  the  bank.  The  difference  in  condition  would  seem  to  be  due  to  a 
difference  in  amount  of  percolation  or  to  different  porosities  of  the 
underlying  material.  Evidently  by  the  use  of  suitable  material,  or  by 
proper  drainage,  the  water  level  could  be  brought  down  as  in  the 
Amowalk  or  the  Titicus  dam.* 

380.  Advantages  and  Requisite  Conditions. — -•  The  earthen  embank- 
ment is  the  most  common  form  of  dam.  It  can  be  built  on  a  variety 
of  foundations ;  it  is  commonly  the  cheapest  form,  and  when  well 
designed  and  executed  is  an  entirely  safe  and  reliable  structure.  The 
stability  of  an  earthen  dam  is,  however,  so  closely  dependent  upon  its 
imperviousness  that,  compared  to  some  other  forms  of  dams  in  which 

*  See  report  of  Engineers  on  Changes  in  the  New  Croton  Dam,  Eng.  Record, 
1901,  XLIV.  p.  520;  Eng.  News,  1901,  XLVI.  p.  410.  Also  discussion  in  Eng.  News, 
1901,  XLVI.  p.  454,  and  1902,  XLVII.  p.  33  ;  and  Trans.  Am.  Soc.  C  E.,  1906,  LVI.  p.  32. 


344  EARTHEN  DAMS. 

these  functions  are  more  independent,  the  necessity  for  making  the 
dam  impervious  is  relatively  great.  The  properties  of  the  materials 
used  are  also  less  uniform  and  less  well  known  than  those  of  other 
materials,  so  that  a  very  large  margin  of  safety  must  be  used. 

Where  flood- waters  have  to  be  passed  over  a  dam  some  other 
material  than  earth  must  be  used  for  at  least  the  portion  of  the  structure 
subjected  to  water  action.  Water  flowing  over  an  earthen  embank- 
ment is  inadmissible,  many  failures  having  been  caused  by  such  occur- 
rence. If  a  suitable  foundation  can  be  had,  masonry  is  to  be  preferred 
for  highl  dams.  It  is  more  reliable,  and  where  great  pressures  occur  it 
furnishes  a  safer  design  for  the  outlet  pipes.  Several  successful  earthen 
dams  have,  however,  been  built  of  a  height  exceeding  100  feet.  Many 
high  dams  have  been  constructed  partly  of  earth  and  partly  of  masonry, 
the  higher  central  portions  being  of  the  latter  material. 

381.  The  general  requirements  of  a  good  foundation  for  an  earthen 
dam  are  that  an  impervious  stratum   can  be  reached  at  a  moderate 
depth,  and  that  the  material  near   the  surface  is  sufficiently  compact 
to    support    the  load.     A  compact    clay  or   hardpan   makes    the  best 
foundation.     Solid  rock    is  also  good  if   not   fissured.     Mere   porosity 
is    comparatively  unobjectionable,  but  a  rock   through  which  water  is 
liable  to  pass  in  cracks  and  fissures  makes  a  very  bad  foundation  for  an 
earthen    dam.     Embankments    of   earth   have   been    successfully   con- 
structed on  foundations  of  sand ;  but  in  such  a  case  it  is  important  that 
the  sand  be  fine  and  of  a  uniform  character,  containing  no  streaks  of 
coarse  material  which  will  offer  little  resistance  to  the  flow  of  water. 
Soft  foundations  have  also  been  built  upon  in  cases  of  necessity,  but 
both  porous  and  soft  materials  should  be  avoided  if  possible. 

382.  Forms  of  Construction.  —  Earthen  dams  are  of  a  trapezoidal 
form  with  top  width,  side  slopes,  etc.,  proportioned  according  to  the 
material  used.     Several  types  of  embankments  are  employed,  the  one 
used  in  any  case  depending  upon  the  material  at  hand  and  upon  the 
individual  preference  of  the  engineer. 

1.  The  .Homogeneous  Embankment. — Where  good   material    is  at 
hand  in  sufficient  quantities  the  entire  embankment  may  be  made  of 
uniform  consistency  and  all  as  nearly  water-tight  as  possible.     Usually, 
however,  it  will  be  more  economical  and  give  as  good  results  to  put 
the  best    material  near   the  upper  side  of   the  embankment,  changing 
gradually  to  the  more  porous  material  towards  the  lower  face. 

2.  Embankments  with  Core-walls.  — Where  good  material  is  scarce, 
imperviousness  is  usually  obtained  by  means  of  a  wall  of   impervious 
earth    or   masonry  placed   near   the   center   of    the  dam.     If    imper- 


FORMS  OF  CONSTRUCTION.  345 

vious  foundation  is  reached  only  at  a  considerable  depth,  this  portion 
only  of  the  embankment  is  carried  to  the  extreme  depth. 

3 .  Porous  Embankments  or  Embankments  on  Porous  Foundations 
are  sometimes  necessary  from  lack  of  suitable  material ;  they  require 
special  precautions  to  insure  their  stability. 

383.  Stability  of  the  Various  Forms  of  Embankments. — The  chief 
danger   of  failure   of  an  earthen  embankment  lies    in   its   destruction 
through  percolation  or  in  being  overtopped  by  floods.     It  is,  however, 
desirable  to  consider  also  the  stability  against  sliding  on  the  base,  and 
in  some  localities  it  is  necessary  to  make  the  design  with  reference  to 
the  possibility  of  overloading  the  foundation  stratum.      The  matter  of 
soft  foundations  will  be  treated  later,  but  the  questions  of  impervious- 
ness  and  frictional  stability  will  be  considered  here. 

The  conditions  would  rarely  be  such  as  to  make  it  likely  that  a  dam 
could  fail  by  actually  sliding  as  a  whole  on  its  base.  Lack  of  stability 
to  resist  water-pressure  would  be  shown  rather  by  slips  of  portions  of 
the  embankment  at  the  outer  slope.  The  stability  in  this  respect  is, 
however,  approximately  indicated  by  the  frictional  stability  at  the  base 
and  at  other  horizontal  sections. 

384.  The  Embankment  Without  Core-wall. — In  case  the  embank- 
ment is  impervious,  either  when  made  entirely  of  impervious  material 
or  when  only  the  upper  portion  is  so  made,  the  internal  water-pressure 
is  zero,  as  it  is  assumed  that  no  water 

percolates.       The    forces    acting   will      ^P 
then   be   as  shown   in    Fig.    69.     The          - 
force  tending  to  cause  sliding  along  the 
base    is    P  sin    a,   and  the   maximum 
resistance    would    be     Vc,    where  c  =  FIG.  69. 

coefficient  of  friction  of  the  material.  Here  V  is  large,  being  equal  to 
W  +  P  cos  «,  hence  the  factor  of  safety  against  sliding  is  in  this  form 

relatively  large  and  equal  to    -— — : -      If  imperviousness  is  not  per- 

P  sm  a 

fectly  secured  in  a  homogeneous  dam,  water-pressure  will  exist  within 
it  which  will  reduce  the  effective  weight  of  the  material,  as  explained 
in  Art.  378.  It  was  also  there  shown  that  to  avoid  this  as  much  as 
possible  the  upper  portion  should  be  more  impervious  than  the  lower 
portion.  In  this  way  great  stability  can  be  secured  with  porous 
materials. 

385.  The  Embankment  with  Core-wall.  —  In  this  form  reliance  is 
chiefly  placed  on  the  core  for  imperviousness.     If  it  is  placed  at  the 
centre,  as  in  Fig.  70,  and  is  more  impervious  than  the  material  above  it, 


346 


EARTHEN  DAMS.  ' 


the  line  of  pressure,  AB,  on  the  up-stream  side  must  be  assumed  nearly 
horizontal.  If  the  material  below  the  core  be  relatively  porous,  as  it 
should  be,  then  there  will  be  no  water  in  the  lower  portion  of  the  dam. 
The  water-pressure  will  then  be  applied  practically  horizontally  on  the 
core-wall,  and  dependence  for  stability  against  sliding  must  be  placed  on 
the  wall  and  material  below.  In  Fig.  71  is  shown  the  part  of  the 
embankment  below  the  upper  face  of  the  core-wall.  Let  h  =  depth 
of  water  ;  bh  =  width  of  this  portion  of  the  dam  at  water-level  ;  s  = 
slope  of  outside  face  in  terms  of  ratio  of  horizontal  to  vertical  projection  ; 
w  =  weight  of  a  unit  volume  of  water  ;  w*  =  weight  of  a  unit  volume 


bh  .......  J 


FIG.  70.  FIG.  71. 

of  dry  embankment  material ;  and    W  =  weight  of  a  slice  of  embank- 


coefficient of 


ment  one  unit  long.    The  pressure  of  the  water  will  be  P=* •       The 

weight  of  embankment  =  W  =  w'hibh  +    — J  .       If 
friction,  the  factor  of  safety  against  sliding  is 


rf 

2 


If   the   slope  s  is  made  as  steep  as  the  material  will  stand,  then 
c  =  -  and  the  factor  of  safety  becomes  equal  to 


w 


(I   +  2bc). 


If  w'  =  100  pounds  per  cubic  foot,  and  w=  62.5  pounds,  then  to 
secure  a  factor  of  two  would  require  b  to  be  equal  to  * — -  .  If  c  = 
\(s  =  2:1),  this  would  give  a  value  of  b  equal  to  .25;  that  is,  the 


MATERIAL   FOR  EMBANKMENTS.  347 

width  at  the  water-line  must  equal  .25^.  Usually  the  width  is  greater 
than  this.  To  further  increase  the  stability  the  outside  slope  should 

be  made  greater  than  — .      It  should  thus  be  made  about  2  to  I  if  the 

material  will  just  stand  at  I \  to  I  (c  =  f).  With  s  =  2  and  c  =  f,  a 
factor  of  safety  of  2  would  be  secured  with  b  —  o. 

In  this  discussion  the  possible  pressure  of  water-soaked  material 
upon  the  core-wall  has  been  neglected.  What  this  would  be  is 
impossible  to  say,  but  before  sliding  could  take  place  it  would  also 
have  a  downward  component  against  the  wall,  thus  adding  to  the  fric- 
tion. The  above  analysis  is,  however,  sufficient  to  show  the  desira- 
bility of  rather  flat  slopes  on  the  down-stream  side,  a  considerable 
width  at  the  water-line,  and,  in  order  to  secure  the  full  benefit  of 
weight,  the  lower  half  of  the  embankment  should  be  relatively  porous 
and  heavy.  It  is  also  plain  that  the  weakest  section  is  at  the  bottom. 

386.  Material  for  Embankments. — Various  kinds  of  material  can  be 
used  to  make  an  embankment.  Loam,  sand,  gravel,  and  clay,  mixed 
in  various  proportions,  are  common.  For  the  first  three  to  be  imper- 
vious they  must  contain  a  certain  proportion  of  clay,  the  amount 
required  depending  upon  the  variation  in  size  of  the  coarser  particles. 
The  suitability  of  a  material  for  embankment  construction  can  to  some 
extent  be  determined  by  experiments.  It  should  be  strongly  cohesive 
and  plastic  when  mixed  with  water,  and  should  be  impervious ;  but  the 
correct  valuation  of  natural  mixtures  requires  much  experience  in  their 
actual  use  in  construction.  If  sufficient  impervious  material  is  not 
available  to  form  the  entire  embankment,  the  best  is  to  be  selected  for 
this  purpose  and  confined  to  the  upper  portion  or  to  a  puddle  core. 
For  the  lower  portion,  coarse  heavy  material  is  suitable. 

Considerable  difference  of  opinion  exists  among  engineers  as  to  the 
best  material  for  embankments  or  core-walls.  English  practice  favors 
a  puddle  of  clay  with  little  or  no  gravel,  while  most  American  engineers 
favor  a  gravel  and  clay  puddle.  Impervious  cores  or  embankments 
can  be  made  of  either  material,  and  where  fully  protected  from  wash, 
and  from  becoming  dried  out,  are  equally  satisfactory.  Clay  shrinks 
greatly  in  drying,  thus  forming  cracks,  and  a  pure  clay  will  shrink  much 
more  than  a  mixture  containing  only  15  or  20  per  cent  of  clay,  an 
advantage  in  favor  of  the  mixed  material.  The  latter  is  also  much  the 
safer  against  wash  in  case  of  leaks,  and  is  more  suitable  for  the  main 
body  of  the  embankment  and  for  use  in  exposed  situations.  It  is  also 
less  easily  attacked  by  wpodchucks,  muskrats,  etc.  Clay  dissolves 
and  washes  away  very  easily  on  account  of  the  minute  size  of  the 


EARTHEN  DAMS. 

particles.  It  is  therefore  very  essential  to  the  stability  of  a  clay  wall 
that  there  be  no  percolation  through  it.  For  confined  locations  and 
in  thin  sections,  a  clay  containing  only  coarse  sharp  sand  is  probably 
better  than  one  with  gravel. 

If  good  material  does  not  exist  already  mixed,  artificial  mixtures 
of  gravel,  sand,  and  clay  may  be  used.  A  fairly  uniform  sand  or 
gravel  contains  about  40  per  cent  of  porous  space.  If  then  a  mixture 
be  made  of  coarse  gravel,  fine  gravel,  and  sand,  in  each  case  just 
enough  of  the  finer  material  being  used  to  fill  the  interstices  of  the  next 
coarser,  there  will  be  in  the  mixture  a  porous  space  equal  to  .40  X  -40 
X  .40  =  6.4  per  cent,  which  will  represent  the  proportion  of  clay 
necessary  to  make  the  mixture  impervious.  In  practice  it  will  take 
considerably  more  to  insure  the  filling  of  all  the  interstices,  as  much 
as  I  5  or  20  per  cent,  depending  upon  the  nature  of  the  gravel  mixture. 
In  any  case  the  percentage  of  voids  in  an  artificial  mixture  can  be 
readily  determined  by  tests  with  water. 

Porous  embankments  may  be  formed  of  sand,  gravel,  or  loam,  and 
if  properly  constructed  are  in  some  respects  safer  structures  than  one 
made  largely  of  clay.  If  the  material  is  properly  graded  from  fine  to 
coarse  from  the  upper  side  to  the  lower,  the  fine  material  will  act  to 
prevent  water  coming  through  with  sufficient  velocity  to  wash  away 
the  coarser  particles  below  which  furnish  stability  to  the  structure. 

387.  Core-walls. — Puddle  Cores. — Much  has  been  written  regarding 
the  use  or  omission  of  core-walls,  and  the  material  of  which  they  should 
be  made.  Theoretically,  core-walls  are  needed  only  when  the  body 
of  the  embankment  cannot  readily  be  made  water-tight.  With  an 
abundance  of  good  material  there  is  no  object  in  using  a  core-wall  of 
earth  except  perhaps  that  the  chances  of  getting  good  work  done  are 
better  if  attention  is  concentrated  on  a  small  section.  With  a  smaller 
quantity  of  good  material  it  is  best  to  concentrate  it  in  a  body,  and 
with  material  still  more  scarce  it  will  naturally  be  placed  in  a  wall  or 
puddle  core.  As  between  a  bank  in  which  the  clay  is  confined  to  a 
narrow  wall,  and  one  where  the  same  amount  is  mixed  with  a  suitable 
proportion  of  gravel  and  forms  a  larger  part  of  the  embankment,  the  latter 
will  be  preferable.  In  deep  trenches,  and  especially  where  much  water 
is  met  with,  a  concrete  filling  is  frequently  used  for  a  part  of  the  depth. 

For  a  puddle  wall  the  minimum  thickness  ordinarily  used  is  4  to  8 
feet  at  the  top  and  about  one-third  the  depth  of  water  at  the  bottom, 
with  a  uniform  batter  on  both  faces.  The  trench  is  also  usually  made 
with  a  batter,  the  width  at  the  bottom  being  one-third  to  one-half  that 
at  the  ground-level,  with  a  minimum  of  4  or  5  feet. 


CORE-  WALLS. 


349 


388.  In  Fig.  72  is  illustrated  the  embankment  of  a  distributing 
reservoir  at  Syracuse,  N.  Y.,  built  with  a  low  core-wall.  The  material 
composing  the  body  of  the  embankment  was  a  mixture  of  heavy  clay 
and  a  small  amount  of  gravel.  All  hard  lumps  were  broken  up  and  all 
stones  more  than  4  inches  in  diameter  were  removed.  The  trench  was 


FIG.  72. — SECTION  OF  RESERVOIR  EMBANKMENT,  SYRACUSE,  N.  Y. 

about  8  feet  deep  and  12  feet  wide,  and  was  filled  with  clay  in  4-inch 
courses  puddled  in  place. * 

An    embankment    with    full    puddle    core    and  •  selected    material 
adjacent  is  shown  in  Fig.  73,  which  is  a  section  of  a  reservoir  embank- 


HW. 


FIG.  73. — SECTION  OF  RESERVOIR  EMBANKMENT,  GLASGOW  WATER-WORKS. 

ment  at  Glasgow,  Scotland. t  The  foundation  stratum  was  of  exceed- 
ingly varying  nature,  and  at  one  place  the  trench  was  carried  to  a  depth 
of  195  feet. 

389.  Masonry  Core-walls. — Instead  of  a  core  of  puddle,  many 
engineers  prefer  a  core  of  rubble  masonry  or  of  concrete,  made  as 
impervious  as  possible.  The  advantages  of  this  over  a  core  of  puddle 
are  its  safety  against  attack  by  burrowing  animals,  safety  against  wash 
in  case  minute  leaks  occur,  and  the  greater  certainty  with  which  a  con- 
crete wall  can  be  made  impervious,  especially  where  it  joins  the  foun- 
dation. It  is  also  much  better  suited  for  placing  in  wet  trenches,  and, 
its  thickness  being  less,  the  trench  need  not  be  as  wide.  Furthermore, 

*  Trans.  Am.  Soc.  C.  E.,  1895,  xxxiv.  p.  37. 
f  Engineering,  1894,  LVII.  p.  704.- 


35° 


EARTHEN  DAMS 


in  case  of  an  overflow  the  failure  of  the  dam  will  be  much  delayed  by 
a  wall  of  masonry.  The  chief  objections  raised  against  it  are  its 
greater  cost  and  the  fact  that  with  it  the  bank  is  less  homogeneous  and 
hence  more  difficult  to  construct,  and  more  subject  to  injury  by  unequal 
settlement.  Core-walls  if  made  too  thin  are  also  liable  to  rupture  from 
unequal  earth-pressures.  For  these  reasons  it  is  even  more  important 
to  avoid  much  settlement  by  a  very  careful  compacting  of  the  material 
than  in  the  case  where  the  embankments  are  entirely  of  earth. 

On  the  whole,  the  practice  in  the  eastern  part  of  the  country 
strongly  favors  masonry  core-walls,  especially  for  high  embankments, 
and  many  engineers  would  use  them  as  an  extra  precaution  even  where 
the  entire  embankment  is  of  good  material.  In  the  West  they  are 
seldom  used,  and  some  of  the  highest  embankments  have  been  con- 
structed without  them. 

Core-walls  should  be  made  with  a  batter,  as  this  tends  to  prevent 
the  separation  of  earth  and  masonry  from  settlement.  Short  buttresses 
constructed  at  intervals  on  the  up-stream  side  are  an  additional  precau- 
tion against  the  passage  of  water  along  the  face  of  the  core-wall. 

To  secure  imperviousness  the  concrete  should  be  relatively  rich  in 
mortar,  and  it  is  also  advisable  to  plaster  the  upper  face  with  neat 
Portland-cement  mortar.  This  is  the  practice  of  the  Boston  Water 
Board,  and  experiments  on  certain  dams  thus  constructed  show  little 
water  in  the  bank  below  the  core. 

Masonry  core-walls  are  made  of  various  widths.  Sometimes  in 
case  of  embankments  made  of  good  material,  they  are  made  only  a  foot 


FIG.  74. — SECTION  OF  DAM  No.  5,  BOSTON  WATER-WORKS. 

or  two  thick,  their  purpose  being  mainly  to  prevent  the  passage  of 
burrowing  animals.  Ordinarily,  however,  a  core-wall  is  made  2  to  4 
feet  thick  at  the  top,  with  a  batter  of  -J  to  f  inch  per  foot  on  each  side 
down  to  the  trench  and  then  with  vertical  faces  below.  The  height  of 
a  core-wall  should  be  equal  to  that  of  the  highest  water-level. 

390,  Fig.  74  is  a  section  of  the  earthen  portion  of  Dam  No.  5  of  the 
Boston  Water-works,  and  represents  what  may  be  considered  as  the 


CORE-WALLS. 


351 


most  advanced  practice  in  this  type  of  construction.*  Fig.  75  is  the 
section,  as  designed,  of  the  earthen  portion  of  the  New  Croton  Dam. 
The  masonry  core  extends  to  solid  rock.  The  dam  as  constructed  is 
not  so  high  above  foundation  as  the  section  shown. t 

391.  Core-walls  of  Wood  and  Steel.—  Sheet-piling  is  sometimes 
used  to  good  advantage  in  the  bottom  part  of  an  embankment,  but  to  be 
durable  it  must  be  in  a  position  where  it  will  be  kept  constantly  wet. 
It  is  especially  serviceable  with  low  embankments  built  on  a  porous 
foundation  and  in  temporary  work. 

A  core  of  steel  imbedded  in  concrete  has  been  used  in  a  rock-fill 
dam  at  Otay,  Cal.  The  steel  varied  in  thickness  from  No.  o  to  No.  3, 
Birmingham  gauge  (.34  inch  to  .259  inch).  The  plates  were  riveted 
and  calked  and  coated  with  asphalt.  This  steel  core  was  protected 


FIG.  75. — DESIGN  FOR  NEW  CROTON  DAM. 

on  each  side  by  a  wall  of  concrete  I  foot  thick.  (See  Art.  455.) 
Such  a  wall  in  an  earthen  embankment  would  be  absolutely  safe  against 
percolation  even  though  slight  cracks  should  form  in  the  masonry. 
Compared  to  a  wall  entirely  of  masonry  it  could  be  made  much  thinner 
for  the  same  strength,  and  as  the  cost  of  a  J-inch  plate  would  not  be 
more  than  the  cost  of  I  or  2  feet  of  concrete,  a  considerable  saving 
could  be  effected.  At  the  bottom  and  ends  of  the  dam  the  masonry 
wall  should  spread  out  to  the  ordinary  width.  In  a  thick  core-wall 
the  riveting  and  calking  of  the  plates  might  be  dispensed  with. 

392.  Position  of  Core-ivalls.  —  In  embankments  for  impounding- 
reservoirs  core-walls  are  usually  placed  at  or  near  the  centre  of  the 
dam.  The  effective  weight  of  the  structure  would  evidently  be 
increased  by  placing  it  near  the  up-stream  face,  and  this  is  sometimes 

*  Eng.  News,   1895,  xxxm.  p.  230. 

t  Trans.  Am.  Soc.  C.   E.,  1900,  XLIII.  p.  469;  also  1906,  LVI.  p.  32.      See  Eng, 
News,  1904,  LI.  p.  335,  for  example  of  steel  core  in  an  earthen  embankment. 


35  2  EARTHEN  DAMS. 

done  where  made  of  puddle.  The  disadvantages  of  so  doing  are  that 
much  more  puddle  is  required  for  the  same  thickness,  it  is  not  so  readily 
placed,  and  is  more  exposed  to  frost  and  water  action  and  to  drying 
out  when  the  water  is  low.  There  is  also  more  danger  of  slips  when 
the  water  is  drawn  down,  such  as  have  occurred  in  several  places. 

393.  Embankment  Slopes.  —  Much  variation  exists  in  practice  in  the 
matter  of  side  slopes,  even  with  similar  material.      On  the  water  side 
the  slope  is  usually  protected  from  wave  action  and  should  only  be 
sufficient  to  prevent  slips.     With  coarse  material  this  need  not  be  flatter 
than  2  horizontal  to  I  vertical.      With  finer  material  it  may  need  to  be 
2j  or  3  to  I,  or  in  some  cases  even  4  to  I,  since  earth  in  a  saturated 
condition  has  a  comparatively  small  angle  of  repose.      On  the  lower 
side  the  material  will  be  dry  if  made  more  porous  than  the  upper  por- 
tion, and  the  angle  of  repose  will  be  about  i^  to  I,  but  the  stability  of 
the  embankment  is  largely  dependent  upon  the  lower  half,  as  pointed 
out  in  Art.  385,  arid  it  is  desirable  to  use  a  somewhat  flatter  slope  than 
that  at  which  the  material  will  just  stand.      A  slope  of  2  to  I  is  there- 
fore to  be  recommended,  although    i£  to   I  has  frequently  been  used. 
If  the  material  will  stand  at  I  to  I  ,  as  broken  stone,  for  example,  then 
a  slope  of  \\  to  I  would  be  suitable.      On  high  embankments,  bermes 
placed  30  to  40  feet  apart  vertically  are  a  desirable  feature.      On  the 
up-stream  side  they  form  additional  supports  for  the  paving,  while  on 
the  down-stream  side  they  allow  of  lateral  drainage  by  means  of  paved 
gutters,  thus  protecting  the  slope  to'  a  considerable  extent  from  scour 
due  to  heavy  rains.      This  arrangement  also  gives  a  little  greater  safety 
and  stability  at  the  bottom  of  the  embankment  where  it  is  the  weakest. 
Below  the  berme  the  slope  is  often  made  flatter  than  above,  thus  secur- 
ing some  additional  width  with  little  extra  cost.     This  modified  form  is 
particularly  adapted  to  soft  foundations. 

394.  Height  above  Water-line.  —The  top  of  the  dam  should  extend 
sufficiently  above  the  high-water  line  to  protect  the  material  exposed 
to  water  action  from  frost  and  to  give  a  safe  margin  .against  overflow- 
ing.     This  will  be  equal  to  the  depth  reached  by  frost  plus  an  allow- 
ance of  2  to  5  feet  for  wave  action,  depending  on  the  exposure  to  winds 
and  the  depth  of  the  water.     A  formula  given  by  Stephenson  for  height 
of  waves  in  such  cases  is 


in  which  H  =  height  in  feet  and  D  =  length  of  exposure,  or  "fetch," 
in  miles.      For  very  low  embankments  the  height  as  determined  above 


EMBANKMENT  SLOPES.  353 

is  not  always  attained,  more  dependence  being  placed  upon  width  of 
top,  which  will  be  relatively  great  in  such  cases.  In  climates  where 
protection  from  frost  is  not  required  there  should  be  a  larger  margin  of 
safety  between  the  highest  waves  and  the  top  of  the  dam,  as  an  earthen 
embankment  must  not  be  overtopped  by  the  water. 

395.  The  Width  of  Top  is  frequently  fixed    by  requirements  for  a 
roadway.      Where  not  so  fixed  it  is  made  to  vary  with  the  height, — 
from  6  to  8  feet  for  very  low  embankments  to  20  or  25  feet  for  embank- 
ments 80  to   100  feet  high,  or,  approximately,  width  =%  h  -j-  5  feet, 
where  h  =  height  of  dam. 

The  reasons  for  increasing  the  width  with  the  height  of  embank- 
ment are  to  secure  safety  against  the  increased  action  of  waves  and  of 
ice,  and  to  add  to  the  general  stability  of  the  structure.  With  no 
increase  in  top  width  a  high  embankment  would  be  relatively  less 
secure  than  a  low  one,  while  it  is  desirable  to  have  it  the  reverse  on 
account  of  the  much  more  serious  results  of  a  failure  of  a  high  embank- 
ment. 

396.  Preparing  the   Foundation. — In  preparing  the  foundation  the 
surface-soil  must  be  removed  over  the  entire  site  of  the  embankment 
to  a  depth  sufficient  to  reach  good  sound  material.      All  roots,  stumps, 
and  other  perishable  material  must  be  removed,  as  any  such  material 
by  decaying  offers  a  passage  for  water.      For  high  and  heavy  embank- 
ments it  is  important  that  the  excavation  under  the  main  body  of  the 
dam,  and  especially  near  the  core-wall,  be  carried  to  a  very  firm  foun- 
dation in  order  to  avoid  settlement.      Near  the  toes  of  the  dam  the 
weight  is  much  less  and  a  softer  material  will  support  it.      For  the  por- 
tion to  be  occupied  by  the  core-wall,  if  one  is  used,  and  a  certain  width 
in  any  case,  the  foundation  must  be  excavated  to  an  impervious  stratum 
of  solid  rock  or  clay,  and  penetrate  for  a  short  distance  such  stratum. 
Where  disintegrated  and  fissured  rock  is  met  with,  the  construction  of 
a  safe  embankment  requires  the  most  careful  work  in  preparing  the 
foundation.      In  some  recent  cases  trenches  have  been  carried  to  depths 
of  nearly  200  feet  before  a  secure  bottom  has  been  reached. 

A  sound  bottom  having  been  reached  the  surface  should  be 
roughened  in  order  to  give  a  better  bond  with  the  earth  filling ;  and  if 
the  material  is  solid  rock,  all  holes  and  crevices  must  be  thoroughly 
cleaned  and  filled  with  cement  or  concrete.  Springs  of  water  met  with 
on  the  foundation  area  are  often  very  troublesome  and  dangerous, 
especially  if  under  or  near  the  core-wall.  If  flowing  with  a  small  head, 
they  may  be  quite  readily  stopped  up  with  concrete.  If  under  con- 
siderable head,  an  attempt  to  smother  them  at  first  will  likely  cause 


354  EARTHEN  DAMS. 

them  to  break  out  at  some  other  place.  In  such  a  case  they  are  often 
dealt  with  by  confining  the  water  in  a  little  well  of  concrete  or  in  a 
pipe  until  a  few  feet  of  embankment  have  been  built,  then  pumping  out 
the  well  and  quickly  filling  with  concrete.  Sometimes  strong  springs 
have  been  piped  to  the  outside  of  the  embankment,  and  this  can  safely 
be  done  where  they  occur  in  the  down-stream  portion  of  the  dam, 
but  this  is  otherwise  a  doubtful  expedient.*  Whatever  seepage-water 
gets  through  an  embankment  should  run  perfectly  clear,  as  muddy 
water  denotes  a  washing  out  of  the  material. 

397.  Construction  of  the  Embankment. — After  the  foundation  has 
been  prepared  the  trench  is  first  filled  with  the  material  selected.  If 
puddle,  it  should  be  placed  in  4-  to  6-inch  layers  well  rammed,  or 
cut  and  cross-cut  with  thin  spades  reaching  well  into  the  layer  below, 
just  enough  water  being  used  to  render  the  material  plastic.  Where 
puddle  is  used  in  a  narrow  wall  it  is  advisable  to  prepare  it  before 
placing  by  thoroughly  pulverizing  and  tempering  it  with  water,  no 
more  water  being  used  than  absolutely  necessary.  A  pug-mill  is  very 
useful  for  this  purpose,  especially  where  artificial  mixtures  are  em- 
ployed. Puddle  should  be  thoroughly  worked  and  homogeneous.  If 
concrete  is  used,  special  care  must  be  taken  to  secure  thoroughly  good 
work  in  mixing  and  ramming,  and  in  filling  all  irregular  spaces  in  the 
excavation. 

After  the  core  is  built  to  the  surface,  or  a  little  above  in  the  case 
of  concrete,  the  main  embankment  is  started.  If  the  material  used 
varies  in  quality,  the  finer  and  better  should  be  placed  above  and 
adjoining  the  core-wall,  and  the  coarser  placed  on  the  down-stream 
side  and  near  the  faces.  If  no  core-wall  is  used,  the  better  material 
should  still  be  placed  in  the  up-stream  portion  of  the  embankment. 
Stones  exceeding  3  or  4  inches  in  diameter  should  not  be  allowed  in 
the  embankment  except  along  the  faces.  The  embankment  is  com- 
pacted usually  by  placing  the  material  in  layers  6  to  12  inches  thick, 
wetting,  and  rolling  with  a  heavy  grooved  roller  weighing  200  to  300 
pounds  per  lineal  inch.  These  rollers  are  often  made  by  stringing  cast- 
iron  disks  on  an  axle,  the  alternate  disks  being  2  or  3  inches  different 
in  diameter.  Specially  made  rollers  can  also  be  had  for  this  purpose. 

Much  importance  is  attached  to  the  work  of  compacting,  and  only 
by  the  best  of  supervision  can  good  work  be  secured.  The  use  of 
water  should  be  just  sufficient  to  render  the  material  plastic  and 
capable  of  being  packed,  and  no  more.  An  excess  of  water  makes 
rolling  more  difficult  and  increases  subsequent  settlement.  Many 

*  See  description  of  Tabeaud  dam,  Ehg.  News,  1902,  XLVIII.  p.  26. 


HYDRAULIC  DAM-CONSTRUCTION.  355 

apply  the  water  before  the  layer  is  placed,  instead  of  afterwards,  with 
good  results. 

Embankments  have  been  built  of  dry  material,  and  if  thorough 
ramming  could  be  secured,  this  method  would  probably  give  a  bank 
tighter  and  less  liable  to  settlement  than  by  the  use  of  water.  With 
some  material,  however,  it  is  desirable  to  use  a  certain  amount  of  water 
to  reduce  the  lumps.  If  well-compacted,  the  settlement  will  be  very 
slight,  as  small  an  amount  as  \  inch  in  50  feet  having  been  reported 
by  Mr.  FitzGerald.  With  a  masonry  core-wall  it  is  especially  im- 
portant that  the  settlement  of  the  embankment  be  small. 

During  the  construction  of  the  main  body  of  the  embankment  the 
core-wall  if  of  puddle  is  carried  up  simultaneously  therewith,  thinner 
layers  of  material  being  used  in  this  part,  and  more  care  in  rolling. 
A  concrete  core-wall  must  be  kept  a  few  feet  in  advance  of  the  earthen 
portion,  and  the  latter  well  rammed  against  it. 

398.  Hydraulic  Dam-construction. — In  the  western  part  of  the 
country  many  good  embankments  have  been  built  by  this  method. 
The  material  is,  where  practicable,  obtained  from  the  adjacent  hillsides, 
from  which  it  is  loosened  by  a  water-jet  and  conveyed  to  the  top  of  the 
dam  by  water  flowing  through  pipes  or  flumes.  There  it  is  allowed  to 
settle  in  a  pond  maintained  by  keeping  the  edges  of  the  dam  higher 
than  the  centre.  The  cost  of  construction  where  the  conditions  are 
favorable  is  exceedingly  low. 

The  following  description  of  a  dam  constructed  at  Tyler,  Texas, 
will  further  explain  the  process :  * 

The  dam  is  575  feet  long,  32  feet  high,  and  contains  24,000  cubic 
yards,  the  inner  slopes  being  3  to  I  and  the  outer  2  to  I,  with  a  4-foot 
berme  on  the  inside  10  feet  below  the  top.  All  of  the  materials  used 
in  the  dam  were  sluiced  in  from  a  neighboring  hill  at  a  cost  of  4f  cents 
per  cubic  yard,  including  the  plant  and  all  the  appurtenances  of  the 
reservoir.  Water  was  pumped  through  a  6-inch  pipe  and  directed 
against  the  hillside  from  a  nozzle  at  a  pressure  of  100  pounds  per 
square  inch.  The  material  washed  down  consisted  of  65  per  cent  of 
sand  and  35  per  cent  of  clay. 

4 '  In  beginning  the  work  a  trench  4  feet  wide  was  excavated  through 
the  surface-soil  dowr?  into  clay  subsoil,  a  depth  of  several  feet,  and  this 
was  first  filled  with  selected  puddle  clay  sluiced  in  by  the  stream. 
Then  the  form  of  the  dam  was  outlined  by  throwing  up  low  sand  ridges 
at  the  slope  lines,  which  were  maintained,  as  the  dam  rose  in  height, 

*  From  U.  S.  Geolog.  Survey,  1896-97,  pp.  654-5. 


356  EARTHEN  DAMS. 

by  men  with  hoes.  A  pond  of  water  was  thus  maintained  over  the  top 
of  the  dam,  the  water  being  drawn  off  from  time  to  time,  either  into 
the  reservoir  or  outside  as  preferred.  The  material  was  transported 
from  the  bank  in  a  1 3-inch  sheet-iron  pipe,  with  loose  joints,  stove-pipe 
fashion,  extending  from  near  the  face  of  the  bluff,  where  the  jet  was 
operating,  across  the  centre  line  of  the  dam.  These  were  so  arranged 
as  to  be  easily  uncoupled  at  any  point,  so  as  to  direct  the  deposit  where 
required  to  build  up  the  embankment  uniformly.  It  was  found  that 
the  quantity  of  solids  brought  down  by  the  water  varied  from  1 8  per 
cent  in  solid  clay  to  30  per  cent  in  sand." 

The  entire  cost  of  the  dam  with  all  its  accessories  is  given  at  $i  140. 
Mr.  L.  W.  Wells  was  the  engineer  in  charge. 

399.  Slope  Protection. — The  up-stream  slope  must  be  protected  from 
wave  and  ice  action.      This  protection  is  usually  afforded  by  a  closely 
laid  pavement  about  18  inches  thick  laid  on  6  to   12  inches  of  broken 
stone  or  gravel.      Below  low-water  line  a  good  layer  of  riprap  is  fre- 
quently substituted,  the   paving  ending  at  a  berme.      The  foot  of  the 
paving  should  be  well  supported  by  large  blocks  of  stone  or  concrete. 
Where  large  gravel  and  boulders  are  abundant  the  face  can  be  well 
protected  by  such  material  placed  loosely,  the  larger  stones  being  on 
the  outside  to  resist  the  impact  of  the  ice  and  waves.     Paving  should 
preferably  not  be  put  in  place  until  all  settlement  has  ceased.      (For 
impervious  linings   see   Chapter   XXVII.)     The  down-stream   face  is 
usually  sodded  for  sake  of  appearance  and  as  a  protection  from  rain, 
but  may  be  protected  by  gravel  and  coarse  material  if  more  convenient. 
The  edges  of  the  embankment  should  have  rounded  rather  than  angular 
outlines.     Where  considerable  seepage  exists  it  is  desirable  to  fill  in  at 
the  outer  toe  to  some  depth  with  broken  stone,  as  this  aids  in  drainage 
and  in  maintaining  the  slope. 

400.  Embankments  and  Foundations  of  Porous  Material — Sand  and 
ordinary  porous  earth  have  been  successfully  used  in   embankments  of 
considerable  size.      In  their  construction  it  is  necessary  to  bear  in  mind 
the  effect  of  percolation   on  the   stability,  both  in  tending  to  wash  out 
the  material,  and  to  decrease  its  effective  weight.      Percolation  should 
in  the  first  place  be  limited  as  far  as  possible,  and  to  this  end  the  em- 
bankment should  be  made  broad   and  with  flat  slopes,  especially  on 
the  lower  face  or  the  lower  portion  of  the  lower  face.      The  upper  slope 
may  be  made  as  usual  if  protected  by  paving.      To  prevent  the  mate- 
rial from  washing  out,  the  upper  part  should,  if  possible,  be  made  of 
finer  material  than  the  lower,  the  change  from  one  to  the  other  being 
gradual.     The  velocity  of  the  percolating  water  is  thus  much  less  in 


OUTLET-PIPES.  357 

the  lower  portion  of  the  dam  where  the  material  is  unsupported,  but 
where  the  particles  are  larger  and  less  easily  moved  by  the  water. 

If  the  foundation  is  also  porous,  as  is  apt  to  be  the  case,  it  is  also 
necessary  to  prevent  a  high  velocity  of  percolation  through  it.  This 
is  accomplished  by  the  broad  embankment  which  forces  the  water  to 
pass  farther  through  the  material,  and  can  also  be  aided  by  driving  a 
line  of  sheet-piling  along  the  center  of  the  dam.  The  entire  dam  and 
foundation  should  thus  be  built  like  a  gigantic  filter,  the  object  being, 
in  the  first  place,  to  prevent  percolation  as  far  as  possible  by  the  use  of 
the  finest  available  material  on  the  up-stream  side,  and,  in  the  second 
place,  to  so  support  this  material  as  to  permit  any  percolating  water  to 
escape  without  causing  damage  to  the  dam  or  its  foundation.  In  case 
the  foundation  material  is  very  soft  the  embankment  must  be  spread 
out  to  reduce  the  load  carried.  To  prevent  the  squeezing  out  of  the 
foundation  material,  it  may  be  excavated  to  a  considerable  depth  at 
both  toes  and  replaced  by  gravel  or  concrete.  It  may  also  be  desirable 
to  load  the  earth  to  a  considerable  distance  below  the  embankment 
proper  by  means  of  a  low  bank.  Drainage  at  the  outer  toe  is  service- 
able in  lowering  the  line  of  saturation  and  maintaining  a  drier  slope. 

The  great  Gatun  dam  on  the  Panama  Canal  is  designed  on  the 
principles  here  set  forth.  (See  Fig.  76.)  In  section  it  is  about  135 
feet  high,  with  inner  slope  of  i  :  2  and  outer  slope  of  1:25,  and  a  base 


FIG.  76.  —  SECTION  OF  GATUN  DAM. 

width  of  about  one-half  mile.  It  is  virtually  an  artificial  hill  in  which 
the  percolating  water  will  act  exactly  as  ground- water.* 

401.  Outlet-pipes. — The  design  and  construction  of  the  outlet 
arrangements  is  one  of  the  most  important  and  at  the  same  time  most 
difficult  features  of  the  work.  This  is  chiefly  because  of  the  difficulty 
of  laying  pipes  or  building  masonry  conduits  through  earth  embank- 
ments in  such  a  manner  as  to  secure  a  perfect  and  reliable  connection 
between  the  two  materials.  Poor  work  at  this  point  is  one  of  the  chief 
causes  of  the  many  failures  of  earth  embankments. 

In  reservoirs  of  any  considerable  depth  it  is  desirable  so  to  arrange 
the  outlets  as  to  enable  the  water  to  be  drawn  off  at  different  levels,  not 
exceeding  10  or  15  feet  apart,  in  order  that'water  of  the  best  available 

*  For  a  full  discussion  of  this  subject  see  paper  by  George  Morison  on  the  Bohio 
Dam,  Trans.  Am.  Soc.  C.  E.,  1902,  XL.VIU.  p.  275. 


358 


EARTHEN  DAMS. 


quality  may  at  all  times  be  obtained.  Provision  must  also  be  made 
by  suitable  gates  or  valves  for  controlling  the  flow  or  turning  it  into  a 
conduit  or  other  channel ;  and  to  make  the  operation  as  reliable  as 
possible,  all  valves  or  other  working  parts  should  be  readily  accessible. 

The  outlet-pipes  are  usually  of  cast  iron  and  may  either  be  laid 
underneath  the  embankment  and  surrounded  thereby,  or  a  culvert  of 
masonry  may  be  constructed  in  the  embankment  and  the  pipes  laid 
therein,  or  they  may  be  laid  in  a  tunnel  constructed  in  the  natural 
ground  at  the  end  of  the  embankment  or  at  some  more  remote  point 
in  the  reservoir.  A  gate-chamber  containing  the  necessary  valves  is 
located  at  some  point  along  the  outlet-pipe  or  conduit.  The  size  of 
the  pipe  must  be  such  as  to  deliver  water  at  the  required  rate  without 
too  great  loss  of  head  as  determined  by  considerations  of  economy,  or 
by  the  head  available.  This  will  usually  limit  the  velocity  to  4  or  5 
feet  per  second.  For  large  quantities  two  or  more  outlet-pipes  are  used. 

402.  Pipes  Placed  in  the  Embankment.  —  In  the  case  of  reservoirs 
with  comparatively  low  embankments  the  outlet-pipes  are  usually  laid 
beneath  the  embankment  at  or  near  the  lowest  point.  They  should 
be  laid  on  a  good  firm  foundation  in  the  natural  ground,  and  should 
preferably  rest  upon  and  be  surrounded  by  a  bed  of  8  to  12  inches  of 


FIG.  77.  —  SECTION  THROUGH  OUTLET-PIPE,  NEW  LONDON  RESERVOIR. 

(From  Engineering  Record,  Vol.  XLVI.) 

rich  concrete,  well  rammed  into  the  trench  and  left  rough  on  the  out- 
side. To  enable  the  earth  to  be  more  thoroughly  bonded  with  the 
concrete,  cut-off  walls  should  be  built  projecting  out  from  the  main 
body  of  the  concrete,  i  J  to  2  feet,  as  shown  in  Fig.  77.  If  concrete  is 
not  used,  then  the  pipes  should  be  provided  with  wide  flanges.  They 
should  be  very  carefully  laid  and  tested  under  pressure  before  covering. 
If  the  embankment  has  a  masonry  core-wall,  a  good  secure  connec- 
tion can  readily  be  made  at  this  point  between  pipe  and  embankment. 


OUTLET-PIPES.  359 

If  the  (Tore  is  of  puddle,  great  care  must  be  taken  in  thoroughly  ram- 
ming the  puddle  about  the  concrete.  If  the  trench  extends  below  the 
pipe,  it  should  be  filled  underneath  with  concrete  rather  than  puddle, 
as  otherwise  settlement  and  rupture  are  very  liable  to  occur.  The 
great  difficulty  of  securing  reliable  work  at  this  point,  and  the  failures 
which  have  occurred,  have  led  many  English  engineers  to  strongly 
favor  the  use  of  tunnels. 

403.  Culverts.  -For  some  reasons  an  open  culvert  is  much  to  be 
preferred  to  a  pipe.      Once  constructed,  additional  pipes  may  be  laid 
therein  at  any  time ;  the  pipes  may  also  be  readily  inspected,  and  any 
leaks  that  occur  in  them  do  not  endanger  the  structure,  a  matter  of 
especial  importance  where  the  pipes  are  under  heavy  pressure.     The 
culvert  may  also  be  conveniently  made  to  act  as  a  wasteway  for  the 
stream  during  construction. 

The  same  precautions  must  be  taken  in  the  construction  of  culverts 
as  in  the  laying  of  pipes.  They  must  have  a  good  firm  foundation  and 
a  good  bond  with  the  surrounding  embankment.  The  cross-section 
must  be  amply  strong  to  resist  all  lateral  and  vertical  pressures,  the 
latter  being  assumed  to  act  upwards  as  well  as  downwards,  and,  in  the 
upper  portion  of  the  embankment,  to  be  equal  to  the  full  water-pressure 
of  the  reservoir.  Reinforced  concrete  is  especially  well  suited  for 
work  of  this  character.  Imperviousness  is  secured  by  the  use  of 
a  rich  mortar  and  by  plastering  on  the  outside  with  Portland-cement 
mortar  neat  or  I  to  i.  Cut-off  walls  or  projecting  courses  should  be 
built  around  the  outside  at  intervals  as  described  for  pipe  outlets.  At 
the  connection  with  the  gate-house  a  cut-off  wall  is  put  in  through 
which  the  pipes  pass,  and  which  must  sustain  the  full  head  of  water. 

Fig.  78  illustrates  a  culvert  constructed  through  an  embankment 
of  an  impounding-reservoir,  with  outlet-pipes  laid  therein  and  opening 
into  a  gate-chamber  at  the  upper  toe.  Where  the  gate-chamber  is 
placed  just  above  the  core,  the  culvert  may  stop  at  that  point  and  pipes 
be  used  to  conduct  the  water  from  reservoir  to  gate-house.  Where  the 
water  is  turned  into  the  natural  watercourse  below,  the  pipe  may  be 
dispensed  with,  the  water  passing  through  the  open  culvert. 

The  outlet  arrangements  of  the  new  settling  reservoirs  for  Cincin- 
nati are  shown  in  Fig.  79.  Here  the  culvert  is  constructed  in  the 
natural  ground  and  has  a  very  heavy  section.  A  £-inch  coat  of  Port- 
land-cement plaster  on  the  outside  insures  imperviousness. 

404.  Tunnels. — If  a  tunnel  be   used,   it  may  be  made  straight  and 
pass  underneath   the   embankment,   or  may  turn  an   angle   and   pass 
around  it  altogether  (the   gate-chamber  being  placed  at  the  angle),  or 


36o 


EARTHEN  DAMS, 


it  may  cut  through  a  narrow  place  in  the  divide  and  lead  the  water  into 
another  valley,   a  rare  but  very  favorable   arrangement.     With  deep 


puddle   trenches  or  soft  foundations  it  is  desirable   to   entirely  avoid 
cutting  into  or  under  the  dam. 

If  the  material  through  which  the  tunnel  passes  is  anything  but 


GA  TE-  CHA  MBERS.  361 

hard  impervious  rock,  the  tunnel  must  be  lined  with  brick,  and  back  of 
the  lining  the  excavation  must  be  thoroughly  filled  with  concrete.  In 
rock  a  tunnel  is  entirely  satisfactory,  but  in  earth  it  is  difficult  to  avoid 
disturbing  the  strata,  and  the  back-filling  is  much  more  difficult  than  in 
the  case  of  a  culvert  constructed  in  open  trench.  Sometimes  in  solid 
rock  a  trench  instead  of  a  tunnel  is  dug  around  the  end  of  the  dam,  and 
the  gate-chamber  located  therein. 

405.  Gate-chambers. — The    gates    or  valves    controlling   the   flow 
through  the  outlet-pipes  are  placed  in  small  masonry  chambers,  which, 
besides  allowing  of  convenient  operation  of  and  access  to  the  valves, 
also    usually    contain     screening-chambers    and    valve    arrangements 
whereby  water  may  be  drawn  from  different  levels. 

406.  Position  of  the  Gate-chamber. — Gate-chambers  are  preferably 
placed  at  or  near  the  upper  end  of  the  outlet-pipes  in  order  that  the 
pressure  therein  may  be  under  control.     They  are,  however,  sometimes 
placed  at  the  outer  toe  of  the  embankment,  but  this  is  undesirable,  as 
it  is  impossible  to  shut  off  the  water  from  the  pipes  in  case  of  leakage 
except  by  the  use  of  divers.      This  point  is  of  more  importance  with 
large  dams  than  in  the  case  of  small  distributing  reservoirs.      In  dams 
with  core-walls  the  gate-chamber  may  properly  be  placed  anywhere 
between  the  core-wall  and  upper  toe,  and  with  core-walls  of  masonry 
it  is  conveniently  placed  just  above  and  adjoining  the  masonry  core. 

An  advantage  gained  by  placing  the  chamber  at  the  inside  toe  is 
that  it  enables  arrangements  to  be  easily  made  for  drawing  water  from 
different  levels.  Fig.  78  shows  a  gate-chamber  in  this  position.  A 
foot-bridge  is  here  necessary  to  allow  of  access  to  the  gate-house. 
This  position  exposes  the  chamber  to  severe  stresses  from  the  action  of 
ice  and  is  therefore  more  suitable  for  large  than  for  small  structures. 
If  the  chamber  is  placed  farther  back  in  the  embankment,  the  necessity 
of  a  bridge  is  avoided  and  the  structure  is  much  better  protected  from 
the  action  of  ice,  but  the  drawing  of  water  from  different  levels  is  not 
so  convenient.  It  may  be  drawn  from  the  bottom  by  a  continuation 
of  the  outlet-pipe  or  culvert  to  the  upper  face  of  the  embankment.  It 
can  also  be  drawn  from  near  the  top  by  an  inlet  in  the  masonry  wall  or 
by  a  short  inlet-pipe.  To  draw  from  intermediate  levels,  inlet-pipes  or 
sluices  must  be  extended  to  the  face,  as  in  Fig.  81  ;  or  an  adjustable 
inlet-pipe  may  be  employed,  as  is  common  with  distributing-reservoirs 
and  as  illustrated  in  Fig.  79 ;  or  the  embankment  may  be  removed 
from  the  upper  face  of  the  chamber  and  supported  on  the  sides  by 
heavy  wing  walls,  thus  enabling  the  water  to  be  drawn  through  ordi- 
nary sluiceways  as  in  Fig.  77.  This  last  method  becomes  very  expen- 


362 


EARTHEN  DAMS. 


sive  with  high  embankments.  In  Fig.  81  the  first  and  last  methods 
are  combined. 

407.  General  Arrangements. — The  various  forms  of  gate-chambers 
may  be  further  described  in  connection  with  the  examples  illustrated  by 
the  figures.  The  simplest  form  is  shown  in  Fig.  77,  page  358,  and 
consists  merely  of  a  single  chamber  built  over  the  valve  in  the  single 
outlet-pipe.  A  separate  waste-pipe  is  here  provided.  The  illustration 
refers  to  a  distributing  reservoir,  but  the  arrangement  is  suitable  for 
small  reservoirs  where  screens  are  not  required  and  where  it  is  neces- 
sary to  draw  water  from  but  one  level. 

Fig.   80  illustrates  a  design   suitable  for  small  reservoirs.     This 


Waste  Pip* 
3 


FIG.  80. — GATE-CHAMBER,  IPSWICH,  MASS.     (GOODELL.) 


arrangement  permits  of  drawing  water  from  near  the  bottom  and  from 
about  mid-depth.      Screening  is  also  provided  for. 

Fig.  8 1  illustrates  a  form  adapted  to  larger  works  and  shows  how 
pipes  may  be  arranged  to  draw  from  different  levels  when  the  gate- 
chamber  is  placed  in  the  body  of  the  embankment.  Grooves  are  pro- 
vided for  screens  and  for  stop-planks  for  regulating  the  flow  from  the 
surface  of  the  reservoir.  A  waste-pipe  is  shown  and  also  an  overflow, 


GA  TE-  CHA  MBEhS. 


363 


the  reservoir  in  question  being  a  distributing-reservoir.*     (See  Chapter 
XXVII  for  further  details  of  distributing-reservoirs.) 

In  Fig.  78  is  shown  a  still  more  elaborate  gate-chamber  suitable 
for  the  largest  reservoirs,  and  similar  to  that  used  in  some  of  the  reser- 
voirs of  the  New  York  and  Boston  Water-works.  (See  also  Fig.  99, 
page  397.)  The  structure  is  divided  longitudinally  into  two  cham- 
bers. The  division-wall  contains  the  sluice-valves  for  drawing  water 
at  different  levels,  admission  to  the  outer  chamber  being  through  large 
openings  placed  opposite  the  valves.  In  the  outer  chamber  are  grooves 
for  screens  which  may  also  be  used  for  wooden  stop-planks  in  case  of 
emergency.  As  an  additional  measure  of  safety  the  upper  end  of  the 


FIG.  81.—- OUTLET- CHAMBER,  SYRACUSE  WATER- WORKS. 

inlet-pipe  may  be  provided  with  a  valve  as  shown.  At  the  lower  face  of 
the  dam  is  usually  placed  another  valve-chamber  containing  valves  for 
directing  the  flow  into  waste-pipes,  or  into  a  conduit,  or  otherwise,  as 
the  case  may  be.  This  also  provides  a  more  convenient  place  for  the 
daily  regulation  of  the  flow.  Where  there  are  two  or  three  outlet-pipes 
the  chamber  is  divided  into  a  corresponding  number  of  divisions,  each 
of  them  arranged  to  be  operated  independently.  A  preferable  arrange- 
ment to  that  shown  would  be  to  place  the  gate-chamber  just  above  the 
core- wall,  which  is  the  usual  Boston  practice.  One  of  the  methods 

*  Trans.  Am.  Soc.  C.  E.,  1895,  xxxiv.  p.  46. 


EARTHEN  DAMS. 

described  in  Art.  406  would  then  have  to  be  adopted  if  water  is  to  be 
drawn  from  different  levels. 

Fig.  82  illustrates  a  large  gate-chamber  on  one  of  the  distributing- 
reservoirs  of  the  New  York  Water-supply.  This  design  combines 
many  of  the  desirable  features  already  mentioned.  Note  that  access 
is  had  to  the  pipe-line  from  the  gate-chamber. 

A  form  of  inlet-tower  used  much  in  English  practice  is  shown  in 


.*[<• 


FIG.  8.2. — JEROME  PARK  GATE-HOUSE. 

(From  Wegmann's  "  Water-supply  of  New  York.") 


FIG.  83. — INLET-TOWER,  GLASGOW  WATER-WORKS. 

Fig.  83.  It  consists  of  but  a  single  chamber,  the  inlets  being  placed 
at  various  levels.  A  separate  screen-chamber  is  built  on  shore.*  For 
towers  having  a  single  chamber  the  circular  form  is  to  be  commended. 
Arrangements  differing  considerably  from  those  above  described 
have  also  been  used  with  satisfactory  results.  The  proper  one  to  adopt 

*  Engineering^  1894,  LVII.  p.  738. 


GATE-CHAMBERS.  365 

in  any  particular  case  depends  upon  local  conditions  and  is  determined 
by  considerations  of  safety,  economy,  and  convenience  of  operation. 

Gate-chambers  are  sometimes  entirely  dispensed  with,  and  the 
sluice-gates  built  into  the  sloped  embankments,  with  rods  for  operating 
them  carried  up  the  inclined  face  to  mechanism  above.  This  arrange- 
ment is  suitable  only  in  mild  climates  where  trouble  with  ice  is  not  to 
be  feared.  It  is  cheap,  but  not  as  reliable  or  as  convenient  in  case  of 
stoppage  as  the  gate-chamber. 

408.  Details. — The  masonry  of  the  inlet-tower  is  usually  of  heavy 
rubble,  faced  with  ashlar  and  lined  with  hard  brick  or  cut  stone.  Re- 
inforced concrete  is  also  well  adapted  to  this  work,  as  it  may  be  quite 
closely  calculated  to  resist  the  forces  acting  and  will  usually  effect  con- 
siderable saving  over  the  use  of  stone  masonry. 

The  tower  as  a  whole  when  located  at  the  toe  must  be  able  to  resist 
ice  and  wave  action,  and  each  wall  the  unbalanced  pressure  of  the 
water.  Walls  of  stone  or  brick  masonry  will  vary  in  thickness  with 
their  unsupported  length.  The  exterior  walls  are  usually  made  3  to  4 
feet  thick  at  the  top,  with  an  increase  of  about  three-fourths  inch  to 
I  inch  in  thickness  per  foot  of  depth,  the  batter  being  made  on  the  out- 
side for  convenience  and  to  furnish  a  better  bond  with  the  earthwork. 
Interior  walls  may  be  made  of  slightly  less  thickness.  Reinforced  con- 
crete walls,  where  subject  to  impact  from  ice  or  other  cause,  should  be 
made  considerably  thicker  than  the  static  pressures  require.  The 
foundation  should  be  prepared  with  great  care.  If  the  gate  chamber  is 
placed  near  the  toe,  the  load  will  be  much  heavier  than  the  surrounding 
earth  embankment,  and  unequal  settlement  is  liable  to  occur,  causing 
cracks  in  the  masonry  of  the  culvert  and  displacing  the  outlet-pipes. 
The  bottom  of  the  gate-chamber  should  be  constructed  under  the  sup- 
position that  full  water-pressure  will  exist  underneath  the  chamber  when 
empty.  It  is  best  made  of  reinforced  concrete. 

Fish-screens  are  usually  copper- wire  screens  with  i  to  J  inch  mesh, 
fastened  to  wooden  or  iron  frames  and  arranged  to  slide  in  grooves  in 
the  masonry.  They  are  arranged  in  pairs,  and  each  screen  is  made  up 
of  several  elements  of  a  size  convenient  to  handle.* 

The  gate-chamber  is  surmounted  by  a  gate-house  in  which  is 
located  the  operating  mechanism  of  valves  and  screens.  As  this  build- 
ing is  frequently  quite  prominent,  it  is  important  that  it  be  given  an 
artistic  treatment  suited  to  the  surroundings.  Two  very  commendable 
designs  are  illustrated  on  page  367,  and  show  what  may  be  done  in 

*  For  details  of  screen  and  mechanical  lifter  used  at  distributing-reservoirs  of 
the  Boston  water-works,  see  Eng.  News,  1900,  XLIV.  p.  218. 


366  EARTHEN  DAMS. 

this  direction.  The  former  illustration  is  taken  from  Wegmann's 
"  Water-supply  of  New  York,"  and  the  latter  is  from  a  photograph 
loaned  to  the  authors  by  the  engineer,  Mr.  L.  M.  Hastings. 

The  bottom  of  the  reservoir  should  be  paved  near  the  gate-chamber 
and  the  lower  sluiceway  placed  close  to  the  bottom;  or  a  separate 
drain-pipe  may  be  provided  as  shown  in  the  illustrations.  This  is  a 
necessary  feature  in  small  distributing-reservoirs  requiring  frequent 
cleaning.  If  the  gate-chamber  is-  not  located  at  the  very  bottom  of  the 
valley,  a  drain-pipe  may  lead  to  such  point  and  be  operated  as  a  siphon 
when  it  is  desired  to  drain  the  reservoir.  Where  much  sediment  is 
deposited  it  is  desirable  to  have  a  large  sluice-gate  at  the  very  bottom 
to  use  in  flushing  out  the  material  near  the  dam. 

409.  Valves  and  Sluice-gates. — The  inlets  into  the  gate-chamber 
are  made  to  correspond  in  size  with  the  outlet-pipe.  For  small  inlets 
the  most  convenient  form  is  a  small  piece  of  pipe  built  into  the  walls 
with  an  ordinary  gate-valve  attached  thereto,  as  shown  in  Fig.  81,  or 
a  small  sluice-valve  as  shown  in  Fig.  80.  Large  valves  require  a  good 
broad  support,  and  in  narrow  walls  and  chambers  it  is  more  convenient 
and  also  cheaper  to  use  in  most  cases  cast-iron  sluice-gates  of  the  latter 
form.  These  large  gates  are  usually  of  special  design,  made  with 
ribbed  faces  on  the  side  towards  the  water-pressure,  and  plane  on  the 
other  side,  as  is  ordinarily  done  with  cast-iron  plates.  The  gate  is 
made  to  slide  in  grooves  faced  with  brass  or  bronze,  and  the  sliding 
surfaces  of  the  gate  are  similarly  faced. 

Where  the  water-pressure  tends  to  force  the  gate  off  its  seat,  some 
form  of  wedge  arrangement  must  be  used  to  force  the  gate  to  its  seat 
when  nearly  closed.  Such  an  arrangement  is  shown  in  the  gates  of 
the  St.  Louis  intake  (Fig.  43,  page  265),  the  wedge  being  formed  by 
an  additional  groove  with  brass  facing.  Instead  of  a  continuous 
inclined  groove  such  as  this,  a  series  of  adjustable  blocks  is  sometimes 
employed  against  which  bear  corresponding  projections  on  the  back  of 
the  gate.  When  the  pressure  holds  the  gate  to  the  face  a  simple 
groove  is  sufficient. 

The  frame  of  the  gate  is  usually  of  cast  iron,  bolted  securely  to  the 
masonry,  in  which  case  the  opening  is  lined  with  cut  stone;  or  cast- 
iron  pipes  or  sluices  may  be  built  in  the  masonry  and  at  the  same  time 
serve  as  attachments  for  the  frames.  The  latter  method  is  employed 
at  Syracuse,  and  Fig.  86  illustrates  the  sluice-gate  there  used.* 

Small  sluice  valves  are   operated  by  hand-wheel,   larger  ones  by 

*  Trans.  Am.  Soc.  C.  E.,  1895,  xxxiv.  p.  27. 


FIG.  84.— CENTRAL  PARK  GATE-HOUSE,  NEW  YORK.      (WEGMANN.) 


FIG.  85. — PAYSON  PARK  GATE-HOUSE,  CAMBRIDGE. 


WASTE-WEIRS. 


369 


worm-gearing  proportioned  according  to  the  pressure  and  available 
power.  When  convenient,  hydraulic  power,  using  a  mixture  of  water 
and  glycerine,  as  at  St.  Louis  and  Cincinnati,  is  very  suitable,  each 
cylinder  being  readily  proportioned  according  to  the  load.  The 
cylinders  can  be  so  arranged  that  in  case  of  failure  of  the  pressure 
they  may  be  operated  by  a  hand-pump. 

410.  Waste-weirs, — As  already  noted,  one  of  the  most  fruitful 
causes  of  reservoir  failures  is  insufficiency  of  waste-weir  capacity, 
resulting  in  the  overflowing  of  the  dam  and  its  rapid  destruction. 
Mention  need  only  be  made  of  the  terrible  Johnstown  disaster  in  1889 


o8 


FIG.  86. — SLUICE-GATE,  SYRACUSE  WATER-WORKS. 

where,  on  account  of  insufficient  wasteway,  an  earthen  embankment 
was  destroyed,  resulting  in  the  loss  of  over  2000  lives  and  the  destruc- 
tion of  property  valued  at  3  to  4  million  dollars.* 

In  Chapter  VI  the  subject  of  maximum  flood-flows  was  fully  dis- 
cussed. The  maximum  flood  having  been  estimated,  it  remains  to 
provide  some  safe  means  whereby  it  may  be  passed  to  the  valley  below. 

This  is  done  in  three  different  ways:  (i)  A  wasteway  may  be 
excavated  in  the  natural  ground  at  one  or  both  ends  of  the  dam. 
Where  the  foundation  is  of  rock  this  is  a  very  safe  and  effective  form  of 


*  See  Report  of  Investigating  Committee  in  Trans.  Am.  Soc.  C.  E.,  1891,  xxiv. 
p.  431. 


37°  EARTHEN  DAMS. 

wasteway,  but  care  must  be  taken  to  have  it  of  sufficient  slope  and 
cross-section  at  all  points  to  carry  the  required  amount  of  water  at  the 
assumed  depth.  On  earth  foundations  the  slopes  of  such  a  channel 
would  need  to  be  thoroughly  protected  with  heavy  solid  masonry  in 
cement.  It  will,  however,  seldom  be  economical  to  construct  a  waste- 
way  of  this  kind  in  earth. 

(2)  The  wasteway  may  sometimes  be  formed  at  some  low  point  in 
the  dividing  ridge,  and  the  water  led  to  another  valley.  This  is  likely 
to  require  considerable  attention  in  providing  a  safe  channel  for  the 
increased  quantities  of  water  carried  in  the  other  valley,  particularly  at 
its  upper  end. 

'  (3)  The  third  form  of  wasteway  is  provided  by  making  a  portion  of 
the  dam  of  masonry  designed  as  a  spillway,  and  placed  at  about  the 
axis  of  the  valley.  The  forms  of  such  dams  are  discussed  in  detail  in 
Chapter  XVII.  At  the  junction  of  the  masonry  and  the  earth  portions, 
the  lower  slopes  of  the  embankments  must  be  retained  by  heavy  wing 
walls  built  out  from  the  masonry  dam.  The  upper  slopes  may  be  like- 
wise protected,  or  they  may  be  carried  around  in  front  of  the  masonry 
weir  throughout  its  entire  length.  Where  the  earth  and  masonry  por- 
tions join,  great  care  must  be  taken  to  ram  the  earth  solidly  in  place. 
"°articular  attention  should  also  be  given  to  the  connection  between 
core-wall  and  masonry.-  The  back  of  all  walls  touching  the  earth 
should  be  left  rough  and  be  built  with  a  batter.  The  advantage  of  a 
masonry  core-wall  is  here  obvious.  Fig.  99,  page  397,  shows  the  plan 
of  wing  wall  at  the  junction  of  a  weir  and  an  earthen  embankment 
which  well  illustrates  the  foregoing  points. 

411.  Proportions  of  Waste-weirs. — The    requisite    capacity  being 
known,  the  length  and  depth  of  weir  are  to  be  determined.     Either  may 
be  assumed  and  the  other  computed  by  means  of  a  weir  formula,  but 
in    each    case    there    are    certain    proportions  that  will  be  the    most 
economical.      A  low  weir  requires  a  greater  length,  whereas  a  deep 
and  short  weir  requires,  for  the   same  storage  volume,  that  the  rest  of 
the  dam  be  made  higher.      The  proper  proportions  are  thus  dependent 
upon  the  relative  cost  of  weir  length  and  of  extra  height  of  dam,  and  is 
largely  a  question  of  topography.      Weir  heights  will  ordinarily  range 
from-  2  to  4  or  5  feet,  with  lengths  of  50,  100,  or  even  500  feet,  or  more, 
depending  on  the  required  capacity.      In  any  case  the  flood  line  deter- 
mines the  height  of  the  other  part  of  the  dam,  while  the  weir  crest 
determines  the  storage.      The  difference  is  the  available  depth  of  weir. 
For  weir  formulas  see  Chapter  XII. 

412.  Care  of  Floods  during  Construction. — One  of  the  most  trouble- 


LITERATURE.  37 x 

some  and  expensive  features  of  construction  is  the  provision  for  passing 
the  floods  over  or  through  the  works.  At  the  start  an  artificial  channel 
or  flume  can  readily  be  constructed  at  one  side  of  the  valley,  and  the 
culvert  or  outlet-pipe  put  in  place,  if  there  be  such.  The  ordinary  dis- 
charge and  moderate  floods  can  then  be  passed  through  this.  Heavy 
floods  may  be  allowed  to  pass  over  an  uncompleted  masonry  weir  or 
be  carried  over  the  embankment  at  a  point  protected  by  timber  aprons. 

In  constructing  the  Titicus  dam  of  the  Croton  Water-supply  the 
river  was  first  turned  into  an  artificial  channel  by  means  of  a  temporary 
dam  24  feet  high  and  about  1000  feet  above  the  main  dam.  Afterwards 
a  timber  flume  was  used  having  two  compartments,  each  9  feet  by  7  feet 
9  inches,  placed  25  feet  above  ground  where  it  crossed  the  dam.  After 
the  dam  was  raised  above  the  flume,  the  water  was  turned  into  the 
gate-house  and  discharged  through  two  outlet-pipes  48  inches  in 
diameter.  Extreme  floods  were  allowed  to  pass  over  the  uncompleted 
portions  of  the  masonry  wasteway  at  a  low  point  left  for  the  purpose. 
It  was  considered  that  the  damage  thus  caused  was  less  than  the 
expense  of  constructing  a  flume  large  enough  to  carry  the  water.  Two 
heavy  freshets  were  thus  taken  care  of.  The  tributary  area  was  22.8 
square  miles.* 

413.  Cost. — The  cost  of  reservoir  embankments  when  constructed 
in  the  usual  way  will  range  about  as  follows :  Excavation  25  to  30  cents 
per  cubic  yard;  embankment  30  to  40  cents;  puddle  50  to  75  cents; 
dry  paving  $2.00  to  $3.00;  riprap  $1.50  to  $2.00;  sodding  20  to  30 
cents  per  square  yard.  For  the  cost  of  various  classes  of  masonry  see 
Art.  449  °f the  next  chapter. 

LITERATURE. 
(See  also  Chapter  XXVII.) 

CONSTRUCTION. 

1.  Dorsey.     Excavation  and   Embankment  by  Water-power.     Trans.   Am. 

Soc.  C.  E.,  1886,  xv.  p.  348. 

2.  Henzell.      The  West    Hallington   Reservoir.      Proc.    Inst.   C.    E.,    1890, 

en.  p.  271. 

3.  Follett.      Earthen  vs.   Masonry  Dams.      Eng.  News,   1892,   xxvu.  p.    20; 

Eng.  Record,  1892,  xxv.  p.  400. 

4.  Dam  No.    5  for   the  Additional  Water-supply  of  Boston.     Eng.  News, 

1895,  xxxni.  p.  230;  Eng.  Record,  1893,  xxvm.  p.  361. 

5.  The  Monument  Creek   Reservoir,   Colorado.     £ng.   News,    1893,   xxix. 

P-  235- 

*  Wegmann's  Water-supply  of  New  York,  p.  200 


37 2  EARTHEN  DAMS. 

6.  Herschel.     The  Works  of  the  East  Jersey  Water  Company,  for  the  Supply 

of  Newark,  N.  J.     Jour.  New  Eng.  W.  W.  Assn.,  1893,  vm.  p.  18. 

7.  Le  Conte.      High  Earth  Dams.      Proc.  Am.  W.  W.  Assn.,   1893,  p.  142. 

8.  The  Use  and  Abuse  of  Water  in  the  Construction  of  Reservoir  Embank- 

ments.    Valuable  Discussion.     Jour.  Assn.   Eng.  Soc.,    1894,  xm, 

p.  i56- 

9.  Norboe.     The  Honey  Lake  Valley  Dam,  Cal.     Eng.  News,  1894,  xxxi. 

p.  217. 

10.  Gould.     The  Dunnings  Dam.     Trans.    Am.   Soc.   C.   E.,    1894,    xxxn. 

p.  389. 

11.  Freeman.      Hoisting  Apparatus  of  the  Canal  Headgates  at  Sewall's  Falls, 

N.  H.     Trans.  Am.  Soc.  C.  E.,  1894,  xxxn.  p.  278. 

12.  The  Glasgow  Water-works.      Engineering,   1894,  LVII.  p.  461. 

13..  Taylor.      The  Construction  of  Reservoir  Embankments.     Jour.  New  Eng. 
W.  W.  Assn.,  1894,  vm.  p.  130. 

14.  Dumas.     Etude   sur   les    Barrages-Reservoirs.      Le    Genie   Civil,    1895, 

xxvii.  p.  280. 

15.  Hill.     The  Water- works  of  Syracuse,  N.  Y.     Trans.   Am.    Soc.  C.   E., 

1895,  xxxiv.  p.  23. 

1 6.  Fortier.     Earthen    Dams.     Bulletin    No.    46,    1896,    Utah   Agricultural 

Experiment  Station. 

17.  The  Water-works  of  Colorado  Springs  and  the  Strickler  Tunnel.     Eng. 

News,  1896,  xxxvi.  p.  131. 

1 8.  Watts.     Notes  on  Sinking,  Timbering,  and  Refilling  Concrete  and  Puddle 

Trenches  for  Reservoir  Embankments.      Paper  before  Brit.    Assn. 
W.  W.  Engineers.     Eng.  Record,   1897,  xxxv.  p.  406. 

19.  Paskin.     Discharge  Tunnels  from  Reservoirs.      Paper  before  Brit.  Assn. 

W.  W.  Engineers.      Eng.  Record,   1897,  xxxv.  p.  426. 

20.  Difficulties  with  Earth  Dams  in  Great  Britain.     Abstract  of  a  Paper  by 

W.   Fox  before  the  Soc.  Engineers.      Eng.  Record,    1898,   xxxvm. 
p.  290. 

21.  The  Wachusett  Reservoir  and  Aqueduct.      Eng.  Record,    1898,   xxxvu. 

p.  405. 

22.  The  Kingston,  N.  Y.,  Water-works.     Eng.  Record,  1898,  xxxvu.  p.  341. 

23.  Coppee.     Standard   Levee   Sections.      Trans.    Am.    Soc.    C.    E.,     1898, 

xxxix.  p.  191. 

24.  Strange.     Reservoirs  with  High  Earthen  Dams  in  Western  India.      Proc. 

Inst.   C.    E.,    1898,   cxxxn.    p.    130;    Eng.  Record,    1899,    xxxix. 
p.  448. 

25.  The  Water-works  of  Plymouth,   England.      Eng.  Record,    1899,   xxxix. 

p.  181. 

26.  Knight.     Flood- water  Channel,    Altoona    Reservoir.     Jour.    New  Eng. 

W.  W.  Assn.,  1899,  xiv.  p.   151;  Eng.  Record,  1899,  XL.  p.  386. 

27.  The  Wachusett  Reservoir.     Eng.  Record,   1900,   XLI,   p.    50.     Stripping 

of  the  reservoir  and  construction  of  the  large  dike. 

28.  Quick.     The  High  Earth  Dam  Forming  Druid  Lake,  Baltimore  Water- 

works.    Eng.  News,  1902,  XLVII.  p.  158. 

29.  The  Tabeaud  High  Earth  Dam,  near  Jackson,  Cal.     Eng.  News,  1902, 

XLVIII.  p.  26. 

30.  A   New   Reservoir   at   New   London,  Conn.     Eng.  Record,  1902,  XLVI. 

p.  482. 


L ITERA  TURE.  373 

31.  Morrison.     The    Bohio   Dam.     Trans.   Am.    Soc.    C.    E.,    1902,    XLVII. 

P-  235- 

32.  A  New  Dam  and  Storage  Reservoir  at  Amsterdam,  N.  Y.     Eng.  Record, 

1902,  XLVI.  p.  602. 

33.  An  Earth  Dam  with  Loam  Core,  at  Clinton,  Mass.     Eng.  Record,  1904, 

L.  p.  232. 

34.  Walter.     The  Belle  Fourche  Dam,  Belle  Fourche  Project,  South  Dakota. 

Eng.  Record,  1906,  LIII,  p.  307. 

35.  Gowen.     Changes  at  the  New  Croton  Dam.     Trans.  Am.   Soc.  C.  E., 

1906,  LVI.  p.  32.     See  also  Eng.  News,  1902,  XLVII.  p.  33. 

36.  Schuyler.     Recent  Practice  in  Hydraulic-Fill  Dam  Construction.     Trans. 

Am.  Soc.  C.  E.,  1907,  LVIII.  p.  196. 

FAILURES,    ETC. 

1.  Failure  of  the  Dale  Dike  Reservoir.     From  Rawlinson's  Report.      Van 

Nostrand's  Eng.  Mag.,  1869,  i.  p.  263. 

2.  The  Failure  of  the  Worcester  Dam.     Eng.  News,  1876,  in.  p.   116;    Van 

Nostrand^s  Eng.  Mag.,  1877,  xvi.  p.  54. 

3.  The  Failure  of  a  Reservoir  at   Cleveland,  O.     Eng.  News,  1886,  xvi. 

p.  422. 

4.  Evans.     Beacon    Street    Reservoir,    Lowell   Water-works.     Jour.   Assn. 

Eng.  Soc.,  1886,  v.  p.  297. 

5.  Lukens.     Some  Remarkable  Breaks  in  a  Reservoir.     Proc.  Eng.  Club 

Phil.,  1887,  vi.  p.  147. 

6.  Report  of  Committee  of  Arn.    Soc.  C.  E.  on  the  Cause  of  the  Failure  of 

the  South  Fork  Dam.     Trans.  Am.  Soc.  C.  E.,  1891,  xxiv.  p.  431. 

7.  Expert's  Report  on  the  Reservoir  Failure  at  Lancaster,  Pa.     Eng.  News, 

1894,  xxxii.  p.  462. 

8.  The  Reservoir  Break  at  Portland,  Me.     Jour.  New  Eng.  W.  W.  Assn., 

1894,  VHI.  p.  148;  Eng.  News,  1893,  xxx.  p.  140;  Eng.  Record. 
1893,  xxvin.  p.  186. 

9.  Report  on  Defects  in  the  Queen  Lane  Reservoir,  Philadelphia.     Eng. 

News,  1895,  xxxiv.  p.  102. 

10.  Hill.     A  Classified  Review  of  Dam  and  Reservoir  Failures  in  the  United 

States.     Proc.  Am.  W.  W.  'Assn.,  1902.     Eng.  News,  1902,  XLVII, 
p.  506. 

11.  The  Failure  of  the  Water-works  Dam  at  Utica,  N.  Y.     Eng.  Nevus,  1902, 

XLVIII.  p.  290. 


CHAPTER   XVII. 

MASONRY   DAMS. 

THE   DESIGN. 

414.  General  Conditions. — Dams  of  masonry  can  safely  be  built  only 
upon  very  firm  foundations.      Low  dams  of  a  height  of  20  or  30  feet, 
and  occasionally  higher,  have  been  founded  on  firm  earth,  but  high 
masonry  dams  should  be  constructed  on  nothing  less  substantial  than 
solid  rock.      In  any  case  it  is  necessary  to  prevent  practically  all  settle- 
ment, for  with  a  material  such  as  masonry  any  appreciable  settlement 
is  quite  certain  to  cause  cracks.      Given,  however,  a  firm  foundation,  a 
masonry  dam  is  much  superior  to  an  earthen  embankment  in  several 
respects.      Its  design  can  be  more  certainly  and  precisely  determined 
upon ;  it  is  more  durable ;  outlet  pipes  and  conduits  can  be  constructed 
through  it  with  much   greater  safety;    and,   when  properly  designed, 
flood-waters  may  pass  over  it  without  danger  to  the  structure.      For 
very  high  dams,  such  as  those  above  100  feet,  masonry  is  much  to  be 
preferred.      As   regards    economy,    the   masonry  dam    may    even    be 
cheaper   in   some   cases   than   one   of  earth,   this  question   depending 
mainly  upon  the  convenience  of  obtaining  suitable  material. 

Earthen  dams  are  largely  designed  according  to  empirical  rules, 
but  with  a  solid  material  such  as  masonry  it  is  possible  to  apply  to  a 
considerable  extent  the  principles  of  mechanics  in  determining  the 
proper  forms.  Moreover,  as  masonry  is  a  relatively  expensive 
material,  it  is  very  desirable  for  the  sake  of  economy  to  make  the 
theoretical  investigation  as  thorough  as  is  consistent  with  the  accuracy 
of  the  data. 

415.  The  External  Forces  Acting  upon  a  Dam — Dams  are  built  either 
straight  or  curved  in  plan.      In  the  former  case,  it  is  assumed  that  all 
forces  act  in  a  plane  perpendicular  to  the  dam,  and  that  the  dam  resists 
by  gravity  alone;  in  the  latter  case,  arch  action  may  exist  to  a  greater 
or  less  extent,  thus  involving  other  than  normal  forces.     The  first  case 

374 


FORCES  AND   STRESSES. 


375 


V 


only  will  be  here  treated,  and  it  will  be  sufficient  to  consider  a  length 
of  dam  of  one  unit.     (For  a  discussion  of  the  curved  form  see  Art. 

433-) 

The    principal    external    forces   acting   upon    an    impervious    dam, 
ABCD   (Fig.  87),   resting   upon   an    impervious    base  are,  the  water- 
pressure  P,  the  weight  of  the  masonry  6",  and  the 
reaction  R.     In  addition    to   these  forces,   certain 
others  require  consideration,  such  as  ice  and  wave 
pressure   near   the   top,    wind   pressure,  and    back 
pressure  of  water  on  the  side  BD.     Furthermore,  if 
the  dam  or  foundation  is  more  or  less  porous,  a  cer- 
tain amount  of  uplift  will  exist  to  reduce  the  effective 
weight  G,  as  shown  in  Art.  378.     However,  with 
good  mortar  joints  and  good  material  for  a  founda- 
tion this  uplift  will  be  very  small.     It  will  for  the  FlG-  87- 
present  be  neglected,  as  is  the  usual  practice,  but  this  and  the  other 
forces  mentioned  will  be  considered  later. 

Assuming  only  the  three  forces  P,  Gt  and  R  as  acting,  they  are 
all  readily  determined  for  any  given  section. 

416.  Internal  Stresses.  —  In  order  to  investigate  the  internal  stresses, 

pass  any  horizontal  section  mn 
through  the  dam  and  consider  the 
portion  ABEF  (Fig.  88).  Repre- 
sent here  the  external  forces  by  P 
and  G,  quantities  readily  determin- 
able  ;  and  the  internal  stresses  on  the 
section  which  are  necessary  for  equi- 
librium, by  the  two  components  V 
and  H.  The  resultant  of  all  vertical 
stresses  on  the  section,  tension  and 
compression,  is  thus  represented  by 
V,  and  H  is  the  resultant  shear. 

The    distribution  of   these 'direct  and  shearing  stresses  is  yet    to    be 

determined. 

417.  Ordinary  Assumptions  as  to  Stress  Distribution.  —  As  regards 
V  it  is  assumed,  first,  that  the  stress  varies  uniformly  across  the  sec- 
tion, as  in  the  ordinary  theory  of  beams,  retaining-walls,  etc.     If  e  is 
the  eccentricity  of  V  (distance  from  the  centre  of  EF),  the  stress  upon 
the  section  may  be  considered  as  due  to  a  compression  V,  uniformly 
distributed,  plus  a  stress  due  to  the  moment  Ve.     The  maximum  com 
pressive  stress  will  then  be  at  F,  and,  as  in  a  beam,  will  be  equal  to 


FIG.  83. 


376  MASONRY  DAMS. 

I 

V  t         6*\ 

•      (0 


At  E  the  stress  would  be  equal  to 

Vi         6e 


i  e\ 

/«!,,==  7(1  -Y}       ......     (2) 


So  long  as  e  is  less  than  g-,  or  the  resultant  V  remains  within  the 
middle  third  ^f  /,  compression  exists  at  all  points  and  the  distribution 
of  stress  is  as  represented  in  Fig.  (a).  If  e  =  g,  then  the  stress  at  E 

2V 
is  zero,  and  at  F  is  -^-,  or  double  the  average,  as  in  Fig.  (£).     If  e  is 

greater  than  g-,  then  by  the  formula  there  would  be  tension  at  E.     In 

masonry  structures  the  tensile  strength  is  not  to  be  relied  upon,  and  it 
is  therefore  assumed  that  there  is  no  tensile  stress.  The  distribution 
would  then  be  as  shown  in  Fig.  (<:),  and  the  entire  load  would  be 

carried  by  a  length  of  joint  equal  to  3? A     The  stress  at  F  would 

2V  V  f      4 

then  be  — = =       ' 


The  shear  H  is  not  usually  considered  except  as  requiring  a  sum", 
cient  frictional  resistance  along  the  plane  EF. 

418.  Errors  Arising  from  the  Ordinary  Assumptions. — There  are 
two  sources  of  error  in  the  above  method  of  treatment.  One  is  due  to 
the  assumption  that  the  maximum  intensity  of  stress  is  in  a  vertical 
direction.  It  will  really  be  inclined,  and  greater  than  as  above  figured, 
its  amount  and  direction  at  any  point  depending  upon  the  intensities 
of  V  and  H  at  that  point.  It  will  vary  from  the  vertical  direction  both 
on  account  of  the  inclination  of  the  resultant  of  Fand  H  (R),  and  on 
account  of  the  inclination  of  the  exterior  faces  of  the  dam.  At  the 
points  E  and  F  the  direction  of  the  maximum  compressive  stress  must 
be  parallel  to  the  respective  faces,  while  at  intermediate  points  it  will 
vary  between  the  two  extremes.  Even  were  the  material  homogeneous 
it  would  be  impossible  to  determine  these  compressive  stresses  and 
their  direction,  but  the  lines  of  maximum  pressures  would  probably  be 
somewhat  as  shown  in  Fig.  89, 


CONDITIONS   OF  STABILITY.  377 

To  allow  for  the  inclination  of  R  some  writers  use,  instead  of  F,  the 
force  R,  and  consider  it  as  acting  on  a  plane  equal  in  length  to  the 

V 
projection  of  EF  parallel  to  R.     This  is  equivalent  to  using  — —  in 

place  of  V  as  above,  where  a  is  the  angle  of  inclination  of  R  with  the 


FIG.  89.  FIG.  90. 

vertical.  This  assumes  that  the  resistance  of  the  masonry  is  due 
entirely  to  compressive  stress  on  the  inclined  surfaces  perpendicular 
to  R  (Fig.  90),  and  neglects  the  shearing  stress  on  the  other  surfaces. 
It  also  does  not  take  into  account  the  effect  of  the  inclined  faces  of 
the  dam  in  varying  the  direction  of  the  internal  stresses,  which  alone 
would  make  the  local  stresses  inclined  at  the  faces  even  though  the  re- 
sultant R  be  vertical.  The  most  common  method  of  treatment  is  to 
use  V  only,  and  to  allow  something  for  the  greater  intensities  of  stress 
in  an  inclined  direction  by  using  a  lower  working  intensity  for  the 
down-stream  face. 

The  other  error  in  the  ordinary  theory  is  the  assumption  that  the 
pressures  are  uniformly  varying.  For  a  section  like  a  high  masonry 
dam  the  greater  length  of  the  outside  toe  renders  that  portion  some- 
what more  elastic  than  the  other  part,  thus  tending  to  reduce  the  stresses 
at  this  point  and  to  increase  them  elsewhere.  Whatever  this  effect 
may  be,  it  is  on  the  side  of  safety. 

419.  Conditions  of  Stability. — Considering  any  section  EF,  as  in 
Fig.  88,  the  conditions  usually  imposed  to  secure  stability  are  three: 

(1)  The  maximum  compressive  stress  due  to  Fat  F  or  at  E  shall 
not  exceed  safe  limits. 

(2)  There  shall  be  no  tensile  stress  at  any  point  of  the  section. 
This  requires,  as  shown  in  Art.  417,  that  the  resultant  of  F  and  H  or 
of  P  and  G  shall  not  cut  the  section  outside  its  middle  third. 

(3)  The  resistance  to  shearing  or  sliding  shall  be  greater  than  the 
total  horizontal  force  at  the  level  of  the  joint. 

Another  condition  is  sometimes  stated  as  an  independent  one, 
namely,  that  the  dam  shall  not  overturn;  but  if  condition  (2)  is  met, 
there  can  be  no  possibility  of  overturning.  When  the  resultant  pres- 
sures for  reservoir  full  and  reservoir  empty  both  cut  the  edge  of  the 


MASONRY  DAMS. 

middle  third,  the  factor  against  overturning  is  2.  All  of  the  above 
conditions  must  be  fulfilled  at  the  foundation  as  well  as  at  all  sections 
of  the  structure,  and  if  the  foundation  material  is  less  strong  than  the 
masonry  of  the  dam  this  must  be  allowed  for  under  (i)  and  (3). 

Besides  these  conditions  of  stability  that  of  imperviousness  is  of 
course  understood,  although  this  requirement  is  not  absolute,  but 
merely  relative. 

420.  Resistance  to  Shearing  or  Sliding. — To  fail  by  sliding  on  a 
horizontal  joint,  or  a  succession  of  horizontal  and  vertical  joints,  the 
cohesion  of  the  mortar  must  be  overcome  as  well  as  the  friction.  The 
latter  is,  in  the  body  of  the  dam,  nearly  always  more  than  sufficient 
for  stability.  That  the  cohesion  of  the  mortar  is  also  to  be  largely 
counted  upon  is  shown  by  the  stability  of  numerous  concrete  dams, 
where  the  mortar  must  not  only  resist  shearing  on  a  horizontal  plane, 
but  on  planes  inclining  outwards  and  downwards,  on  which  the  intensity 
of  stress  is  much  greater  and  the  friction  much  less.  By  limiting  the 
compressive  stress  we  at  the  same  time  provide  for  shearing  stresses, 
and  they  need  not  be  further  considered. 

At  the  base  of  a  dam  the  sliding  tendency  must  be  well  looked 
after.  Where  the  foundation  is  clay,  or  perhaps  a  timber  platform, 
special  precautions  will  be  needed.  Table  No.  59  contains  coefficients 
of  friction  which  will  be  useful  in  this  connection.  They  are  from 
Baker,  Fanning,  and  others.  With  rock  foundations  the  conditions 
will  be  similar  to  those  in  the  body  of  the  structure  if  the  masonry  be 
well  bonded  to  the  bed-rock. 

TABLE   NO.  59. 

COEFFICIENTS    OF    FRICTION   OF   VARIOUS   MATERIALS. 

Material.  Coefficient, 

Granite  (roughly  worked)  on  gravel  and  sand  (wet) 0.41 

Pine  (sawed)  on  gravel  and  sand  (wet) 0.41 

Granite  (roughly  worked)  on  sand  (dry) ' 0.65 

"      "      (wet) 0.47 

Masonry,  on  clayey  gravel 0.577 

"  dry  clay 0.510 

"  moist  clay , 0.325 

Point-dressed  granite  (medium)  on  like  granite 0.70 

"  "    common  brickwork 0*63 

"    smooth  concrete 062 

Fine  cut  granite  (medium)  on  like  granite 0.58 

Dressed  hard  limestone  (medium)  on  like  limestone o  38 

"  "  "    brickwork 0.60 

Beton  blocks  (pressed)  on  like  Beton  blocks 0.66 

Common  bricks  on  common  bricks „ 0.64 

"  "        "    dressed  hard  limestone 0.60 


STABILITY   OF  LOW  DAMS. 


379 


421.  Allowable   Pressure. — This    will     depend    upon    the    kind    of 
masonry  adopted.     With  large  rubble  masonry,  as  ordinarily  employed, 
the  safe  pressures  are  taken  all  the  way  from  8  to  1 5   tons  per  square 
foot.     With  first-class  concrete  a  pressure  of  8  to  10  tons  may  be  used. 
Many  of  the  existing  high  dams  sustain  maximum  pressures  equal  to 
the  latter  figures,  and  several  exceed  14  tons.      The  Vyrnwy  Dam  has 
a  maximum    pressure   of  8.7   tons.      The   Quaker   Bridge   Dam    was 
designed  for  a  maximum  of  16.6  tons,  and  the  new  Croton  Dam  has 
practically  the  same  profile.      The  Periyar  Dam,  Madras,  of  concrete, 
sustains  8  tons.     The   San  Mateo  concrete  dam  sustains  a  pressure,' 
reservoir  full,  of  about  7.7  tons,  and  10  tons  with  reservoir  empty. 

422.  Weight  of  Masonry. — The  specific  gravity  of  rubble  masonry 
or  good  concrete  is  usually  taken  at  from  2j  to  2^,  corresponding  to 
weights  of  140  and  156  pounds  per  cubic  foot.      The  latter  value  was 
adopted  in    designing  the    Quaker  Bridge    Dam,   experiments  giving 
156.5    pounds.      In    the    Sweetwater    Dam    it  was   estimated   at    164 
pounds,    the   stone  being  very  dense    and  join'ts    narrow.      Concrete 
blocks  cut  out  of  the  Vyrnwy  Dam  had  a  specific  gravity  of  from  2.48 
to  2. 55. 

A.   Stability  of  Low  Dams. 

423.  Conditions  of  Stability. — Dams  up  to  30  or  40  feet  in  height 
are  usually  made  trapezoidal  in  form,  the  saving  obtained  by  making 
the   faces   curved   or   broken   not   being    enough   to  justify  the   extra 
trouble.      For  such  low  dams  the  only  condition  of  stability  requiring 
consideration,  besides  that  of  friction  on  the  base,  is  that  of  tension  in 
the  joints.      This  requires  that  the  resultant  pressure  shall  keep  within 
the  middle  third ;  for  economy,  it  should  just  cut  the  edge  of  the  middle 
third. 

424.  Calculation  of  Section. — Let  ABDC,  Fig.  91,  be  a  section  of 
a  trapezoidal  dam.     Let  the  dimensions  be  as  represented  in  the  figure. 
Further,    let  w  =  weight    of  a    unit    volume    of 

water,   and  w'  the  weight  of  a  unit  volume  of 
masonry.    Let  g  =  specific  gravity  of  the  masonry 

w' 
=  — .       The  components  of  the  water-pressure    ,£>    < 

are  Pv  and  Ph. 

For  dams  of  this  class  there  will  usually  be 
but  two  cases :  first,  when  the  front  face  BD  is 
vertical  or  nearly  so,  and,  second,  when  the  back 
face  AC  is  vertical,  or  is  given  a  definite  small 
batter.  In  the  first  case  n  is  assumed  and  /or  m  is  required ;  in  the 


30  MASONRY  DAMS. 

second  case  m  is  given  to  find  n  or  /.  The  problem  is  to  find  a  value 
of  /  such  that  the  resultant  of  P  and  G  will  just  cut  the  edge  of  the 
middle  third.  The  bottom  section  will  be  the  dangerous  one,  and  the 
only  case  to  be  considered  is  for  reservoir  full. 

It  is  assumed  for  safety  that  the  water  rises  to  the  top.     The  value 

of  P  then  equals  wA  C—  ;  its  point  of  application  is  —  above  the  base. 

The  value  of  G  can  readily  be  expressed  in  terms  of  w'  and  the  dimen- 
sions, and  its  line  of  action  found  by  rules  of  mechanics. 
We  have  then,  briefly, 


By  dividing  the  moment  about  D  of  the  several  partial  areas  of  the  sec 
tion  by  the  total  area,  we  find 


^  +  a        2an         n          am        mn 


Equating  now  to  zero  the  moments  of  Ph,  Pv,  and  G  about  the  outer 
edge  of  the  middle  third,  we  have,  for  stability, 


Substituting  in  this  equation  the  values  of  the  forces  given  above,  and 
the  value  of  d,  we  get  an  expression  containing  /,  m,  and  n\  but 
noting  that  /  =  a  +  m  +  n,  we  can  eliminate  either  n  or  m. 

w1 
We  thus  have  for  the  case  where  n  is  given,  putting  —  =  g, 


=\    }?-(a+nf(g-  i)  +  »»£•  +  _        .        .     (3) 

If  the  front  face  is  vertical,  n  =  o,  and  we  have 


/  =    Vhz  -  a\g  -  i) (4) 

For  the  second  case,  having  m  given,  we  derive  the  expression 


/  =    MA  +  B*  -  B, (5) 

in  which 

h*        m* 

A  =  a*  +  2am  +  —  -| , 

o  o 


STABILITY   OF  HIGH  DAMS.  381 

and 

If  the  back  face  is  vertical,  m  =  o,  and  we  have 

**+f''r    •  •  •  ^=4i  (6) 

h 

If  a  =  o,   eq.  (4)  gives  /  =  h,  and  eq.  (6)  /  =  -— —.      It  will  thus 

give  a  more  economical  design  to  have  the  back  face  vertical  or  nearly 
so,  rather  than  the  front  face.  The  latter  form  is,  however,  sometimes 
used  for  very  low  dams  where  designed  as  weirs,  or  where  built  in  con- 
nection with  such  weirs.  The  front  usually  has  then  a  batter  of  I  to  2 
inches  per  foot,  and  the  rear  whatever  is  necessary  to  give  stability. 

If  the  pressure  on  the  base  is  desired,  it  can  be  found  by  the  equa- 
tions of  Art.  417,  using  for  V  a  force  equal  to  the  resultant  of  G 
and  Pv.  The  force  tending  to  slide  the  dam  on  the  base  is  Pk.  The 
frictional  resistance  is  V  X  coefficient  of  friction.  If  a  section  should 
be  given  and  it  is  desired  to  investigate  its  stability,  the  value  of  the 
resultant  pressure  and  its  point  of  application  can  best  be  found  by 
graphics. 

B.    Stability  of  High  Dams. 

425.  General  Statement  of  the  Problem. — For  dams  exceeding  30  or 
40  feet  in  height,  it  is  economy  to  build  the  lower  face  in  the  form  of 
a  curve  or  broken  line.  In  designing  a  curved  profile  a  certain  height 
is  soon  reached,  when  it  becomes  necessary  to  investigate  the  stability 
of  the  dam  for  reservoir  empty,  and  at  a  still  greater  elevation  the  con- 
dition that  the  stress  shall  not  exceed  a  certain  maximum  value 
becomes  the  controlling  factor.  The  design  of  the  cross-section  is  there- 
fore a  somewhat  complicated  problem,  and  it  is  impossible  to  represent 
by  a  formula  a  profile  which  will  exactly  fulfil  all  the  conditions. 

Various  formulas  and  methods  of  designing  a  profile  have  been  pro- 
posed from  time  to  time,  differing  more  or  less,  but  most  of  them  based 
on  the  requirements  for  stability  enumerated  in  Art.  419.  Probably  as 
simple  a  method  as  any  is  that  adopted  by  Wegmann  as  the  result  of 
his  studies  for  the  Quaker  Bridge  Dam.  The  method  is  a  general  one 
and  will  be  here  briefly  stated,  and  the  working  equations  as  derived 
by  Wegmann  will  be  given.* 

*  For  a  full  discussion  of  the  subject  see  Wegmann's  "  Design  and  Construction 
of  Dams/'  New  York,  1907. 


382  MASONRY  DAMS. 

426.  Wegmann's  Method  of  Determining  the  Profile.  —  This  method 
consists  in  determining  at  successive  horizontal  sections,  beginning  at 
the  top,  the  necessary  width  of  section  to  fulfill  the  conditions  stated  in 
Art.  419,  assuming  the  area  enclosed  between  adjacent  sections  to  be 
trapezoidal.      In  this  way  by  taking  the  sections  sufficiently  close  the 
profile  may  be  determined  with  any  desired  degree  of  exactness. 

As  it  is  necessary  that  a  dam  shall  have  a  certain  top  width,  a,  the 
upper  portion  will  consist  of  a  rectangle  until  such  a  depth  is  reached 
as  to  bring  the  line  of  pressure  with  reservoir  full  at  the  outer  edge  of 
the  middle  third.  Below  this  point  the  down-stream  face  will  be 
battered  and  the  other  face  will  be  continued  vertically  downwards  until 
the  resultant  with  reservoir  empty  just  cuts  the  inner  edge  of  the  middle 
third.  The  inner  face  will  then  begin  to  receive  a  slight  batter. 
Finally,  a  depth  will  be  reached  below  which  the  length  of  the  joint 
will  be  determined  by  the  limiting  pressures  at  the  edges. 

The  water  is  assumed  to  rise  to  the  top  of  the  dam  in  order  to  pro-- 
vide  for  extreme  conditions.  Furthermore,  at  the  lower  sections  of 
the  dam,  where  the  back  face  becomes  slightly  inclined,  the  vertical 
component  of  the  water-pressure  is  neglected.  The  error  arising 
therefrom  is  slight  except  in  very  high  dams  and  where  the  allowable 
pressure  is  low,  and  is  on  the  side  of  safety. 

427.  The  calculation  of  the  profile  is  divided  into  five  different  stages, 
corresponding  to  the  different  sets  of  conditions  to  be  met. 

First  Stage.  —  Depth  of  rectangular  portion.     The  depth  at  which 
the  line  of  the  resultant  pressure  will  cut  the  edge  of  the  middle  third 
of  a  rectangle  may  be  found  by  making  /  =  a  in 
equation  (6),  page  381,  and  solving  for/£;  we 
get    - 

.....      (7) 


where  h  =  height  or  depth,  a  =  top  width,  and 
g  =  specific  gravity  of  the  masonry. 

Second  Stage.  —  The  back  to  be  continued 
vertical  and  the  front  battered.  The  section 
from  here  down  is  determined  by  considering 
successive  trapezoidal  blocks.  In  Fig.  92  let 
CDFE  be  such  a  trapezoidal  section  of  small 
thickness  //  situated  immediately  beneath  the 
FIG.  92.  portion  ABDC  already  designed,  which  portion 

may  be  of  any  form,  but  whose  weight,  area,  etc.,  are  known.     The 

following  notation  will  be  used: 


STABILITY  OF  HIGH  DAMS. 

W=  weight  of  portion  ABDC\ 

G  =  weight  of  portion  CDFE\ 
W  =  resultant  of  Wand  G; 

A  =  area  of  ABDC\ 
,4  '  =  area  of  CDFE\ 

m  =  distance  of  line  of  action  of  Wfrom  C\ 

n  —  distance  of  line  of  action  of  W  from  E\ 

I—  length  of  joint  CD\ 

x  —  required  length  of  joint  EF; 

y  =  batter  of  CE  ; 

h  =  thickness  of  section  ; 

d  =  depth  of  water  at  E  =  height  of  dam  above  this  point; 

/  =  limiting  intensity  of  pressure  at  F\ 

q  =  limiting  intensity  of  pressure  at  £,  usually  greater  than/; 
w  —  weight  of  a  cubic  unit  of  water  ; 
w'  =  weight  of  a  cubic  unit  of  masonry; 

w' 
g  =  specific  gravity  of  masonry  =  —  . 

The  value  of  x,  then,  so  long  as  CE  can  be  made  vertical,  is  given 
by  the  equation 

x  =  VB  +  C*  -  C,   .......     (8) 


in  which  *  =       +  +  /*,     and     C-- 

The  value  of  n  is  given  by  the  equation 

(          tx       /2  Am 


A+A> 


Equation  (8)  can  be  used  so  long  as  n  is  greater  than  —  . 

In  treating  the  next  trapezoidal  section  the  portion  ABFE  is  now 
the  known  portion,  the  various  properties  of  which  are  to  be  substituted 
for  like  properties  of  ABDC  in  the  above  equations.  Thus  the  new 
value  of  m  is  ;/  of  eq.  (9),  etc. 

Third  Stage.  —  For  the  next  series  of  courses  the  face  CE  must  be 

battered  so  that  n  shall  always  be  equal  to  —  .      The  value  of  x  is  given 
by  the  equation 


384  MASONRY  DAMS. 

and  the  value  of  y  is 


_  2A(x  —  3»g)  —  hi* 
6A  +  h(2l  +  *y 

Fourth  Stage.  —  When  by  the  use  of  (10)  and  (n)  the  value  of  the 
pressure  on  the  front  face  would  exceed  /,  the  formula  is 


W3 
x  = 


This  value  of  x  is  to  be  used  as  soon  as  it  becomes  larger  than  the 
value  given  by  (10).      The  batter  is  still  given  by  (n);  also,  n  —  —  . 

Fifth  Stage.  —  When  the  pressure  on  the  back  face  becomes  equal 
to  q,  then  the  formula  is 

X  =  VD  +  E*+E,    .  '.;.:,'.'   .    .    .   (13) 

ik 

I  d*  ~T~~2 

in  which  /?  =  —  .-          -  ,     and     E  =  -  -  ,  and  the  batter  i::. 


w  w 


A(4*-  6m)  +  lh(x  _  /)  +  Ah  -  -t  ) 

\  uU    I  ,         . 

y  ''  6  A  ~~ 


Equation  (13)  is  to  be  used  when  it  gives  a  value  of  x  greater  than  that 

9 

found  by  eq.  (12).      For  this  case,  n  =  \x  -  |  •  W^J^_  A^ 

The  foregoing  equations  are  all  that  are  needed  in  designing  the 
profile  of  any  high  dam.  In  fact  equations  (12),  (13),  and  (14)  will 
not  be  used  until  a  height  of  100  feet  or  more  is  reached,  depending 
upon  the  assumed  values  of/  and  q. 

Graphical  methods  of  determining  lines  of  pressures,  and  of  check- 
ing the  results  found  by  algebraic  processes,  will  readily  suggest  them- 
selves to  the  student. 

428.  Effect  of  Approximations  in  the  Foregoing  Treatment.  —  The 
effect  of  neglecting  the  vertical  component  of  the  water-pressure  on  the 
inclined  upper  face  is  very  small  until  the  height  becomes  very  great. 
Then  this  additional  component  acts  to  throw  the  resultant  nearer  the 
upper  face  and  therefore  to  increase  the  press.ures  near  this  face  and  to 
decrease  those  near  the  lower  face.  In.  the  last  respect  it  tends  to 
compensate  for  the  error  due  to  considering  vertical  forces  only.  The 
effect  is  greater  the  lower  the  allowable  pressure  intensities. 


STABILITY  OF  HIGH  DAMS. 


3*5 


The  effect  of  neglecting  the  inclination  of  the  resultant  pressure  on 
any  section  is  of  course  to  derive  a  pressure  less  than  the  actual.  To 
take  account  of  this  where  the  pressure  determines  the  profile,  the  value 
of/  in  eqs.  (12)  and  (13)  may  be  reduced  in  the  ratio  of  cos2  a  to  I,  a 
being  the  inclination  of  the  resultant  with  the  vertical.  The  value  of 
/  can  thus  be  readily  varied  to  accord  with  the  change  in  a  as  the 
design  proceeds.  By  making  /  constant  and  somewhat  lower  than  q, 
as  is  done  by  Wegmann,  the  effect  of  inclined  resultant  can  be  approxi- 
mately allowed  for. 

429.  Use  of  a  Standard  Profile. — Fig.  93  represents  Wegmann 's 
"  practical  profile  No.  2,"  constructed  for  a  dam  100  feet  high  without 
reference  to  pressures  and  with  some 
simplification  of  the  theoretical  out- 
line. The  value  assumed  for  g  was 
2^-,  corresponding  to  a  weight  of 
masonry  of  145.8  pounds  per  cubic 
foot.  Such  a  section  when  once  cal- 
culated can  be  used  for  any  height  of 
dam  so  long  as  the  safe  pressures  are 
not  exceeded,  by  simply  cutting  off  a 
dam  of  the  desired  height  from  the 
standard  section,  or  by  changing  all 
the  dimensions  proportionately,  or  by 
both  processes,  as  may  be  necessary 
to  secure  the  required  top  width.  If 
the  safe  pressures  are  exceeded,  eqs. 

(12),  (13),   and  (14)  will  have  to  be      \—  66./I 

made  use  of  for  the  lower  sections.  FIG.  93. 

If,  for  example,  a  profile  is  required  for  a  dam  50  feet  high  and  with 
8  feet  top  width,  proceed  as  follows:  Get  by  proportion,  from  Fig.  93, 
a  profile  with  top  width  8  feet  and  height  80  feet,  and  then  use  the 
upper  50  feet  of  such  profile.  For  masonry  with  a  different  specific 
gravity  a  new  standard  profile  would  have  to  be  calculated. 

The  pressures  at  the  various  depths  for  the  profile  of  Fig.  93  are 
given  in  Table  No.  60,  the  data  for  which  are  from  Wegmann.  In 
dams  of  other  heights  but  in  which  the  dimensions  are  proportional,  the 
pressures  will  also  be  proportional.  Thus  in  a  dam  120  feet  high, 
made  similar  to  Fig.  93  (top  width  12  feet,  bottom  width  =  66. 1 1  X 

—  =  79-332  feet),  the  pressure  at  the  bottom  will  be  7.16  X  - —  = 
8.92  tons.     At  a  point  80  feet  below  the  top  the  pressure  will  be  pro- 


386 


MASONRY  DAMS. 


portional  to  that  given  for  the  loo-foot  dam  at  a  point  =  -  -  x  100  = 

66.7  feet  from  the  top,  —  4.9  x  -    -  =  5-88  tons  per  square  foot.     For 

i  oo 

a  dam  150  feet  high  the  maximum  pressure  is  7. 16  X  1.5  —  10.74  tons 
per  square  foot.  With  safe  values  of  8  to  10  tons  per  square  foot  as 
commonly  used  it  is  seen  that  a  standard  profile  such  as  here  given 
would  be  suitable  for  dams  up  to  about  150  feet  in  height. 

TABLE    NO.  60. 

PRESSURES    FOR   WEGMANN's    PRACTICAL    PROFILE    NO.    2.      (FlG.  93.) 


Pressures  in  Tons  per  Sq.  Foot. 

Pressures  in  Tons  per  Sq.  Foot. 

Distance  from 
Top  of  Dam  in 
Feet. 

Down-stream 
Face, 
Reservoir  Full. 

Up-stream  Face, 
Reservoir  Empty 

Distance  from 
Top  of  Dam  in 
Feet. 

Down-stream 
Face, 
Reservoir  Full. 

Up-stream  Face, 
Reservoir  Empty 

9-372 

0.95 

0.68 

60 

4-45 

4-35 

15 

1.84 

1.69 

65 

4.78 

4-73 

2O 

2.52 

1.77 

70 

5-" 

5-ii 

25.983 

2-77 

2-45 

75 

5-45 

5.48 

30 

2.80 

2.82 

80 

5-78 

5-86 

35 

2.97 

3.06 

85 

6.13 

6.22 

40 

3-23 

3-30 

90 

6.48 

6.59 

45 

3-51 

3-55 

95 

6.82 

6.96 

50 

3-8i 

3.81 

100 

7.16 

7-33 

55 

4-13 

4.08 

\r 


430.  Approximate  Triangular  Profile. — A  profile  very  closely  ap- 
proximating the  type  illustrated  in  Fig.  93  can  be  quickly  determined 
from  any  assumed  data  as  follows:  Assume  first  the 
triangular  profile  ABC,  Fig.  94,  with  vertical  back 
face.  For  reservoir  full  the  value  of  x  is  given  by 
eq.  (6),  page  381,  by  putting  a  —  o  and  replacing  / 

and  h  by   x  and  d  respectively.       It  is  x  =  — ^_. 

t/£- 

This  value  is  proportional  to  d  and  hence  the  line 
of  pressure,  reservoir  full,  cuts  the  outer  edge  of  the 
f  middle  third  at  all  sections.      For  reservoir  empty 
FIG.  94.  tne  resultant  evidently  cuts  the  inside  edge  of  the 

middle  third  at  all  points,  so  that  until  a  depth  is 
reached  where  the  allowable  pressures  are  exceeded  the  triangle  exactly 
satisfies  the  conditions  of  stability  and  is  the  most  economical  form.  A 
zero  top  width  is,  however,  impracticable,  and  to  get  a  practical  profile 
the  block  AFK  of  width  a  is  added.  The  effect  of  this  block  is  slightly 
to  disturb  the  positions  of  the  pressure  lines,  but  for  high  dams  the 


STABILITY   OF  HIGH  DAMS.  367 

variation  is  so  small  as  to  be  negligible.  The  line  of  pressure,  reser- 
voir full,  is  brought  slightly  within  the  middle  third,  while  that  for 
reservoir  empty  passes  a  very  little  outside.  Such  a  profile,  rounded 
off  slightly  at  the  point  K,  can  therefore  be  used  with  practical  exact- 
ness for  dams  of  such  height  that  the  pressures  need  not  be  considered. 
If  more  exact  methods  are  desired,  this  form  may  be  used  for  preliminary 
plans.  It  also  affords  a  ready  check  on  more  elaborate  determinations. 
The  maximum  pressure  intensity,  /,  of  the  triangular  profile  is 

equal  to  —  =  w'd.     For  a  value  of  w  =  145.8  and  d  =  150,  /  = 

10.93  tons  per  square  foot  as  compared  to  10.74  tons  for  the  profile  of 
Fig.  93.     The  coefficient  of  friction  necessary  for  stability  against  slid- 

P          I 

ing  is  equal  to  -^  =  —-=.  =  .65  for  a  value  of  g  =  2\. 

431.  Forces  not  Considered  in  the  Preceding  Analysis. — As  already 
remarked,  the  upward  pressure  of  the  water  is  usually  neglected.  In 
one  dam  built  recently,  the  Gileppe  Dam,  154  feet  high,  this  action 
was  allowed  for,  resulting  in  a  greatly  increased  section ;  but  the  con- 
tinued stability  of  many  high  dams  in  which  this  element  is  neglected 
indicates  that  it  need  not  be  taken  into  account. 

It  has  been  shown  that  with  good  mortar  joints  and  good  connec- 
tion with  bed-rock  the  uplift  cannot  possibly  be  more  than  a  few  pounds 
per  cubic  foot.  For  small  areas  near  crevices  where  springs  occur  it 
might  be  very  considerable,  but  such  areas  would  in  any  case  be  but  a 
small  fraction  of  the  whole.  A  system  of  drains  such  as  used  in  the 
Vyrnwy  Dam,  page  405,  would  avoid  all  possibility  of  such  action 
beyond  that  due  to  the  head  of  water  on  the  lower  face.  A  dam 
founded  on  a  loose  porous  foundation  would  of  course  be  differently 
conditioned,  but  such  would  scarcely  be  a  masonry  dam. 

There  is  usually  .a  certain  depth  of  water  on  the  lower  face.  The 
pressure  of  this  should  be  taken  into  account  when  this  part  of  the 
section  is  reached  ;  also  any  considerable  unbalanced  earth-pressure. 

Wind-pressure,  reservoir  empty,  will  add  slightly  to  the  stresses, 
but  the  amount  is  not  sufficient  to  be  considered.  Wave  action  will 
add  something  to  the  pressure  of  the  water,  but  this  may  be  considered 
as  amply  provided  for  in  assuming  the  water-level  at  the  top  of  the 
dam. 

The  pressure  of  ice  is  sometimes  very  great,  but  what  allowance 
should  be  made  for  this  is  impossible  to  say.  The  maximum  pressure 
would  be  measured  by  the  crushing  strength  of  ice,  which  may  be  taken 
at  about  400  pounds  per  square  inch.  Such  great  pressures  would 


388  MASONRY  DAMS. 

doubtless  seldom  occur,  but  may  be  approached  in  confined  locations 
for  either  a  high  or  a  low  dam.*  The  pressures  due  to  ice  moved  by 
the  wind  in  the  spring  would  be  very  much  less  and  would  correspond 
to  a  strength  of  ice  of  probably  not  over  30  or  40  pounds  per  square 
inch,  perhaps  4000  or  5000  pounds  per  lineal  foot  for  ordinary  cases. 
In  the  case  of  the  Quaker  Bridge  Dam  it  was  the  opinion  of  the 
board  of  experts  that  ice-pressure  should  be  taken  at  43,000  pounds 
per  lineal  foot.  The  effect  of  such  a  force  can  be  taken  account  of  by 
combining  it  with  the  horizontal  pressure  of  the  water.  Usually  a  suffi- 
cient margin  of  strength  to  resist  ice-pressure  will  be  afforded  by  the 
mass  of  masonry  above  high-water  line  dimensioned  according  to 
empirical  rules  of  practice. 

432.  Top  Width  and  Height  above  Water-line. — If  the  dam  is  to  be 
used  as  a  driveway,  the  top  width  will  have  to  be  at  least  8  feet  besides 
width  of  parapets.  Otherwise  the  width  and  height  above  high-water 
line  must  be  such  as  to  secure  stability  against  wave  and  ice  action  as 
just  noted,  and  to  prevent  waves  from  washing  over  the  top.  A  formula 
for  height  of  waves  was  given  in  the  previous  chapter  (page  352).  In 
practice  the  width  varies  from  a  minimum  of  4  to  5  feet  for  low  dams 
to  15  or  20  feet  for  very  high  dams;  and  the  height  above  high- water 
line  from  2  or  3  feet  to  about  10  feet.  In  some  cases  much  larger 
dimensions  may  be  required  for  low  dams  than  those  given . 

433 •  Curved  Dams. — Arch  Action  alone  Considered. — Up  to  this 
point  it  has  been  assumed  that  a  dam  resists  overturning  by  gravity 
action  alone.  Obviously  if  a  short  dam  be  built  with  a  sharp  curvature 
convex  up-stream,  with  its  flanks  resting  against  rigid  supports,  over- 
turning will  also  be  resisted  by  arch  action.  In  investigating  the 
stresses  of  such  a  dam  it  may  be  looked  upon  as  a  section  of  a  circular 
open  well  constructed  in  the  middle  of  a  reservoir.  Omitting  any 
resistance  by  gravity  action  and  assuming  each  horizontal  lamina  to 
support  the  water-pressure  against  itself  independently  of  the  others, 
the  horizontal  compressive  stress  in  a  lamina  I  foot  thick  will  be  equal 
to  wdr,  where  w  =  weight  of  water,  d  =  depth  of  lamina  below  water- 
surface,  and  r  —  radius  of  curvature  of  the  dam.  If  this  pressure  be 
assumed  as  uniformly  distributed  over  the  cross-section  of  the  lamina, 

the  pressure  per  square  foot  will  then  be  equal  to  /  =  — — - ,  where  t  — 
thickness  of  wall  at  the  depth  d.  For  a  constant  value  of/  the  thick- 

*  For  account  of  failure  of  a  dam  at  Minneapolis  by  ice-pressure,  see  Eng.  News, 
1899,  XLI.  p.  307. 


STABILITY  OF  HIGH  DAMS.  389 

ness   /  should  vary  with  d,  thus  giving  a  triangular  profile    in  which 

r 


p  =10  tons  =  20,000*  pounds,  we  have  t  = 

p  20,000 

=  .03  1  dr.     The  value  of  t  for  a  gravity  dam    with  triangular  profile 
was  shown  to  be  equal  to—-'     Putting  £•  =  2j,  this  becomes  t  =  ,66  d. 


Theoretically,  therefore,  the  two  sections  would    be  equal  when   r  = 

-  -  =  213  feet.     This  rough  calculation  indicates  that  the  only  situa- 
.0031 

tion  where  a  purely  arch  type  can  be  economically  considered  is  in  a 
very  narrow  alley. 

434.  Gravity  and  Arch  Action.  —  A  curved  dam  with  its  base 
securely  fastened  to  the  foundation  cannot  wholly  fail  to  resist  by 
gravity.  A  gravity  dam  may  be  looked  upon  as  a  vertical  cantilever 
beam  which  when  loaded  will  deflect  until  certain  internal  stresses  are 
developed  sufficient  to  resist  the  load.  (The  vertical  force  of  gravity 
produces  a  longitudinal  compression  in  this  beam  and  prevents  any  of 
the  stresses  from  becoming  tensile).  If  such  a  dam  be  now  curved  in 
plan,  the  downward  deflection  of  the  top  will  also  be  resisted  by  the 
circumferential  stresses  or  arch  action.  The  relative  amounts  of  beam 
and  arch  action  will  be  proportional  to  the  rigidity  of  the  two  paths 
over  which  the  load  passes.  Thus  a  massive  dam  of  long  radius  would 
be  very  much  more  rigid  as  a  beam  than  as  an  arch,  and  the  arch 
action  would  therefore  be  very  small.  On  the  other  hand  a  thin  wall 
of  short  radius  would  be,  especially  towards  the  top,  of  relatively  great 
flexibility  as  a  beam,  and  such  would  be  mostly  supported  by  arch 
action.  No  curved  dam  will  therefore  resist  wholly  by  arch  action, 
nor  by  gravity  or  beam  action. 

It  would  theoretically  be  possible,  by  taking  account  of  both  actions, 
to  design  a  curved  dam  section  that  would  be  less  in  area  than  either 
the  gravity  or  the  arch  dam.  However,  the  variation  in  length  of  dam 
from  top  to  bottom,  the  variation  in  thickness  and  in  the  elasticity  in 
different  directions  due  to  differences  in  compactness,  are  some  of  the 
elements  that  make  the  problem  too  uncertain  and  complicated  to  admit 
of  this  being  readily  done. 

The  Lake  Cheeseman  Dam,  Colorado,  is  designed  as  a  gravity  dam 
with  curved  plan,  the  radius  of  curvature  being  400  feet  and  the  total 
height  225  feet,  the  lower  60  feet  being  in  a  very  narrow  gorge.  Cal- 
culations of  the  relative  amounts  of  gravity  and  arch  actions,  made  by 


390 


MASONRY  DAMS. 


Mr.  S.  H.  Woodard,  assuming  for  this  purpose  a  height  of  165  feet,  gave 
results  as  follows  :  * 


Depth  below  Top. 

Percentage  of 
Gravity  Action. 

Percentage  of 

Arch  Action. 

15  feet. 

I; 

i35    " 

53 
90 

94 
97 
9Q.8 

47 
IO 

6 
3 

O.2 

435.  Methods  Followed  in  Practice.  —  In  practice  there  are  three 
methods  followed  :  ( i )  to  make  the  dam  straight  and  therefore  a  gravity 
dam  ;  (2)  to  give  the  dam  a  sharp  curvature  when  conditions  will  per- 
mit, and  rely  more  or  less  on  arch  action  ;  and  (3)  to  build  a  gravity 
dam  in  a  curve,  and  consider  any  arch  action  as  an  additional  element 


FIG.  95.  —  BEAR  VALLEY  DAM.  FIG.  96.  —  SWEETWATER  DAM. 

of  safety.  In  the  case  of  moderately  short  dams  the  third  method  is 
considered  preferable  by  most  engineers.  For  long  dams,  however, 
the  advantage  gained  by  using  a  curved  plan  of  long  radius  would  be 
very  slight  and  not  commensurate  with  the  extra  trouble  and  expense 
involved.  For  very  short  dams  where  radii  of  200  or  300  feet  can  be 
used  the  second  method  may  be  employed.  It  is  to  be  noted  that  in 
the  bottom  of  a  narrow  valley  where  the  thickness  of  a  gravity  dam  is 
perhaps  greater  than  its  length,  arch  action  may  take  place  even  in  a 
straight  dam. 

436.  Examples.  —  A  few  dams  have  been  built  in  which  the  section  is 
materially  less  than  that  required  for  gravity.  The  boldest  of  these  is  the 

*  For  discussion  of  this  subject  and  methods  of  calculation  see  paper  on  Lake 
Cheeseman  Dam  in  Trans.  Am.  Soc.  C.  E.,  1904,  LIII.  p.  89.  The  discussion  con- 
tains descriptions  and  calculations  for  a  unique  arch,  or  "  dome,"  type  of  dam  at 
Ithaca,  N.  Y 


STABILITY  OF  HIGH  DAMS. 


391 


Bear  Valley  Dam  of  California,  illustrated  in  Fig.  95.  The  radius  of  the  top 
is  about  250  feet.  It  is  built  of  un coursed  rubble.  If  it  be  assumed  to  act 
as  a  gravity  dam,  the  resultant  pressure  would  pass  many  feet  outside  the  base. 
Calculated  as  an  arch  dam  the  pressures  near  the  base  are  40  tons  or  more 
per  square  foot.  Another  dam  of  this  type  is  the  Zola  Dam  in  France.  It  is 
123  feet  high  and  41.8  feet  thick  at  the  base  and  has  a  radius  of  curvature  of 
158  feet. 

The  Sweetwater  Dam  of  California  may  also  be  considered  of  this  type, 
although  designed  as  a  gravity  dam  (Fig.  96).  Assumed  as  such,  the  line  of 
pressure  falls  at  about  the  middle  of  the  outside  third.  It  has  a  radius  of 
curvature  of  222  feet  and  undoubtedly  acts  partly  as  an  arch.  In  1895  it  was 
overtopped  for  40  hours  by  a  high  flood  without  injury,  the  water  standing 
22  inches  above  the  parapet.  It  is  built  of  uncoursed  rubble,  great  care 
having  been  taken  in  executing  the  work.  The  masonry  weighs  about  164 
pounds  per  cubic  foot.* 

The  Barossa  Dam  in  South  Australia  is  a  modern  example  of  the  arch  type 
of  dam.  It  is  shown  in  section  in  Fig.  96a.  The  radius  of  the  dam  is  200 
feet.  By  substituting  this  type  for  the  gravity  type  a  saving  of  about  50  per 


FIG.  96a.  — BAROSSA  DAM. 

cent  of  the  estimated  cost  was  effected.  Rubble  concrete  was  employed  in  its 
construction.  In  the  upper  part  of  the  dam  several  horizontal  rows  of  4o-lb. 
steel  rails  were  inserted  to  add  strength  and  rigidity.  Observations  regard- 
ing movements,  due  to  temperature  changes,  showed  a  movement  of  J  inch  of 
the  top,  resulting  from  a  change  of  50°  F.f 

Another  very  bold  arch  dam  is  the  Upper  Otay  Dam  of  the  Southern 
California  Mountain  Water  Co.  Its  maximum  height  is  84  feet  and  width  of 
base  14  feet.  The  radius  of  curvature  is  359  feet.  It  is  of  concrete,  rein- 
forced partly  with  steel  cables  and  partly  with  steel  plates.  $ 

*  Trans.  Am.  Soc.  C.  E.,  1888,  xix.  p.  201. 

t  Eng.  News,  1904,  LI.  p.  321. 

J  Ibid.  p.  326;  Eng.  Record,  Nov.  1903,  p.  590. 


392  MASONRY  DAMS. 

CONSTRUCTION. 

437.  The  Foundation. — For  large  dams  the  foundation  should  be 
solid  rock.  In  preparing  the  foundation  surface  all  loose  and  partially 
decomposed  material  should  be  excavated  until  a  firm  base  is  reached. 
If  the  bottom  is  smooth  it  should  be  roughened  by  excavating  shallow 
cavities  in  the  rock.  At  points  where  crevices  occur  the  excavation 
must  be  carried  down  to  a  solid  bottom  and  all  loose  material  must  be 
removed.  After  an  acceptable  surface  is  reached  it  should  be 
thoroughly  washed  or  scrubbed  with  water  in  order  that  there  may  be 
a  secure  bond  between  the  foundation  and  the  masonry.  Many 
engineers  follow  the  practice  of  coating  the  prepared  foundation  with  a 
layer  of  neat  cement.  The  great  care  necessary  in  this  part  of  the 
work  is  illustrated  by  the  following  specification  relating  to  the  con- 
struction of  the  concrete  dam  at  Butte,  Mont.,  Chester  B.  Davis,  Mem. 
Am.  Soc.  C.  E.,  engineer: 

44  Whenever  the  slope  of  the  solid  bed-rock  of  the  dam-site  makes 
a  greater  angle  than  5°  with  the  horizontal  it  must  be  rough-stepped 
by  removing  the  least  amount  possible  of  bed-rock.  Where  the  rock 
beneath  the  dam  is  smooth  and  free  from  cross-seams  it  must  be  made 
rough  either  by  stepping  or  blasting  holes  with  a  superficial  area  of  from 
6  to  1 2  feet  and  a  depth  of  from  I  to  3  feet. 

4 'Each  square  foot  of  the  natural  bed-rock  beneath  the  proposed 
structure,  and  to  include  an  area  to  an  elevation  of  20  feet  above  the 
flow-line,  and  for  at  least  200  feet  above  and  100  feet  below  the  upper 
and  lower  toes  of  the  dam,  must  be  carefully  examined  and  everything 
not  natural,  true,  and  perfectly  solid  granite  rock  over  this  area  be 
removed. 

44  Each  crevice,  joint,  or  other  opening  beneath  the  structure  must 
be  examined  and  tested  and  all  material  removed  which  would  be 
started  or  stirred  by  a  pressure  up  to  at  least  the  maximum  load  on  the 
base  or  abutments,  or  by  a  minimum  strain  of  25  tons  per  square  foot. 
Each  crevice,  joint,  crack,  or  other  opening  must  be  filled  with  granite 
or  concrete  after  completing  the  blasting  for  the  portion  of  the  dam 
where  located.  Openings  outside  the  limits  of  the  structure  must  be 
filled  flush  with  the  surface  and  rammed  where  possible  until  perfectly 
compact.  Openings  beneath  the  dam  must  be  treated  in  the  same 
manner,  unless  large  enough  to  be  properly  filled  with  the  concrete 
used  for  the  base  of  the  dam.  In  all  cases  these  openings  must  first 
be  grouted."  * 

*  Eng.  News,  1892,  xxvin.  p.  554. 


CONSTRUCTION. 


393 


In  building  large  dams  the  excavation  for  the  foundation  becomes 
a  matter  of  considerable  difficulty,  especially  where  a  great  depth  of 
earth  overlies  the  rock.  The  excavation  in  such  a  case  becomes  very 
broad,  and  as  a  consequence  is  usually  made  with  such  slopes  as  to  be 
self-supporting,  no  attempt  being  made  to  use  bracing.  Ample  pump- 
ing capacity  is  here  a  prime  requisite.  At  the  New  Croton  Dam  the 
foundation  was  1300  by  500  feet  by  130  feet  deep.  The  stream  was 
diverted  by  means  of  a  temporary  channel  and  large  wing  dams  con- 
structed above  and  below  the  excavation. 

438.  Earth  Foundations. — Low  dams  of  masonry  are  quite  often 
founded  on  hard  clay  or  even  compact  sand,  a  construction  often  made 
necessary  where  waste-weirs  are  placed  in  earthen  embankments.  In 
building  upon  such  foundations  great  care  must  be  observed  to  avoid 
overloading  the  material  and  to  prevent  seepage  under  the  dam.  Plank 
foundations  are  very  commonly  used  to  aid  in  distributing  the  load, 
and  sheet-piling  driven  well  into  the  foundation  at  the  upper  edge  of  the 
dam  is  of  great  value  in  reducing  seepage. 

A  good  example  of  a  dam  built  on  earth  foundation  is  the  one  at 
Southington,  Conn.,  shown  in  Fig.  97.  In  the  construction  of  this 


FIG.  97.— SOUTHINGTON  DAM. 

dam  the  bed  of  the  stream,  which  was  a  very  fine  quicksand,  was  pre- 
pared by  excavating  two  trenches  parallel  to  the  face  of  the  dam  and 
of  a  depth  of  about  3  feet.  Sills  were  laid  at  the  bottom  and  the  top 
of  the  excavation,  and  sheet-piling  driven  and  spiked  to  them.  The 
trenches  were  then  filled  with  concrete  and  the  entire  foundation 
covered  with  a  layer  of  concrete  I  foot  thick  by  I  5  feet  wide.  The 
dam  is  built  of  granite  rubble.*  (See  also  description  of  Dunning 's 
Dam,  page  403.) 

*  Trans.  Am.  Soc.  C.  E.,  1886,  xv.  p.  887. 


394  MASONRY  DAMS. 

439.  Percolation  of  Water  beneath  the  Dam. — It  is  quite  frequently 
the  case  that  considerable  trouble  is  experienced  from  water  seeping 
through  at  the  foundation  surface  and  appearing  in  the  form  of  large 
or  small  springs.    In  handling  these  springs  the  same  general  methods 
are  used  as  described  for  earthen  dams.      Great  care  must  be  taken  to 
avoid  water-pressure  existing  over  any  considerable  area  of  the  bottom 
of  the  dam,  as  such  pressure  is  usually  assumed  not  to  exist.      The 
great  importance   of  this   matter  is  apparent  when  we  consider  the 
excessive  section  used  in  the  Gileppe  Dam  where  full  water-pressure 
was  provided  for.     The  failure  of  the  Bouzey  Dam  is  attributed  to  water 
getting  into   cracks  caused  by  tension  in  the  masonry  due  to  a  too 
narrow  section. 

If  the  water  is  present  in  large  quantities,  the  most  certain  way  of 
avoiding  upward  pressure  is  to  lead  the  water  out  to  the  lower  face  of 
the  dam,  as  was  done  for  the  Vyrnwy  Dam.  A  French  engineer^ 
Maurice  L£vy,  has  suggested  the  construction  of  a  guard-wall  in  front 
of  the  dam  and  connected  therewith  by  means  of  short  buttresses.  By 
this  arrangement  any  water  percolating  through  the  wall  could  be 
readily  drained  out  from  the  spaces  between  wall  and  dam.  Percola- 
tion and  resulting  pressures  are  to  some  extent  avoided  by  making  the 
dam  itself  as  impervious  as  possible,  and  also  the  foundation  for  some 
distance  above  the  upper  face  of  the  dam.* 

In  preparing  the  foundation  of  the  New  Croton  Dam  the  greatest 
care  was  exercised  in  removing  all  unsound  material  and  in  building 
over  springs  of  water  in  such  a  way  as  to  avoid  as  far  as  possible  all 
upward  pressure.  The  rock  foundation  was  carefully  scrubbed  and  all 
erosions  and  cracks  were  traced  out  by  drilling  numerous  holes  in  their 
vicinity.  Such  cracks  were  usually  piped  and  rilled  with  grout  forced 
in  under  pressure.  Where  a  flow  of  water  was  encountered  pipes  were 
also  led  to  an  adjacent  drain  or  sump  and  the  water  permitted  to  escape 
until  the  masonry  had  been  built  up  for  some  distance.  The  pipes 
were  then  filled  with  grout.  For  a  detailed  description  of  this  impor- 
tant work,  see  paper  by  C.  S.  Gowan  in  Trans.  Am.  Soc.  C.  E.,  1900, 
XLIII.  page  469. 

440.  Construction  of  the  Masonry. — Uncoursed  rubble  or  concrete 
is  usually  employed  in  dam  construction.      The  object  to  be  attained 
is  to  secure  a  homogeneous  structure,  free  from  all  through  joints  or 
weak  places  of  separation.      Concrete,  well  placed,  is  in  this  respect 
an  ideal  material.     Rubble  masonry,  in  which  all  joints  are  thoroughly 

*  Mr.  Freeman  in  his  report  on  New  York's  Water-supply  suggests  the  use  of  a 
thin  sheet  of  lead  placed  vertically  in  the  masonry  a  few  feet  back  of  the  face. 


CONS  TR  UC  TION. 


395 


filled  with  mortar,  and  larger  spaces  with  concrete,  has  been  used  for 
most  of  the  high  dams.  It  is  in  fact  a  rubble  concrete  where  the 
mortar  is  reduced  to  as  small  a  proportion  as  possible.  The  material 
to  be  adopted  in  any  case  will  be  determined  largely  by  the  question 
of  expense. 

Rubble  is  often  faced  with  broken-range  ashlar.  This  adds  strength 
to  the  face,  but  is  objected  to  on  the  ground  of  its  greater  rigidity  and 
therefore  its  tendency  in  settling  to  separate  from  the  rubble  backing. 
Such  facing  should  be  well  bonded  to  the  body  of  the  structure. 
Several  recent  important  dams,  among  which  are  the  Nashua  Dam  and 
the  New  Croton  Dam,  have  ashlar  facing.  In  the  Croton  Dam  the 
facing  courses  vary  in  size  from  30  to  15  inches.  The  joints  are  not  to 
exceed  £  inch  for  4  inches  from  the  face.  In  each  course  every  third 
stone  is  to  be  a  header,  with  a  length  of  at  least  4  feet.  The  stretchers 
are  to  be  not  less  than  3  feet  wide  and  not  more  than  7  feet  long.* 

Beds  are  as  a  rule  made  horizontal,  except  in  the  facing,  but  in 
the  Remsheid  Dam,  completed  in  1891,  the  joints  were  made  to  vary 

somewhat  according  to  the  line  of  pressure 
as  shown  in  Fig.  98.  Greater  resistance 
against  shearing  is  thus  obtained. 

Cement  mortar  should  be  made  in  such 
proportions  as  to  be  practically  impervious, 
particularly  near  the  up-stream  face.  Port- 
land or  Rosendale  cement  mortar  2  to  I, 
or  Portland  3  to  I,  is  usually  employed, 
but  the  last  is  not  entirely  impervious. 
It  is  desirable  to  use  the  stronger  mortar 
where  the  heavier  stresses  exist  and  also 
near  the  faces. 

The  size  of  stone  to  be  used  in  rubble 
masonry  depends  chiefly  on  the  matter  of 
convenience.  In  some  of  the  modern 
dams  stones  measuring  6  to  8  cubic  yards  have  been  used.  Large 
spaces  are  left  between  these  which  are  filled  with  cement  or  with 
smaller  stones  and  mortar. 

In  constructing  the  masonry  the  principal  points  to  be  emphasized 
are  clean  surfaces,  irregular  surfaces,  joints  absolutely  filled  with  com- 
pact mortar,  no  grouting,  great  care  to  give  good  bedding,  and  con- 
stant supervision.  Mortar  and  cement  should  be  thoroughly  rammed 
into  all  spaces,  using  for  this  purpose  suitable  forms  of  rammers. 

*  Wegmann.     The  Water-supply  of  New  York,  p.  207. 


FIG.  98.— THE  REMSHEID  DAM. 


396  MASONRY  DAMS. 

Concrete  to  be  practically  impervious  should  not  usually  have  a 
greater  proportion  of  sand  and  stone  than  that  given  by  the  mixture  of 
1:3:5.  Larger  proportions  of  stone  have  been  used,  however,  with 
good  results,  such  as  I  :  3j  ':  7^.*  The  greater  the  proportion  of  stone 
the  better,  as  long  as  all  voids  are  rilled,  but  with  high  ratios  of  stone 
greater  care  is  required  in  the  manipulation.  Close  supervision  in  the 
mixing  and  laying  is  very  necessary  to  secure  a  good  concrete. 

The  water  of  streams  is  cared  for  during  construction  by  methods 
similar  to  those  described  in  the  preceding  chapter  (page  370). 

441.  Imperviousness. — Imperviousness    is    very  difficult  to  secure, 
and  in  fact  most  masonry  dams  leak  slightly.    That  it  can  be  practically 
obtained  is,    however,    shown  by  the  results  reported   in  the  case  of 
several  of  the  modern  dams.     The  result  in  this  respect  depends  chiefly 
upon  the  care  taken  in  executing  the  work.      Special  precautions  may, 
however,  be  used  to  good  advantage,  such  as  the   use  of  a  more  im- 
pervious mortar  near  the  up-stream  face  of  the  dam,  or  the  plastering 
of  the  upper  face  with  neat  or  i-to-i  cement  mortar.    In  the  Remsheid 
Dam  a  continuous  joint  of  asphalt  was  used  just  back  of  the  face-stones 
and  on  the  foundation  surface  for  a  short  distance  above  the  dam. 

Whether  cracks  will  necessarily  form  in  dams  is  a  disputed  point. 
In  some  they  have  occurred  and  in  some  apparently  not.  In  long  nar- 
row walls  cracks  are  very  sure  to  form,  due  to  temperature  changes, 
but  in  the  massive  walls  of  dams  the  changes  in  the  interior  are  very 
slight,  and  it  is  undoubtedly  true  that  in  some  of  the  modern  dams 
at  least,  no  cracking  of  the  interior  has  occurred.  In  the  Vyrnwy  Dam 
the  effect  of  temperature  changes  has  been  measured  at  a  height  of  80 
feet.  A  maximum  movement  of  0.366  mm.  due  to  variations  in 
temperature  from  day  to  night  has  been  noted. t  In  the  Remsheid 
Dam,  curved  at  410  feet  radius  and  82  feet  high,  a  movement  of  the 
crest  of  iT1g-  inches,  due  to  filling  of  the  reservoir,  and  of  -J  inch,  due 
to  temperature  changes,  has  been  observed.  The  curved  form  was 
here  considered  to  have  prevented  cracking.^ 

442.  Earth  Backing  for  Masonry  Dams. — In   the   construction    of 
dams   of  moderate   height,   earth  backing  is   often   carried  up  to   the 
water-level  with  a  slope  of  2  or  3  to  I,  as  in  an  earthen  dam.     Such  a 
backing,  if  more  porous  than  the  dam,  will  not  reduce  the  pressure 

*  See  description  of  Indian  River  Dam  in  Eng.  News,  1899,  XLI.  p.  310  ;  also  a 
paper  by  G.  W.  Rafter  on  the  Theory  of  Concrete  in  Trans.  Am.  Soc.  C.  E.,  1899, 
XLII.  p.  104. 

\  Proc.  Inst.  C.  E.,  cxv.  p.  117. 

\  Eng.  News,  1896,  xxxv.  p.  76. 


CONSTRUCTION 


397 


against  the  wall,  but  will  rather  increase  it  and  is  ordinarily  of  doubtful 
advantage.  If,  however,  a  dam  is  located  on  a  porous  or  bad  founda- 
tion or  on  one  of  earth,  a  good,  compact  backing  will  much  reduce  the 
percolation  under  the  dam,  and  therefore  the  tendency  of  any  upward 
pressure,  and  will  add  considerably  to  the  safety  of  the  structure.  It  is 
especially  applicable  to  spillways  in  earthen  embankments.  The  earth 
backing  in  that  case  acts  also  as  a  protection  for  the  back  of  the 
masonry  against  injury  from  ice  and  driftwood.  (See  Figs.  97  and 
104.) 


•- El.  244, 03 


Section  through  Gate-house. 
Paving 


Section  through  Waste-weir. 
Ormied  Slope 


Plan  of  Gate-house  and  Wing  Wall. 
FIG.  99. — DAM  No.  5,  BOSTON  WATER-WORKS. 

(From  Engineering  News,  vol.  xxxm.) 

443.  Draw-off  Arrangements, — The  arrangements  for  drawing  water 
from  the  reservoir  are  similar  in  general  to  those  described  in  the  last 
chapter.  The  outlet-pipes  are  built  in  the  masonry  at  or  near  the 
lowest  point  of  the  dam,  and  terminate  in  a  gate-chamber  constructed 
just  above  and  in  connection  with  the  dam.  The  gate-chamber  has 


39^ 


MASONRY  DAMS. 


the  same  functions  as  explained  in  the  case  of  earthern  embankments. 
No  danger  is  here  to  be  apprehended  from  constructing  the  pipes  in  the 
body  of  the  dam. 

An  outlet  arrangement  of  common  form  is  shown  in  Fig.  99,  which 
illustrates  details  of  Dam  No.  5  of  the  Boston  Metropolitan  Water- 
works. The  figure  shows  the  weir,  gate-house,  and  wing  walls  at  the 
junction  of  the  earth  embankment  and  masonry  dam.  The  gate-cham- 


-Com**. 


SlidingJoint 
Longitudinal  Section  H-H 


-  Overflow  Chamber. 
Sluice  Gcrfes 
Rec&vincf  Chamber: 


FIG.  99a. —  THE  BOONTON  DAM. 

(From  Engineering  Record,  vol.  XLIX.) 


ber  is  very  similar  to  those  used  in  several  of  the  dams  of  the  New 
York  Water-works.  (For  section  of  the  earth  embankment,  see  Fig.  74.) 

Another  very  good  example  of  gate-chamber  and  draw-off  arrange- 
ments is  shown  in  Fig.  99a.  Notice  the  large  steel  outlet-pipes  and 
reducers  permitting  the  use  of  36-in.  valves  on  48~in.  pipes. 

Simpler  arrangements  than  the  above  may  often  be  adopted  to 
advantage.  Thus  if  screening  is  not  required,  a  single  chamber  answers 


DRA  W-OFF  ARRANGEMENTS. 


399 


every  purpose.  Even  this  is  dispensed  with  in  some  cases,  as  for 
example,  in  the  construction  of  the  large  dam  at  Butte,  Mont.,  and 
more  recently  in  the  dam  at  Plymouth,  England.  In  these  cases  the 
outlet-pipes  pass  through  the  dam  and  terminate  in  short  vertical  pipes 
just  above  the  upper  face.  Cover-valves  are  fitted  over  the  ends  of 
these  pipes  and  are  operated  by  chains  from  windlasses  above.  Details 
of  the  valves  used  at  Plymouth  are  illustrated  in  Fig.  100.  As  shown 
in  the  sectional  elevation,  the  valve  is  made  in  three  sections  which  are 
successively  raised  when  the  valve  is  opened.  This  form  of  construc- 


Ha  If  Plan  of  Second, 
and  Third  Rings.  < 


Sectional  Plan 
of  Bellmoutti. 


FIG.  100.  —  COVER-VALVES,  PLYMOUTH  RESERVOIR,  ENGLAND. 

(From  Engineering  Newst  vol.   XLII.) 


tion  is  best  suited  to  the  case  where  the  valves  need  not  be  often 
operated.  In  the  winter  the  ice  would  have  to  be  kept  cut  away  from 
around  the  chains  or  pipes. 

Where  a  dam  is  built  across  a  narrow  valley  a  scouring-sluice  or 
large  waste-pipe  placed  at  the  lowest  point  will  enable  much  of  the  silt 
deposit  to  be  removed  by  flushing.  These  deposits  may  be  prevented 
to  some  extent  by  building  small  barricades  or  dams  at  the  entrance 
of  the  various  streams  into  the  reservoir,  thus  forming  small  settling- 
basins  which  may  be  more  readily  cleaned  than  the  large  reservoir. 
Flood-channels  are  also  sometimes  constructed  in  the  case  of  small 
streams  which  are  used  to  lead  flood-waters  that  are  not  needed  around 
the  end  of  the  dam  and  thus  prevent  to  some  extent  the  accumulation 
of  sediment. 


400  MASONRY  DAMS. 

444.  Masonry  Waste-weirs, — Masonry  dams  are  not  usually  designed 
to  allow  water  to  pass  over  their  entire  length,  but  a  certain  portion 
only  is  made  to  act  as  a  waste-weir.  As  was  the  case  with  earthen 
dams,  the  waste-weir  is  often  located  at  the  extreme  end  of  the  dam, 
the  overflow  passing  down  a  prepared  channel  in  the  hillside.  Whether 
it  is  so  placed,  or  located  more  nearly  in  the  axis  of  the  valley,  depends 
chiefly  upon  the  topography  and  nature  of  the  foundations. 

The  form  of  a  masonry  weir  depends  much  upon  local  conditions, 
chief  of  which  are  height  of  dam,  character  of  foundation,  amount  of 
ice  and  driftwood  to  be  expected,  and  quantity  of  water  to  be  provided 
for.  A  weir  is  essentially  a  dam  with  its  top  and  lower  face  so  con- 
structed as  to  permit  the  water  to  pass  over  it  without  damage.  Besides 
the  design  of  the  profile,  the  protection  of  the  stream-bed  below  the 
dam  is  a  very  important  feature,  as  many  dams  have  !been  undermined 
by  failure  at  this  point  even  where  the  bed  has  been  solid  rock. 

With  respect  to  the  form  of  construction,  masonry  weirs  may  be 
divided  into  three  classes:  (i)  weirs  with  a  nearly  vertical  front  face, 
allowing  a  free  fall  to  the  water ;  (2)  weirs  with  a  curved  lower  face ; 
(3)  weirs  with  a  stepped  lower  face. 

445 •  (T)  Weirs  Allowing  Free  Fall. — These  are  ordinarily  used  for 
low  falls  of  10  to  20  feet,  depending  on  the  character  of  the  bottom. 
The  front  face  is  made  at  a  batter  of  I  to  2  inches  per  foot,  and  the  rear 
face  whatever  is  necessary  to  secure  stability.  The  top  width  is  made 
sufficient  to  resist  the  impact  of  ice,  logs,  etc.,  5  to  8  feet  usually  being 
sufficient.  The  cap  stones  should  incline  downwards  up-stream,  to 
relieve  them  from  blows  on  the  back  edge.  They  must  be  large  and 
well  laid,  and,  where  subject  to  severe  shocks,  well  doweled  and 
clamped  together.  It  may  also  be  necessary  to  anchor  the  masonry  to 
•the  bed-rock.  With  earth  foundations,  an  earth  backing,  finished  with 
gravel  or  paving,  is  often  carried  up  flush  with  the  back  edge.  The 
advantage  of  this  has  been  noted  in  Art.  442. 

If  the  stream-bed  is  not  solid  rock,  it  must  be  well  protected  by  an 
apron  of  timber  or  stone,  the  former  being  quite  temporary  unless  con- 
stantly wet.  A  timber  apron  is  usually  made  as  a  continuation  of  the 
foundation  platform  with  additional  layers  of  thick  planking.  A  stone 
apron  varies  in  construction  according  to  the  requirements  from  a  mere 
paving,  to  a  heavy  apron  of  broken  stone,  concrete,  and  one  or  more 
layers  of  heavy  paving  set  in  cement. 

With  falls  greater  than  10  or  20  feet,  aprons  alone  are  not  sufficient 
security  against  scour,  and  even  with  rock  bottom  the  wear  becomes  too 
great,  especially  if  large  quantities  of  ice  and  logs  pass  over  the  weir. 


MASONRY   WASTE    WEIRS. 


401 


Free  falls  for  greater  heights  may  still  be  used  by  protecting  the  bed 
by  means  of  a  water-cushion,  formed  by  a  subsidiary  weir  built  a  short 
distance  below  the  main  weir.  This  reduces  the  height  of  fall  and  also 
forms  a  pond  into  which  the  water  falls  and  which  absorbs  its  energy. 
The  depth  of  such  a  water-cushion  depends  on  the  mass  of  water  and 
character  of  the  bed.  It  is  frequently  made  one-fifth  or  one-fourth  the 
height  of  the  main  weir. 

An  example  of  a  weir  of  considerable  height  having  a  free  fall  is  the 
Macoupin  Intake  Dam  of  the  East  Jersey  Water  Company,  illustrated  in 
Fig.  10 1,  Clemens  Herschel,  Mem.  Am.  Soc.  C.  E.,  engineer.  The  coping- 
stones  are  well  doweled  together  and  bolted  to  the  body  of  the  dam.  The 
stream-bed  is  solid  rock.  (See  also  Fig.  97,  page  393.) 


FIG.   1 01.  —  MACOUPIN  INTAKE  DAM 


446.  (2)  Weirs  with  a  Curved  Lower  Face. — The  object  of  this 
form  is  to  guide  the  water  smoothly  over  the  dam,  and  at  the  bottom 
to  deliver  it  tangentially  with  respect  to  the  stream-bed.  In  this  way 
the  water  arrives  at  the  bottom  with  nearly  the  same  velocity  as  with 
a  free  fall  but  with  changed  direction,  a  great  advantage  where  logs 
and  ice  pass  over  the  dam.  The  scouring  effect  is,  however,  very 
great,  and  in  high  weirs  a  water-cushion  is  here  also  necessary  where 
large  volumes  are  dealt  with.  If  the  depth  of  water  is  slight,  the 
velocity  may  be  reduced  by  leaving  the  surface  of  the  weir  very  rough, 
as  in  the  Vyrnwy  Dam.  For  high  weirs  the  section  is  designed  as 
for  a  high  dam  (making  due  allowance  for  the  extra  pressure  due  to 
the  superelevation  of  the  water-surface,  and  for  shocks,  etc.),  and  then 
rounded  off.  The  rear  face  is  made  nearly  vertical,  as  in  high  dams. 


402  MASONRY  DAMS. 

The  convex  top  curve  to  be  given  to  a  dam  should  be  full  enough 
to  prevent  the  water  leaving  the  surface.  This  will  be  given  by  the 
parabolic  curve  which  the  water  would  take  in  a  free  fall  with  the 
initial  horizontal  velocity  corresponding  to  the  depth  on  the  weir. 
According  to  the  formula  for  weirs,  the  average  velocity  of  the  water 
is  v  =  c.\^2gH.  (See  page  229.)  In  time  /  the  abscissa  of  the 

<r 
parabola  is  x  =  vt,  and  the  ordinate  is y  =  \gt*,  whence y  —  — ^  is 

the  equation  of  the  parabola.  In  a  long  weir  with  ends  not  freely 
exposed  to  the  entrance  of  air  the  normal  pressure  is  not  maintained 
under  a  sheet  of  water,  and  it  will  be  forced  by  the  exterior  pressure  to 
follow  a  sharper  curve  than  the  parabola  above.  Such  action  is  very 
observable  in  many  weirs. 

-J.60 


—-  66 -* 

FIG.   102. — COLORADO  RIVER  DAM  AT  AUSTIN,  TEXAS. 

A  noteworthy  example  of  a  large  dam  made  to  act  as  a  weir  is  the  dam 
across  the  Colorado  River  at  Austin,  Texas,  built  for  water-power  purposes 
(Fig.  102).  This  structure  is  1275  feet  long  and  is  built  of  rubble  with 
granite  facing.  It  was  designed  to  pass  flood-waters  to  a  depth  of  about  15 
feet  on  the  crest,  but  on  April  7,  1900,  during  a  flood  in  which  the  depth  of 
water  flowing  was  about  1 1  feet,  a  large  section  of  the  dam  failed,  a  portion 
sliding  down-stream  and  remaining  upright,  while  a  portion  was  broken  up  and 
washed  away.  The  cause  of  the  failure  is  not  definitely  known,  but  some 
weakening  of  the  foundation  is  evident,  due  either  to  erosion  by  percolation 
or  by  the  water  falling  below  the  dam.*  This  dam  is  an  exception  in  respect 
to  its  height  and  the  great  volume  of  water  to  be  provided  for,  and  the  protec- 
tion of  the  stream-bed  from  the  action  of  the  great  mass  of  water  is  in  such  a 
case  a  matter  of  very  great  importance. 

Fig.  103  illustrates  another  dam  built  for  power  purposes  and  designed 
for  a  large  flow.  The  facing  of  this  dam  is  also  of  granite,  the  curve  for  the 

*  See  Eng.  News,  April  12,  1900,  et  $eq.\  Eng.  Record,  April  14,  1900,  et  seq. 


WASTE    WEIRS. 


403 


upper  portion  being  a  parabola  corresponding  to  the  curve  of  the  flowing 
water  when  4  feet  deep.  The  stones  are  thoroughly  doweled  together.  The 
lower  portion  of  the  dam  is  cycloidal,  and  the  upward  slope  of  the  toe  is  intro- 
duced so  as  to  form  somewhat  of  a  water-cushion.* 

447«  (3)  Weirs  with  a  Stepped  Profile. — In  this  form  the  lower  face 
is  stepped  instead  of  curved,  with  the  object  of  breaking  the  fall  into 
several  small  steps  and  absorbing  the  energy  of  the  water  before  it 
reaches  the  bottom.  This  very  much  simplifies  the  problem  of  scour, 


FIG.  103. — THE  NEW  HOLYOKE  DAM  ACROSS  THE  CONNECTICUT  RIVER. 

and  at  the  same  time  gives  a  form  cheaper  to  construct  than  the  curved 
outline.  It  is  well  suited  to  carry  moderate  quantities  of  water.  With 
the  stepped  profile  the  wear  comes  more  on  the  dam,  while  with  the 
curved  form  it  is  more  on  the  stream-bed.  The  masonry  of  the  steps 
requires  to  be  of  the  heaviest  and  most  substantial  character.  Single 
stones  should  be  used  extending  well  under  the  masonry  above. 

An  example  of  a  spillway  of  considerable  height  is  shown  in  Fig.  104,  a 
section  of  the  Dunning' s  Dam,  E.  Sherman  Gould,  Mem.  Am.  Soc.  C.   E.p 


FIG.  104. — THE  DUNNING'S  DAM. 

engineer.  The  dam  is  noteworthy  as  being  partly  founded  on  rock  and  partly 
on  earth,  conditions  very  difficult  to  deal  with.  The  weir  is  founded  on  clay 
and  fine  sand.  The  apron  consists  of,  first,  a  filling  of  large  stones,  then  one 
foot  of  concrete,  then  a  heavy  paving  in  cement  mortar.  Below  is  a  timber 
crib  filled  with  stones,  and  farther  down,  the  channel  is  riprapped.  The  dam 

*  Eng.  News,  1897,  xxxvu.  p.  292. 


404 


MASONRY  DAMS. 


is  backed  with  earth,  which  is  considered  by  the  designer  as  being  a  valuable 
safeguard  for  a  masonry  dam.* 

Fig.  105  is  a  section  through  the  highest  portion  of  the  spillway  of  the 


FIG.  105.  —  SPILLWAY,  NEW  CROTON  DAM. 

New  Croton   Dam.     This  design  may  be  considered  as  well  representing 
modern  practice  in  this  direction. 


FIG.  106. — DAM  AT  TROY,  N.  Y.  FIG.  107.  —  INDIAN  RIVER  DAM,  N.  Y- 


*  Trans.  Am.  Soc.  C.  E.,  1804,  xxxii.  p.  737. 


EXAMPLES   OF  MASONRY  DAMS.  405 

448.  Other  Examples  of  Dams.  —  Fig.  106  illustrates  a  concrete  spillway 
for  a  dam  of  moderate  height.  It  constitutes  a  part  of  the  water-works  of 
Troy,  N.  Y.  This  spillway  adjoins  an  earthern  embankment,  the  abutments 
being  partially  shown  in  the  figure.* 

Fig.  107  illustrates  a  small  modern  dam  across  Indian  River,  N.  Y., 
in  the  upper  Hudson  valley,  built  for  water-power  and  navigation  purposes. 
The  dam  is  of  rubble  masonry  with  spaces  filled  with  concrete,  f 

On  page  406  are  illustrated  the  sections  of  several  of  the  largest  dams  of 
the  world,  all  sections  being  drawn  to  the  same  scale.  Of  these  dams  the  New 
Croton  will,  when  completed,  be  the  largest.  This  dam  consists  of  a  masonry 
portion,  of  the  section  shown,  for  a  length  of  about  700  feet,  a  curved  masonry 
spillway  at  one  end  1000  feet  long  (Fig.  105),  and  at  the  other  end  an  earthen 
embankment  with  masonry  core-wall  (Fig.  75,  page  351).  The  masonry  dam 
has  a  maximum  height  above  foundation  of  about  290  feet,  measuring  to  the 
deepest  pocket.  In  section  it  is  practically  the  same  as  adopted  for  the 
Quaker  Bridge  Dam.  The  height  of  spillway  varies  from  10  to  150  feet. 
Rubble  masonry  is  used  for  hearting,  and  ashlar  for  facing.  The  steps  on  the 
waste-weir  are  to  be  made  of  block  masonry,  and  of  sufficient  depth  to  bond 
under  the  step  above.  The  estimated  cost  of  this  dam  is  nearly  $5,000,000. 
It  was  begun  in  1892,  and  will  be  completed  about  1903. 

The  Vyrnwy  dam,  which  is  a  part  of  the  Liverpool  Water-works,  is  note- 
worthy on  account  of  the  great  care  taken  to  obtain  strong,  impervious 
masonry,  and  in  the  provision  made  for  drainage.  It  is  built  of  large  rubble 
masonry,  a  large  proportion  of  the  blocks  ranging  from  2  to  8  tons  in  weight. 
All  stones  were  washed  and  scrubbed  with  jets  of  water  under  140  feet 
pressure.  The  mortar  was  made  of  Portland  cement  i  to  2  and  i  to  2-J,  the 
sand  being  composed  of  pulverized  rock  mixed  with  natural  sand.  Large 
stones  were  bedded  upon  a  2-inch  layer  of  mortar  which  was  first  beaten  to 
expel  the  air.  The  stones  were  also  beaten  into  place  by  blows  from  hand- 
mauls.  The  spaces  between  the  stones  were  filled  with  small  rubble  or  concrete 
rammed  into  place.  The  crushing  strength  of  the  concrete,  one  year  old, 
was  about  187  tons  per  square  foot.  The  specific  gravity  of  the  masonry  was 
found  to  be  about  2.5.  The  maximum  pressure  at  the  upper  face  is  8.7  tons 
and  at  the  lower  face  6.36  tons  per  square  foot.  To  prevent  the  existence 
of  hydrostatic  pressure  in  the  dam  a  system  of  drains  was  constructed  in  the 
foundation.  These  drains  are  9  to  12  inches  square  and  are  kept  25  feet  from 
the  front  face.  They  connect  with  a  concrete  tunnel  4  feet  by  2  feet  6  inches 
wide  running  longitudinally  through  the  dam  and  46^  feet  above  the  base. 
This  opens  out  to  the  surface  by  a  cross-tunnel.  Length  of  dam  =  1350  feet. 
Maximum  height  —  136  feet.  It  is  designed  to  act  as  a  waste- weir. | 

The  San  Mateo  Dam  in  California  is  noteworthy  as  having  been  built 
entirely  of  concrete  blocks,  each  of  about  9  tons  weight. 

The  Furens  Dam,  France,  is  famous  as  being  the  first  one  constructed  on 
scientific  principles,  and  until  recently  the  highest  dam  in  existence.  It  was 
completed  in  1866. 

The  Periar  Dam,  Madras,  is  another  notable  concrete  dam.  The  maxi- 
mum pressure  intensity  is  stated  to  be  8  tons  per  square  foot. 

*  Eng.  News,  1904,  LH.  p.  300. 
t  Eng.  News,  1899,  XLI.  p.  310. 
t  Proc.  Inst.  C.  E.,  cxxvi.  p.  24. 


406 


MASONRY  DAMS. 


New   Groton 


5an    Mateo 


r 


Scale  of  Feet 


-//7Z5- 
Vyrnwtj 


FIG.  108.  —  PROFILES  or  SOME  HIGH  MASONRY  DAMS. 


DAMS   OF    THE  BUTTRESS    TYPE. 


407 


448a.  Dams  of  the  Buttress  Type.  —  Considering  again  the  two  por- 
tions of  a  dam,  the  impervious  part  and  the  supporting  part,  the 
question  arises  if  a  portion  of  the  material  of  a  masonry  dam,  which 
serves  merely  as  supporting  material,  might  not  be  omitted.  This  can 
be  done  in  various  ways. 

The  up-stream  face  may  be  made  in  the  form  of  masonry  arches  and 
these  supported  on  piers  or  buttresses ;  a  steel  facing  may  be  employed 
in  place  of  the  masonry  arches;  or  a  covering  of  reinforced  concrete 
may  be  used.  Since  the  development  of  reinforced  concrete  the  last 
named  method  has  been  employed  in  several  cases  with  resulting 
economy. 

In  the  design  of  a  buttress  type  of  dam  the  buttresses  are  propor- 
tioned for  the  entire  pressure.  For  high  dams  they  must  therefore  be 
made  considerably  broader  than  the  base  of  a  dam  of  solid  section. 
The  position  of  the  line  of  pressure  can  readily  be  varied  by  varying 
the  slope  of  the  face.  A  special  advantage  of  this  type  of  dam  in  .cer- 
tain cases  is  that  it  permits  the  buttress  foundations  to  be  constructed 
as  separate  piers. 

Fig.  io8a  illustrates  the  concrete  dam  at  Ogden,  Utah,  built  for  the  Pioneer 
Power  Plant.  The  piers  are  concrete  walls  16  feet  thick  with  32  feet  in  the 
clear,  and  the  concrete  arches  vary  from  6  to  8  feet  in  thickness.  The  arches 
are  protected  and  rendered  more  impervious  by  a  covering  of  steel  plates, 
although  this  covering  is  not  essential.  In  this  dam,  100  feet  high  and  400 


P)orn 
FIG.  io8a.  —  CONCRETE  DAM,  OGDEN,  UTAH. 

feet  long,  the  quantity  of  masonry  is  given  as  26,000  cubic  yards  as  compared 
to  37,200  cubic  yards  estimated  for  a  dam  of  ordinary  section.  The  actual 
cost,  including  steel  covering,  was  12  to  15  per  cent  less  than  that  of  an 
ordinary  dam.  The  maximum  pressure  is  10.7  tons.  Instead  of  concrete 


408 


MASONRY  DAMS. 


arches,  a  steel  face  formed  of  steel  plates  was  also  considered,  but  was  found 
to  be  more  expensive  than  the  adopted  design.* 

The  other  dam  of  this  sort  is  on  the  Belubula  River,  New  South  Wales. 
It  was  there   adopted  on  account  of  the  ridgy  nature  of  the  bottom.     The 

height  is  60  feet,  length  431  feet,  with  six 
buttresses  28  feet  apart  center  to  center, 
40  feet  long  and  5  to  1 2  feet  thick.  Brick 
arches  were  used,  4  feet  thick  at  bottom  and 
igi  i  foot  7  inches  at  top,  built  at  an  angle  of 
60  degrees  with  the  horizontal.! 

Fig.  io8b  illustrates  the  usual  form  of 
reinforced  concrete  dam  where  the  water  may 
be  allowed  a  free  fall  or  where  no  water 
passes  over  the  dam.  It  consists  of  separ- 
ate concrete  buttresses  spaced  about  8  feet 
apart,  supporting  an  inclined  floor  of  rein- 
forced concrete.  As  regards  strength  the 
method  of  design  is  evident.  \  In  such  structures  large  factors  of  safety 
should  be  employed  and  at  all  points  subject  to  impact  the  dimensions  will 
usually  need  to  be  much  greater  than  called  for  by  the  static  load  in  order  to 
provide  sufficient  weight  and  mass. 

Fig.  io8c  illustrates  the  dam  at  Schuylerville,  N.  Y.     This  has  a  down- 
stream floor  or  apron  and  is  designed  to  act  as  a  spillway.    To  avoid  any 


_L 


FIG.  io8b. — DAM  AT  ELLS- 
WORTH, ME. 


Crest 


134.00 


FIG.  io8c. —  DAM  AT  SCHUYLERVILLE,  N.  Y. 

internal  pressure  due  to  seepage  through  the  Up-stream  face,  drain  openings 
are  provided  in  the  down-stream  face.§ 

Where  constructed  upon  earth  foundation,  a  continuous  floor  of  rein- 
forced concrete  from  buttress  to  buttress  may  be  used  to  spread  the  load 
and  to  prevent  scour.  The  entire  structure  thus  becomes  a  monolith  and 
is  exceedingly  strong  and  rigid.  Thus  built  it  may  be  safely  constructed 

*  Trans.  Am.  Soc.  C.  E.  1897,  xxxvm.  p.  291. 
t  Eng.  News,  1898,  LX.  p.  148. 
\  Ibid.  1904,  LII.  p.  255. 
§  Ibid.  1905,  LIII.  p.  448. 


LITER  A  TURE.  409 

on  pile  foundations,  care  being  taken  to  cut  off  seepage  at  the  up-stream 
toe  by  means  of  sheet  piling  well  connected  to  the  concrete. 

449.  Cost.  —  The  cost  of  constructing  masonry  dams  will  vary 
greatly  with  the  local  conditions.  If  these  are  reasonably  favorable  as 
to  transportation  and  ease  of  securing  stone,  the  range  of  prices  for  the 
principal  items  will  be  about  as  follows  :  Earth  excavation  25  to  50 
cents  per  cubic  yard  ;  rock  excavation  $1.00  to  $2.00  ;  rubble  masonry, 
natural  cement,  $4.00  to  $6.00 ;  concrete  masonry,  natural  cement, 
$4.00  to  $6.00;  for  masonry  laid  in  Portland  cement  add  about  $1.00 
per  cubic  yard;  reinforced  concrete  $8.00  to  $12.00,  including  steel ; 
rock-faced  ashlar  masonry  $10.00  to  $15.00;  dimension-stone  masonry 
for  gate-houses,  etc.,  $15.00  to  $30.00;  paving  $2.00  to  $3.00;  riprap 
$1.50  to  $2.00. 

LITERATURE. 

1.  Krantz.     A  Study  on  Reservoir  Walls.     New  York,  1883. 

2.  Wegmann.     Design  and  Construction  of  Dams.     New  York,  1907. 

3.  Coventry.     The  Design  and  Stability  of  Masonry   Dams.     Proc.   Inst. 

C.  E.,   1885-86,  LXXXV.  p.   281. 

4.  Grugnola.      The  Gileppe  Dam,   near  Verviers,  Belgium.      Eng.  News, 

1886,  xvi.  p.  418. 

5.  The  New  Water-works  at  Bridgeport,  Conn.  Eng.  News,  1887,  xvn.p.23o. 

6.  Fteley.     High  Masonry  Dams.     Eng.  News,  1888,  xix.  pp.  74,  92. 

7.  Rock-fill  Reservoir  Dams.     Eng.  News,  1888,  xx.  p.  69.     . 

8.  Strains  in  Curved  Dams.     Eng.  News,  1888,  xx.  pp.  429,  513. 

9.  Schuyler.     The  Construction  of  the  Sweetwater  Dam.     Trans.  Am.  Soc. 

C.  E.,  1888,  xix.  p.  201. 

10.  Francis.     High  Walls  or  Dams  to  Resist  the  Pressure  of  Water.     Trans. 

Am.  Soc.  C.  E.,  1888,  xix.  p.  147. 

11.  Report  of  the   Board   of  Experts  on  the  Quaker   Bridge   Dam.     Eng. 

News,  1888,  xx.  p.  344. 

12.  The  New  Bear  Valley  Dam.     Eng.  News,  1889,  xxn.  p.  484. 

13.  Strains  in  Curved  Dams.     Eng.  News,  1890,  xxiv.  p.  148. 

14.  Jobson.      Beetaloo  Water-works,   South   Australia.       Proc.  Inst.  C.  E., 

1892-93,  cxiii.  p.   151. 

15.  The  New  Concrete  Masonry  Dam  of  the  Butte  City  Water  Company, 

E?ig.  News,  1892,  xxviii.  pp.  554,  584. 

1 6.  Clerke.     The  Tansa  Works  for  the    Water-supply  of   Bombay.     Proc. 

Inst.  C.  E.,  cxv.  p.  12. 

17.  The  New  Water-power  and  Water-supply  at  Austin,  Tex.      Eng.  News, 

1892,  xxvin.  p.  152. 

1 8.  Groves.     The  Austin  Dam.     Eng.  News,  1893,  xxix.  p.  86. 

19.  The  Austin  Dam  Controversy.     Eng.  Record,  1893,  xxvu.  p.  155.     Also 

various  articles  in  Eng.  News,    1892,  xxviii.      The  discussion  is 
largely  on  the  question  of  the  flow  of  water  over  wide-topped  weirs. 

20.  Coventry.     Note  on  the  Stresses  in  Masonry  Dams.     Proc.  Inst.  C.  E., 

1893-94,  cxvi.  p.  334. 

21.  McCulloh.     The  Construction  of  a  Water-tight  Masonry  Dam.     Trans. 

Am.  Soc.  C.  E.,  1893,  xxvni.  p.  185. 


410  MASONRY  DAMS. 

22.  Kreuter.     On  the  Design  of  Masonry  Dams.     Proc.  Inst.  C.  E.,  1893-94, 

cxv.  p.  63. 

23.  The  Bhatgur  Dam,  India.     Eng.  News,  1893,  xxix.  p.  391. 

24.  Carroll.     The  Basin  Creek  Dam  for  the  Water-works  of  Butte,  Mont. 

Eng.  News,  1893,  xxx.  p.  139. 

25.  Pelletreau.     Profile  sans  Extensions  des  Grands  Barrages  en  Maconnerie. 

Annales  des  Ponts  et  Chaussees,  1894,  i.  p.  619. 

26.  La  Grange   Dam  for  Turlock-Modesto  Irrigation  Districts,  Cal.      Eng. 

News,  1894,  xxx.  p.  266  ;  Eng.  Record,  1894,  xxix.  p.  216. 

27.  Ulrich.     Sewall  Falls  Dam  across  the  Merrimack  River,  near  Concord, 

N.  H.     Eng.  News,  1894,  xxi.  p.  326. 

28.  Van  Buren.     Notes  on  High  Masonry  Dams.     Trans.  Am.  Soc.  C.  E., 

1895,  xxxiv.  p.  493. 

29.  The  Titicus  Dam.     Eng.  Record,  1895,  xxxn.  p.  68. 

30.  Deacon.     The  Vyrnwy  Works  for  the  Water-supply  of  Liverpool.     Proc. 

Inst.  C.  E.,  1895-96,  cxxvi.  p.  24. 

31.  Intze.       Die     Erweiterung    des    Wasserwerkes    der    Stadt    Remscheid. 

Zeitschr.  d.   Ver.  deutsch.  Ing.  1895,  xxxix.  p.  639.      Describes 
a  large  curved  dam.     Abstract,  Eng.  News,  1896,  xxxv.  p.  76. 

32.  Schuyler.     Water-storage   and   Construction  of   Dams.     U.    S.   Geolog. 

Survey,  1896-97,  Part  IV.  p.  617.     Describes  and  illustrates  numer- 
ous dams. 

33.  Hardesty.     The  Water-supply  System  of  Salt  Lake  City,  Utah.     Eng. 

News,  1896,  xxxvi.  p.  258.     Describes  a  large  concrete  dam. 

34.  Thompson.     The  New  Holyoke  Water-power  Dam.     Eng.  News,  1897, 

xxxvii.  p.  292. 

35.  Schuyler.     The   Construction  of  the  Hemet  Dam.     Jour.   Assoc.  Eng. 

Soc.,  1897,  xix.  p.  81. 

36.  The  Power  Plant  of  the  Hudson  River  Power  Company,  at  Mechanicsville, 

N.  Y.     Eng.  News,  1898,  XL.  p.  130. 

37.  The  New  Croton  Dam.     Eng.  Record,  1898,  xxxvni.  p.  27. 

38.  Rafter,  Greenalch,  and  Horton.     The  Indian  River  Dam.     Eng.  News, 

1899,  XLI.  p.  310. 

39.  Concrete  Dam  for   the  Vierfontein   Water  Syndicate,  S.  Africa.     Eng. 

Record,  1899,  xxxix.  p.  112. 

40.  The  New  Masonry  Dam  at  Holyoke,  Mass.     Eng.  Record,  1899,  XL. 

p.  1 66. 

41.  Gowan.     The  Foundations  of  the  New  Croton  Dam.      Trans.  Am.  Soc. 

C.  E.,  1900,  XLIII.  p.  469. 

42.  Lippincott.      Exploration   for   Bed-rock   at   Gila   River   Dam-sites   with 

Diamond  Drills.     Eng.  News,  1900,  XLIII.  p.  34. 

43.  The  Wachusett   Dam.     Eng.    Record,  1900,  XLII.  p.  218.     Illustrated 

description  of  dam  and  details  of  gate-chamber. 

44.  Gregory.     Stability  of  Small  Dams.     Eng.  Record,  1901,  XLIV.  p.  269. 

45.  Rufneux.     Resistance  des  Barrages  en  Maconnerie.     Au.  des  Ponts  et 

Chaussees,  1901,  I.  Trim. 

46.  Cadart.    Barrages  a  Parements  Rectilignes.    Au.  des  Ponts  et  Chaussees. 

1902,  in.  Trim. 

47.  Dillman.     A  Proposed  New  Type  of  Masonry  Dam.     Trans.  Am.  Soc. 

C.  E.,  1902,  XLIX.  p.  94. 

48.  The  Assonan  Dam  and  the  Assiout  Weir.     Engr.,  Dec.  12,  1902. 


LITERATURE.  411 

49.  The  Spier    Falls  Dam  of   the  Hudson    River  Water   Power   Company. 

Eng.  News,  1903,  XLIX.  p.  553. 

50.  The    New   Water- works   of   Jersey   City.      The    Boonton    Dam.      Eng. 

Record,  1903,  XLVIII.  p.  153. 

51.  Rubble  Concrete   Dam   for   the   Atlanta   Water  &  Electric   Power  Co. 

Eng.  News,  1904,  LII.  p.  15. 

52.  Harrison  and  Woodard.     Lake  Cheesman  Dam  and  Reservoir.     Trans. 

Am.  Soc.  C.  E.,  1904,  LIII,  p.  89.     In  the  discussion,  a  bold  arch 
type  of  dam  at  Ithaca,  N.  Y.,  is  described. 

53.  Moncrieff.     The    Barossa   Arched    Concrete   Dam    in    South   Australia. 

Eng.  News,  1904,  LI.  p.  321. 

54.  A  Hollow  Reinforced  Concrete  Dam  at  Schuylerville,  N.  Y.     Eng.  News, 

1905,  LIII.  p.  448. 

55.  Reinforced  Concrete  Dam  at  Fenelon  Falls,  Ont.     Eng.  News,  1905,  LIII. 

P-  135- 

56.  The  Roosevelt  Masonry  Dam  on  Salt  River,  Arizona.     Eng.  News,  1905, 

LIII.  p.  34. 

57.  Wiley.     Masonry   Dam  for  the  Granite    Springs   Reservoir,   Cheyenne, 

Wy.      Eng.    Record,   1905,  LI.   p.    698 ;    Eng.  News,    1905,    LIII. 
p.  671. 

58.  The  Stability  of  Masonry  Dams.     Review  of  Theory  of  Atcherly  &  Pear- 

son relative  to  the  Assouan  Dam.     Engng.,  Mch.  31,  1905  ;  Engr., 
Mch.  31,  1905. 

59.  Unwin.    Notes  on  the  Theory  of  Unsymmetrical  Masonry  Dams.    Engng., 

Apr.  21,  May  12,  1905. 

60.  Unwin.     The    Distribution    of    Shearing  Stresses    in    Masonry    Dams. 

Engng.,  June  30,  1905. 

6 1.  Reinforced  Concrete    Dam,  Dellwood    Park,  111.     Eng.   Record,  1907, 

LV.  p.  164. 

62.  Wegmann.     The  Design  of  the  New  Croton  Dam.     Proc.  Am.  Soc.  C.  E., 

June,  1907. 

FAILURES    OF    MASONRY    DAMS. 

1.  Schuyler.     The  Failure  of  the  Lynx  Creek  Masonry  Dam,  near  Prescott, 

Ariz.     Eng.  News,  1898,  xxxix.  p.  362. 

2.  Failure   of  the   Angels    Masonry   Dam,  Calaveras   County,  Cal.     Eng. 

News,  1895,  xxxiii.  p.  307. 

3.  Failure  of  the  Bouzey  Dam.     Proc.  Inst.  C.  E.,  1896,  cxxv.  p.  461. 

4.  The  Failure  of  the  Austin  Dam.     Full  account,  including  many  special 

reports  in  several  of  the  numbers  of  Eng.  Record  and  Eng.  News 
subsequent  to  the  failure,  April  7,  1900. 

5.  Haraway.     Recent  Failures  of  Masonry  Dams  in  the  South.     Eng.  News, 

1902,  XLVII.  p.  107. 

6.  Gillette.     Coefficient  of  Friction  in  Dam  Designs  and  the  Failure  of  the 

Dam  at  Austin,  Tex.     Eng.  News,  1901,  XLV.  p.  392. 


CHAPTER   XVIII. 
TIMBER   DAMS;  LOOSE-ROCK    DAMS;  STEEL    DAMS. 

TIMBER   DAMS. 

450.  Use  of  Timber  Dams, — Where  a  weir  is  constantly  submerged, 
a  timber  structure  is  of  a  permanent  nature,  and  will  need  repairs  only 
on  account  of  the  wear  of  the  apron.  A  timber  dam  may  also  be 
advisable  in  certain  circumstances  even  when  its  life  will  be  short,  as, 
for  example,  where  a  temporary  supply  may  be  furnished  pending  the 
construction  of  more  permanent  works,  or  where  the  expense  of 
permanent  and  costly  structures  is  for  the  present  prohibitory.  Such 
dams  are,  however,  used  mostly  for  diversion  purposes  or  for  water 
power,  and  seldom  for  the  storage  of  large  volumes  of  water. 

Timber  dams  may  be  constructed  on  any  kind  of  a  foundation,  but 
are  usually  built  on  rock  or  on  a  gravelly  bed.  They  consist  of  cribs 
or  frames  built  of  logs  or  squared  timber,  filled  with  stone  and  clay, 
and  planked  over  to  render  them  water-tight.  They  may  be  built  as 
separate  cribs  in  sections,  each  section  consisting  of  perhaps  3  to  4 
cribs,  or  as  one  continuous  framework.  The  former  method  is 
especially  useful  in  dealing  with  large  flows  and  irregular  foundations, 
the  stream  being  gradually  closed  as  the  sections  are  constructed. 
The  cribs  may  also  be  filled  and  sunk  separately  so  as  to  form  piers  on 
which  a  continuous  structure  may  be  built. 

The  foundation  of  a  crib  dam,  if  soft,  is  prepared  by  dumping  stone 
over  the  area  to  be  built  upon.  In  the  framed  dam  the  foundation 
must  be  more  carefully  prepared.  Where  it  is  soft  the  dam  is  supported 
on  piling,  and  sheet-piling  is  used  to  prevent  underflow.  If  the  dam 
is  built  on  a  rock  bottom,  it  must  be  bolted  thereto.  The  framework  is 
usually  built  with  a  sloping  upper  face  and  a  series  of  stepped  aprons 
below,  or  a  single  free  fall  to  a  water-cushion.  Rock  and  gravel,  or 
puddle  is  used  for  filling. 

412 


TIMBER  DAMS. 


413 


451.  Examples  of  Timber  Dams. — Sewall  Falls  Dam  (Fig.  109).  —  This 
dam  across  the  Merrimack  is  a  crib  dam  497  feet  long,  constructed  on  a  hard- 
pan  foundation.  It  was  built  in  sections  by  means  of  coffer-dams,  sluiceways 


FIG.  109.  —  SEWALL  FALLS  DAM. 

(From  Engineering  News,  vol.  xxxi.) 

being  left  in  the  completed  portion  to  carry  the  water  during  the  construc- 
tion of  the  last  sections.  The  longitudinal  pieces  are  12  X  1 2-inch  hemlock 
and  Southern  pine,  and  the  ties  10  X  lo-inch  hemlock,  all  fastened  together 
by  drift-bolts.  The  spaces  were  hand-packed  with  stone.  The  aprons  are 
made  of  steel  on  account  of  heavy  ice.  The  figure  shows  the  construction 
clearly.  The  life  of  the  structure  is  estimated  by  the  engineers  at  fifty  to 
sixty  years.  The  cost  was  about  60  per  cent  that  of  a  stone  dam,  the  contract 
price  being  $120,000.* 

452.  Bear  River  Weir.  —  Fig.  no  is  a  section  of  a  timber  weir  across  the 
Bear  River,  Utah,  built  to  divert  water  for  irrigating  purposes.  The  founda- 
tion is  solid  rock  into  which  the  timbers  are  bolted.  All  timbers  are  i  o  X  12- 


^^^yfj-^^^SK^S^^ 


Cross     Section . 

FIG.  no.  —  BEAR  RIVER  DAM. 

(From  Engineering  News,  vol.  xxxv.) 


Side  Elevation. 


inch.  The  interior  is  filled  with  stone,  and  a  heavy  layer  of  earth  is  placed  at 
the  back  to  prevent  percolation.  In  the  middle  of  the  stream  the  apron  con- 
sists of  10  X  i2-inch  timbers,  instead  of  the  second  layer  of  3-inch  plank  as 
shown.  A  portion  of  the  dam  founded  on  gravel  and  boulders  was  badly 
underscoured  in  1891.  This  part  was  afterwards  protected  by  two  rows  of 

*  Eng.  News,  1894,  xxxi.  p.  326. 


414  TIMBER   DAMS;   LOOSE-ROCK  DAMS;   STEEL   DAMS. 

sheet-piling  4  feet  apart,  driven  at  the  back  side,  the  space  between  being 
filled  with  concrete.  The  whole  was  then  covered  with  earth  and  boulders.* 
453.  Butte,  Mont.,  Crib  Dam.  —  In  Fig.  in  is  illustrated  a  crib  built 
at  Butte,  Mont.,  and  notable  for  its  great  height.  The  dotted  portion  shows 
the  section  of  the  spillway.  The  height  from  low  water  to  crest  is  56  feet. 
It  is  founded  on  a  bed  of  stiff  clay  and  boulders  12  to  35  feet  below  the  sur- 
face. A  concrete  wall  4  feet  thick  extends  from  the  foundation  to  a  point 


FIG.  in. —  TIMBER  DAM  AT  BUTTE,  MONT. 

(From  Engineering  Record,  vol.  xxxvn.) 

about  6  feet  above  the  original  surface,  as  shown  in  the  figure.  The  remainder 
of  the  excavation  is  filled  with  clay  puddle,  well  rammed.  The  dam  is  made 
of  10  X  i2-inch  pine  timbers  and  filled  with  granite  packed  in  layers  in  the 
crib-work.  Soon  after  completion  this  structure  partially  failed  under  a 
heavy  flood.  The  pressure  of  the  water  caused  the  highest  portion  to  settle 
or  cant  over  (the  top  moving  some  7  or  8  feet  down-stream),  and  the  entire 
structure  to  settle  vertically.  At  one  place  twenty-seven  1 2-inch  timbers  were 
compressed  to  a  thickness  of  24  feet  10  inches.  The  failure  was  due  to  lack 
of  resistance  to  shearing  forces,  and  to  the  compression  of  the  timbers  at  the 
joints.  The  filling  was  not  sufficiently  compact  to  render  the  structure  rigid, 
and  no  diagonal  bracing  was  used.t 

LOOSE-ROCK  DAMS. 

454.  Loose-rock  Dams.  —  Dams  composed  largely  of  loose  rock  have 
been  used  to  a  considerable  extent  in  the  West,  and  in  some  respects 
present  considerable  advantages  as  to  stability.  Another  advantage  is 
that  they  can  be  constructed  in  running  water,  but  the  finished  dam  is 
not  suited  to  act  as  a  waste-weir. 

The  body  of  the  dam  is  made  of  loose  rock  placed  with  more  or 
less  care,  and  rendered  comparatively  impervious  by  a  sheathing  of 
plank,  or  by  a  facing  of  earth  or  fine  material  on  the  upper  face,  or,  as 
in  one  case,  by  a  core  of  steel.  As  regards  stability  the  principle  of 

*  Eng.  News,  1896,  xxxv.  p.  84.    t  Eng.  Record,  1898,  xxxvn.  p.  301,  xxxvm.  p.  203. 


LOOSE-ROCK  DAMS.  415 

construction  is  of  the  best.  Since  considerable  percolation  is  likely  to 
take  place,  such  a  dam  cannot  be  founded  on  a  material  liable  to  scour  ; 
and  if  the  dam  is  high,  the  foundation  should  be  solid  rock.  The  lower 
slope  is  usually  I  to  i ,  while  the  upper  slope  may  be  made  \  or  \  to  i  ; 
but  to  secure  these  steep  slopes  it  is  necessary  to  lay  the  stone  for  a 
considerable  thickness  as  a  dry  wall.  Above  this  wall  the  facing  of 
timber  or  earth  is  placed.  The  former  material  is  objectionable  on 
account  of  its  perishable  nature. 

Rock-fill  dams  have  been  constructed  where  a  stratum  of  loose 
material  of  considerable  thickness  has  overlaid  the  solid  rock.  In  such 
a  case,  as  the  dam  is  built  up  the  loose  material  gradually  scours  out 
and  the  loose  rock  settles  into  place.  On  such  a  foundation  both 
slopes  must  be  made  quite  flat  and  no  reliance  can  be  placed  on  retain- 
ing-walls  of  any  sort. 

A  disadvantage  of  rock-fill  dams  is  in  the  relatively  large  loss  of 
water  which  occurs,  an  important  consideration  in  the  case  of  storage- 
reservoirs.  The  cost  of  such  dams  has  in  some  cases  been  very  low, 
in  one  instance  as  low  as  45  cents  per  cubic  yard. 

455.  Examples.  —  Fig.    112    shows   the  section   of  the   dam   at   Pecos, 
N.  Mex.     The  facing  here  is  of  earth. 

A  rock-fill  dam  with  timber  facing  is  shown  in  Fig.  113,  the  Escondido 
Dam  in  California.  The  upper  portion  of  the  dam  is  laid  as  a  dry  wall  with 
a  thickness  of  from  5  to  15  feet.  The  height  is  76  feet.  The  outlet  is  a 
24-inch  cast-iron  pipe  laid  in  concrete  and  having  a  valve  at  the  upper  end.* 

An  interesting  example  of  a  rock-fill  dam  is  illustrated  in  Fig.  114,  which 
represents  the  lower  Otay  Dam  in  southern  California,  already  referred  to  on 
page  351  as  having  a  steel  core.  A  masonry  dam  had  been  considered  for 
this  place,  but  owing  to  the  great  depth  to  bed-rock  the  plans  were  changed. 
The  construction  is  clearly  shown  in  the  figures.  The  lower  figure  shows  to  an 
enlarged  scale  the  method  of  joining  the  steel  and  masonry  core  to  the  founda- 
tion at  the  ends  of  the  dam.  The  rock  forming  the  dam  was  placed  by 
dumping  from  a  cableway.  The  leakage  is  very  slight.  Another  very 
notable  example  of  the  rock-fill  type  is  the  dam  at  Laguna,  Ariz.,  across  the 
Colorado  River,  f 

STEEL   DAMS. 

456.  Steel  Cores.  —  The  use  of  steel  cores  and  facings  for  concrete, 
loose  rock  and  earthen  dams  has  been  noted  in  Arts.  455,  448a,  and 
391.     In  such  cases  the  steel  is  employed  to  furnish  or  insure  the 
desired  impervious  face ;  the  supporting  element  is  furnished  by  other 
material. 

*  Eng.  News,  1898,  xxxvm.  p.  63. 
I  Ibid.,  1908,  LIX,  p.  213. 


416  TIMBER  DAMS ;  LOOSE-ROCK  DAMS;   STEEL  DAMS. 


'  \  "-Rough  Laid  Wall    >> 


FIG.  112. —  PECOS  DAM. 

(From  Engineering  News,  vol. xxxvi.) 


FIG.  113. —  ESCONDIDO  DAM. 


El.  130.0 


(a) 


FIG.  114. —  LOWER  OTAY  DAM. 

(From  Engineering  News,  vol.  xxxix.) 


LITER  A  TURE.  4 1 7 

457.  Dams  built  wholly  of  Steel.  —  A  dam  entirely  of  steel  has  been 
built  in  Arizona,  at  Ash  Fork.  The  face  consists  of  curved  plates  f 
inch  thick  imbedded  at  the  bottom  in  concrete.  The  greatest  height  is 
46  feet.  The  plates  are  riveted  to  a  system  of  inclined  struts  resting 
on  a  rock  foundation.  Expansion  is  taken  up  by  a  slight  bending 
in  the  curved  plates.  Such  a  form  as  this  possesses  a  great  advan- 
tage in  the  definiteness  with  which  the  stresses  can  be  calculated 
and  provided  for,  and  the  fact  that  the 
stability  of  the  structure  is  independ- 
ent of  the  imperviousness  of  the  face. 
Its  chief  disadvantages  lie  in  the  cost 
for  maintenance  and,  probably,  in  its  lack 
of  durability,  a  point  not  yet  well  deter- 
mined. Fig.  1 1 5  shows  the  form  of 
bracing  at  the  highest  portion.*  Another 
notable  steel  dam  is  that  across  the 
Missouri  River,  near  Helena,  Mont. 

A  comparative  estimate  for  a  6o-foot 
dam,  made  in  connection  with  the  Ogden 

Dam  described  above,  gave    for   a    steel  FIG.  115.  — STEEL  DAM,  ASH  FORK, 

ARIZONA. 
dam    of    the  form  shown  in  Fig.    1 1 5  a 

weight  of  7000  pounds  per  lineal  foot  ;  for  a  cantilever  design  for  a  steel 
dam  8050  pounds  per  lineal  foot ;  and  for  an  ordinary  masonry  dam 
48  cubic  yards  per  lineal  foot.f 

LITERATURE. 

TIMBER    DAMS. 

1.  Parker.     Black  Eagle  Falls  Dam,  Great  Falls,  Mont.     Trans.  Am.  Soc. 

C.  E.,  1892,  xxvii.  p.  56. 

2.  Clarke.     Crib  Dam.     Trans.  Am.  Soc.  C.  E.,  1895,  xxxiv.  p.  507. 

3.  Hardesty.     The  Bear  River  Irrigation  System,  Utah.     Eng.  News,  1896, 

xxxv.  p.  83. 

4.  Woermann.     A  Low  Crib  Dam  across  Rock  River.     Jour.  Assoc.  Eng. 

Soc.,  1896,  xvn.  p.  54. 

5.  Bishop.     The    Lachine    Rapids    Power    Plant,    Montreal,    P.    Q.     Eng. 

News,  1897,  xxxvn.  p.  98. 

6.  The  Butte,  Montana,  Power  Plant.    Eng.  Record,  1898,  xxxvn.  p.  301. 

7.  Parker.     Partial  Failure  of  Timber  Dam  near  Butte,  Mont.     Eng.  Record, 

1898,  xxxvin.  p.  203. 

8.  The    Reconstructed    Canyon    Ferry    Dam,    near    Helena,    Mont.     Eng. 

News,  1900,  XLIII.  p.  266. 

9.  Tower.     Timber  Dam  at    the   Outlet  of   Chesuncook    Lake,  Penobscot 

River.     Eng.  News,  1904,  LII.  p.  191. 

*  Eng.  N'eivs,  1898,  xxxix.  p.  299. 

t  Trans.  Am.  Soc.  C.  E.,  1897,  xxxvm.  p.  305. 


41 8  TIMBER  DAMS;   LOOSE-ROCK  DAMSj   STEEL   DAMS. 


LOOSE-ROCK   DAMS. 

1.  Wells.     The  Castlewood  Dam.     Eng.  Record,  1898,  xxxix.  p.  69.     Eng. 

Record,  July,  1902,  p.  34. 

2.  Parker.    East  Canyon  Creek  Dam,  Utah.     Rock-fill  dam  with  steel  core. 

Eng.  Record,  1899,  XL.  p.  313. 

3.  Reconstruction  of  the  Castlewood  Dam.     Eng.  Record,  1902,  XLVI.  p.  34. 

4.  Hardesty.     A  Rock-fill  Dam  with  Steel  Core  across  East  Canyon  Creek, 

)  Utah.    Eng.  News,  1902,  XLVII.  p.  14. 

5.  Parsons.     A    Small    Rock-fill    Dam.     Trans.    Am.    Soc.    C.  E.,   1903,  L. 

P-  35 1- 

6.  The    Five   Dams   and  Wood-Stave  Conduit    of   the    Southern  California 

.  Mountain  Water  Co.      Two  rock-fill  dams  and  two  with  steel  cores. 
Eng.  News,  1904,  LI.  p.  335  ;  Eng.  Record,  1903,  XLVIII.  p.  590. 

7.  Harrison    and     Woodward.       Lake     Cheesman     Dam    and    Reservoir. 

Failure  of  a  rock-fill  dam  described.     Trans.  Am.  Soc.  C.  E.,  1904. 
LIII.  p.  89. 

8.  The  Construction  of  the  Laguna  Dam,  Colorado  River,  Ariz.     Eng.  News, 

1908,  LIX.  p.  213. 

STEEL     DAMS. 

1.  Thompson.     Reservoir  Dams,  with  Iron  Sheeting.     The  Engineer,  1896, 

LXXXI.  p.  459- 

2.  Steel   Weir,  Ash   Fork,  Ariz.     Eng.   Record,  1898,  xxxvn.  p.  404;  Eng. 

News,  1898,  xxxix.  p.  299. 

3.  The  Redridge  Dam.     Eng.  News,  1901,  XLVI.  p.  101. 

4.  Bainbridge.     Structural  Steel  Dams.     Jour.  West.   Soc.  Engrs.,   1905,  x. 

p.  615  ;  Eng.  News,  1905,  LIV.  p.  323. 

5.  The  Hauser  Lake  Steel  Dam  in  the  Missouri  River  near  Helena,  Mont. 

Eng.  News,  1907,  LVIII.  p.  507. 

6.  Sizer.     The  Break   in  the   Hauser  Lake  Dam,  Montana.      Eng.  JVewst 

1908,  LIX.  p.  491. 


B.  WORKS  FOR  THE   PURIFICATION  OF  WATER 

CHAPTER    XIX. 
OBJECTS   AND    METHODS   OF   PURIFICATION. 

458.  Purification  of  Water  for  Manufacturing  Purposes. — In  the  puri- 
fication of  water-supplies,  reference  is  generally  made  to  the  treatment 
of  water  designed  for  domestic  use,  but  the  subject  may  also  -be  con- 
sidered   as    applied   to    water   intended   for   manut'acturing   purposes. 
Generally  speaking,  in  technical  industries  and  for  manufacturing  pur- 
poses a  soft   water   is   desired,  also   one   that    is   free   from   organic 
impurities.     In   such  industries  as  brewing,  distilling,  and   sugar  and 
starch  manufacturing,  the  question  of  germ  content  is  more  important, 
as  water  containing  some  kinds  of  micro-organisms  is  apt  to  produce 
abnormal    fermentations    that    injure    the    product.       Iron-containing 
waters  are  particularly  detrimental  in  the  manufacture   of  paper  and 
pulp,  also  in  dye-works.     These  technical  industries,  however,  demand 
a  special  examination  in  selecting  a  proper  source  of  water-supplies, 
and  generally  do  not  pertain  to  the  ordinary  work  of  a  water-works 
engineer. 

For  general  manufacturing  purposes  it  is  desired  that  a  water  should 
not  readily  form  boiler-scale.  The  precipitation  of  certain  inorganic 
salts,  particularly  those  of  calcium  and  magnesium,  interferes  much  with 
the  economic  action  of  boilers  as  steam-generators.  The  accumulation 
of  this  incrustation  to  a  thickness  of  one-sixteenth  inch  involves  a  loss 
variously  stated  at  from  12  to  20  per  cent  of  the  energy  of  the  coal 
used.  The  methods  of  purifying  water  so  as  to  remove  the  mineral 
ingredients  capable  of  forming  boiler-scale  deserve,  therefore,  careful 
consideration. 

459.  Purification  of  Water  for  Domestic   Purposes.  —  In  ordinary 
household  use  the  quality  of  water  is  of  considerable  import.     Not  only 
is  a  water  that  is  rich  in  alkaline  earths  not  well  adapted  for  cooking 
and  similar  purposes,  but  on  account  of  its  action  upon  soap  it  is  very 

419 


420  OBJECTS  AND    ME7^HODS   OF  PURIFICATION. 

undesirable  for  general  household  use.  In  a  hard  water,  soap  is 
decomposed  and  the  fatty  acids  unite  with  calcium  and  magnesium 
salts,  forming  insoluble  compounds  under  such  circumstances.  To 
secure  the  cleansing  action,  it  becomes  necessary  to  use  a  much  larger 
amount  of  soap.  The  removal  of  the  hardening  impurities  of  a  water 
constitutes,  therefore,  an  important  feature  of  water  purification.  Its 
economic  value  is  well  illustrated  by  the  case  of  Glasgow  already 
mentioned  in  Art.  150. 

In  purifying  a  drinking-water  there  may  be  two  objects  in  view. 
That  which  is  the  most  important  is  the  treatment  of  the  water  in  a 
way  so  as  to  remove  any  danger  from  pathogenic  organisms ;  in  addi- 
tion, however,  waters  may  be  purified  so  as  to  improve  their  physical 
appearance.  This  latter  object,  while  it  ought  to  be  subordinated  to 
the  former,  often  is  not,  and  in  the  eyes  of  the  consumer  an  unsavory 
water  will  often  cause  more  complaint  than  a  pure  sparkling  water  that 
may  be  polluted  with  disease  organisms.  Not  all  waters  destined  to 
be  used  as  drinking-water  supplies  need  artificial  purification.  Ground- 
or  spring-waters  rarely  need  to  be  artificially  treated,  as  they  have 
already  been  purified  by  the  operation  of  natural  forces  (Chapter  IX). 
They  sometimes  need  treatment  for  the  removal  of  iron,  but  generally 
speaking,  so  far  as  deleterious  bacteria  are  concerned,  they  are  com- 
paratively safe  if  they  are  normal  ground-waters. 

The  waters  that  need  artificial  purification  most  are  those  that 
remain  in  contact  with  the  surface  of  the  soil.  Not  infrequently  it  is 
possible  to  secure  a  surface  supply  that  is  perfectly  wholesome,  but  the 
opportunity  for  pollution  is  too  often  present,  and  the  only  regions  in 
which  unpolluted  waters  are  likely  to  be  found  are  those  that  are 
sparsely  settled.  With  the  increasing  density  of  population,  surface 
waters  are  in  general  becoming  more  and  more  dangerous,  until  in 
many  sections  it  has  become  impossible  to  furnish  a  supply  that  is  safe 
without  the  use  of  some  method  of  artificial  purification.  This  condi- 
tion is  seen  in  the  steady  increase  of  the  typhoid  death-rates  in  many 
of  the  cities  that  are  supplied  with  waters  from  surface  sources. 

460.  Outline  of  Methods  of  Purification  Employed. — Numerous  pro- 
cesses of  purification  have  been  devised  and  tested  experimentally  to  a 
greater  or  less  extent,  but  in  actual  practice  only  a  few  have  been 
found  feasible.  While  many  of  the  methods  have  been  the  outgrowth 
of  empirical  testing,  others  have  been  devised  as  the  result  of  a  thorough 
study  of  the  principles  that  have  been  found  to  underlie  these  processes 
as  they  occur  under  natural  conditions  or  where  artificially  controlled. 

The    various   processes   of  purification    may   be    divided   into    two 


METHODS   OF  PURIFICATION  EMPLOYED.  421 

general  groups:  (i)  those  for  the  removal  of  suspended  impurities,  and 
(2)  those  for  the  removal  of  dissolved  impurities.  Of  the  first  class 
there  are  two  general  processes,  sedimentation  and  filtration,  both  of 
which  may  be  called  natural  processes.  By  sedimentation,  water  may 
be  more  or  less  freed  of  its  suspended  matters,  including  the  bacteria, 
the  efficiency  of  the  treatment  depending  much  upon  the  element  of 
time.  The  process  is  carried  out  artificially  in  large  storage-reservoirs 
or  in  small  special  settling-basins.  It  is  often  aided  by  the  introduction 
of  some  chemical  that  will  produce  a  precipitate  which  will  readily 
settle  and  carry  down  with  it  the  more  finely  divided  matter  in  suspen- 
sion. Variations  in  the  method  of  operation  of  settling-basins  and  in 
the  introduction  of  the  chemical  give  rise  to  various  modifications  of  the 
general  process. 

Filtration  is  accomplished  in  different  ways.  The  most  common  is 
by  means  of  the  artificial  sand-filter  bed,  either  as  contained  in  masonry 
basins  of  large  size,  or  confined  in  small  tanks  as  in  the  mechanical 
filters.  Special  forms  of  filtering  media  have  also  been  devised,  such 
as  the  Fischer  tile  filter,  also  filters  made  of  asbestos,  and  the  various 
forms  of  small  filters  for  domestic  purposes.  The  chief  object  is  in  all 
cases  the  removal  of  the  suspended  matters,  and  in  most  public  supplies 
particular  attention  is  paid  to  the  removal  of  bacteria.  In  many 
instances  chemical  changes  occur  in  filters,  but  they  are  not  often  of 
any  great  importance. 

The  p^cesses  for  the  removal  of  dissolved  impurities  include  the 
softening  process,  in  which  lime  and  magnesia  are  removed  by  chemical 
precipitation,  and  the  process  for  the  removal  of  iron  in  a  similar 
manner.  Such  methods  usually  involve  subsequent  sedimentation  or 
filtration  for  the  removal  of  the  precipitate.  In  the  iron  treatment  the 
filtration  itself  sometimes  plays  an  important  part  also  in  the  chemical 
changes  involved.  Aeration  consists  in  bringing  air  into  intimate  con- 
tact with  all  parts  of  the  water.  This  acts  both  to  supply  deficient 
oxygen  and  also  to  drive  out  objectionable  dissolved  gases.  It  often 
constitutes  an  important  part  of  other  processes. 

Besides  the  above-mentioned  processes  there  should  be  mentioned 
the  method  of  purification  by  distillation,  in  which  practically  all 
impurities  are  removed,  and  the  various  methods  of  sterilization,  in 
which  the  bacteria  are  simply  killed. 

From  the  preceding  statements  it  will  be  seen  that  each  problem 
in  water  purification  demands  individual  treatment;  and  that  the  best 
method  to  adopt  in  any  case  will  depend  upon  the  character  of  the 
water  and  the  use  to  which  it  will  be  put,  both  of  which  elements  are 


422  OBJECTS  AND   METHODS   OF  PURIFICATION. 

subject  to  many  variations.  No  one  process  is  universally  applicable  ; 
furthermore,  of  two  processes  for  removing  the  same  kind  of  impurity, 
the  most  efficient  may  not  in  all  cases  be  the  best.  The  highest 
efficiency  is  not  always  necessary,  and  in  such  cases  economy  may 
properly  be  secured  by  the  adoption  of  a  system  of  less  efficiency  but 
of  lower  cost. 

In  1902  there  were  reported  the  following  number  of  cities  of  more 
than  3000  population  using  the  various  methods  of  purification :  — * 

Slow  sand  filters    21 

Rapid  or  mechanical  filters 141 

Sedimentation  basins 53 

Filter  galleries 14 

Filter  cribs    1 1 

Softening  plants   2 

Aerating  plants    5 

LITERATURE. 

WORKS    TREATING    OF    VARIOUS    PURIFICATION    PROCESSES. 

1.  Delhotel.     Trait£  de  1'Epuration  des  Eaux  Naturelles  et  Industrielles. 

Paris,  1893. 

2.  Rideal.     Water  and  its  Purification.     London,  1897. 

3.  Hill.     The  Purification  of  Water-supplies.     New  York,  1898. 

4.  Fuller.     Water  Purification  at  Louisville.     New  York,  1898.     Report  of 

extensive  experiments  on  sedimentation,  sand  and  mechanical  filtra- 
tion, and  the  use  of  coagulants. 

5.  Fuller.     Report    on  Water    Filtration  at   Cincinnati.     City  Doc.,    1899. 

Experiments  on  'sedimentation,  sand  and  mechanical  filtration,  and 
the  use  of  lime  as  a  coagulant  with  subsequent  filtration  through 
polarite. 

6.  Hazen.     Report  to  the  Filtration  Commission,  Pittsburgh.     City  Doc., 

1899.  Experiments   on    sand    and    mechanical    filtration    and   the 
Fischer  tile  system. 

7.  Hazen.     The  Filtration   of   Public  Water-supplies.       New  York,   1900. 

Treats  of  filtration,  coagulation,  and  removal  of  iron.  Contains 
bibliography. 

8.  Report  on  Water-purification  Experiments  at  Washington,  D.  C.     Senate 

Doc.  No.  259;  Fifty-sixth  Cong.,  First  Sess.     Abstract,  Eng.  News, 

1900,  XLIII.  p.  315.     Sand  and  mechanical  filtration.     Also  Senate 
Report  No.  2830,  56th  Cong.,  2d  Sess. 

9.  Knowles.     Description  of  Experimental  Filter  Plant  at  Pittsburgh,  and 

Results  of  Experiments.     Jour.  New  Eng.  W.  W.  Assn.,  1900,  xv. 
p.  148. 
10.    Water    Purification    in    the    U.  S.       Statistics,  Eng.  News,  1902,  XLVII. 

P-  3^0- ' 

*  Eng.  News,  1902,  XLVII.  p.  310. 


LITER  A  TURE.  423 

11.  Weston.     Report   on    Water  Purification   Investigation.     New  Orleans, 

1903.     Eng.  Record,  1903,  XLVH.  p.  606. 

12.  Weston.     The    Water-supply    of    New    Orleans    and    its    Improvement. 

Jour.  New  Eng.  W.  W.  Assn.,  1903,  xvn.  p.  157. 

13.  Purification   of    Water    for    Domestic  Use.     Papers    on    American    and 

European  Practice.     International  Eng.   Cong.,  1904;  Trans.  Am. 
Soc.  C.  E.,  1905,  LIV.  D. 

14.  Maignen.     Different    Methods   of    Purifying   Water.     Proc.  Eng.  Club. 

Phil.,  Jan.,  1907. 


CHAPTER   XX. 
SEDIMENTATION   AND    COAGULATION. 

461.  In  the  case  of    many  surface  supplies  the  water  contains  at 
various  times  large  quantities  of  suspended  matter,  either  with  or  with- 
out more  serious  polluting  substances ;  and  a  considerable  part  of  the 
work  of  purification  consists  in  the  removal  of  this  suspended  matter  so 
as  to  improve  the  physical  appearance  of  the  water. 

462.  The  Character  of  the  Suspended  Matter.  —  In  streams  such  as 
would  be  considered  suitable  as  sources  of  supply  the  sediment  is  prin- 
cipally of  an  inorganic  nature,  consisting  of  particles  of  sand  and  clay 
of   various   sizes.     There   is  also   usually   a  small  amount  of   organic 
matter,  and,  in  addition,  varying  numbers  of  bacteria,  which,  although 
too  minute  to  render  the  water  turbid,  yet  are  of  the  greatest  impor- 
tance on  account  of  their  possible  relation  to  disease.     During  seasons 
of  high  turbidity,  the  bacterial  content  is  usually  very  high,  owing  to 
the    large    numbers    derived   from    the    surface    drainage    of   the   soil. 
Varying  numbers  may  also  be  derived  from  sewage  pollution,  but  the 
bacteria  from  this  source  are  usually  more  numerous  during  the  seasons 
of  low  water  when  the  turbidity  is  at  a  minimum.     The  amount  and 
character  of  the  sediment  varies  greatly  from  time  to  time,  as  pointed 
out  in  Chapter  IX  ;  it  depends  largely  upon  the  stage  of  water  in  the 
different  tributaries,  and  upon  the  geological  character  of  the  various 
parts  of   the  drainage-area.     Thus   Fuller  found   that  the  amount   of 
sediment  in  the  Ohio  River  water  at  Louisville  varied  from   I  to  5000 
parts  per  million,  ranging  ordinarily  from   100  to  1000;  and  that  the 
bacteria  varied  from  a  few  hundred  per  c.c.  to  as  high  as  50,000.* 

The  size  of  the  suspended  particles  varies  greatly.  In  some  waters 
the  finer  particles  of  clay  are  less  than  o.ooooi  inch  in  diameter,  which 
is  smaller  even  than  bacteria.  This  great  variation  in  amount  and 
kind  of  sediment  constitutes  one  of  the  most  troublesome  factors  in 
connection  with  purification  works  for  river  supplies.  For  example,  at 
New  Orleans  the  water  is  much  more  difficult  to  treat  than  at  St.  Louis, 
although  containing  a  lower  percentage  of  sediment. 

*  Water  Purification  at  Louisville,  1898,  p.  15. 

424 


LIMITATIONS   OF  ARTIFICIAL   SEDIMENTATION. 


425 


The  average  amount  of    sediment  carried    by  various   river  waters 
used  as  public  water-supplies  is  reported  as  follows  :  * 


Citv 

River. 

Suspendec 

Matter. 

Parts  per 
Million. 

Tons  per  Mil- 
lion Gallons. 

Lawrence                                       .... 

Merrimac    .    . 

IO 

o  04.2 

Albany                  

Hudson   .    .    . 

1C 

O  062 

Pittsburgh         

Allegheny    .    . 

CQ 

O   208 

Potomac 

80 

O    3?'? 

Ohio 

2  7O 

O    Q^7 

Louisville                                      

Ohio             .    . 

"1<O 

I    480 

New  Orleans           ~     

Mississippi  .    . 

25 

o^o 

2    7O 

St    Louis                    

Mississippi 

IOOO 

4  16 

463.  Limitations  of  Artificial  Sedimentation.  —  In  Chapter  IX  the 
marked  effect  of  natural  sedimentation  upon  the  character  of  water  in 
rivers  and  lakes  was  pointed  out,  — such  effect,  for  example,  as  may  be 
observed  in  any  natural  lake  or  pond  fed  by  sediment-carrying  streams. 
Where  the  body  of  quiescent  water  is  sufficiently  large,  and  the  period 
of  repose  sufficiently  long,  this  action  of  sedimentation  becomes  practi- 
cally perfect,  and  a  clear  and  greatly  improved  water  is  the  result. 
Artificially,  such  high  efficiency  is  often  obtained  where  the  water  is 
collected  in  large  impounding-reservoirs  holding  several  months'  supply. 
Where,  however,  the  supply  is  taken  directly  from  a  large  sediment- 
bearing  stream,  very  large  reservoirs  are  usually  impracticable  on 
account  of  the  great  cost ;  and  the  period  of  time  during  which  sedi- 
mentation can  be  operative  must  therefore  be  limited  to  a  few  days  or 
even  to  a  few  hours.  Such  a  limited  amount  of  sedimentation  is, 
however,  of  much  value. 

In  general  the  longer  the  time  of  storage  within  practicable  limits 
the  better  the  result ;  but  the  value  of  large  reservoirs  lies  not  only  in 
the  length  of  time  allowed  for  settlement,  but  also  in  the  opportunity 
thus  afforded  for  shutting  off  the  river  supply  at  times  of  great  turbidity. 
This  is  an  especially  valuable  feature  in  the  case  of  streams  of  moderate 
size  where  the  high-water  stage  lasts  but  a  few  days.  Its  value  in 
water  purification  has  been  long  recognized  in  England.  In  cities 
where  an  elevated  location  can  be  found  for  a  storage-reservoir  so  that 
it  may  also  act  as  a  distributing-reservoir,  the  advantages  above  noted, 
together  with  those  pertaining  to  the  matter  of  distribution,  would 


Weston.     Report  on  Filtration  at  New  Orleans,  1903,  p.  171. 


426  SEDIMENTATION  AND    COAGULATION.  \ 

properly  lead  to  the  adoption  of  relatively  large  sizes.  (See  Chapter 
XXVII  for  further  discussion  of  distributing-reservoirs.) 

Where  a  water  contains  little  that  is  objectionable  besides  the 
inorganic  sediment,  a  degree  of  purification  can  often  be  obtained  by 
mere  sedimentation  which  will  render  the  water  fairly  acceptable.  In 
many  instances,  however,  a  satisfactory  water  cannot  be  obtained  with- 
out subsequent  filtration ;  but  in  this  case  the  process  of  sedimentation 
constitutes  a  very  valuable  and  almost  indispensable  prerequisite  to  the 
final  treatment.  For  a  sewage-polluted  water,  sedimentation  alone  is 
an  inadequate  treatment,  as  the  bacteria  are  not  eliminated  in  sufficient 
numbers  to  insure  safety. 

464.  Methods  of  Sedimentation.  —  There  are  two  methods  to  be  con- 
sidered :  (i)  Plain  sedimentation;  (2)  Sedimentation  with  the  addition 


of  a  coagulant. 


PLAIN    SEDIMENTATION. 


465.  Action  of  Subsidence.  —  The  particles  of  sand  and  clay  have  a 
specific  gravity  of  about  2.6  ;  they  are  therefore  held  in  suspension  only 
by   virtue    of    the    currents    maintained    in    the    water.     When   these 
currents  become  retarded  the  suspended  matter  is  gradually  deposited, 
the  rate  of    settling  varying  with  the  size  and  form  of   the   particles. 
The  weights  of  similar  particles  are  proportional  to  the  cubes  of  their 
diameters,  while    the  surface  areas  are   proportional    to  their  squares ; 
consequently  the  relative  resistance  to  sedimentation  is  much  greater 
with  fine  particles  than  with  coarse.     Very  weak  currents  may  be  suffi- 
cient   to  hold  fine   particles  in  suspension,  while    the  coarser  material 
readily  settles.     To   cause  the  deposition  of  the  finer  sediment   it   is 
therefore  necessary  for  the  water  to  be  brought  as  nearly  as  possible 
to  a  state  of  rest.     In  the  case  of  the  Missouri  and  Mississippi  River 
waters,  and  those  of  similar  clay-carrying  streams,  complete  clarification 
by  simple  sedimentation  is  impossible  at  certain  seasons  of   the  year, 
owing  to  the  extremely  attenuated  and  colloidal  character  of  the  clay 
particles.    This  condition  of  the  clay  is  considered  by  some  as  approach- 
ing the  condition  of  solution,  —  requiring  at  least  some  agglomeration 
or  coagulation  before  sedimentation  can  take  place.     Water  from  the 
Covington,  Ky.,  reservoir  which  had  settled  about  30  days  was  found  by 
Fuller  to  contain  as  high  as  50  parts  per  million  of  clay. 

466.  Time  Required  for  Subsidence.  —  The  time  required  for  satis- 
factory sedimentation   is   very  different    for    different   waters,   and   to 
determine  this  period  recourse  must  be  had  to  actual  experiments.     For 
some  waters  it  requires  weeks  and  even  months  to  remove  all  the  tur- 


PLAIN  SEDIMENTATION. 


427 


bidity,  while  for  others  a  settlement  of  a  day  or  two  accomplishes  fairly 
good  results.  If  the  amount  of  suspended  matter  is  measured  by 
weight,  a  large  proportion  will  settle  in  one  or  two  days  ;  but  the 
reduction  in  turbidity  is  not  correspondingly  great,  as  it  is  the  finer  por- 
tions which  exert  the  greatest  influence  upon  the  appearance  of  a  water. 
When  the  purpose  of  plain  sedimentation  is  to  prepare  the  water  for 
further  treatment,  a  high  degree  of  clarification  is  not  needed,  it  being 
more  economical  to  perfect  the  process  by  other  means.  The  best  period 
of  sedimentation  will  thus  depend  upon  the  character  of  the  raw  water 
and  the  relation  of  the  sedimentation  to  the  operation  of  the  entire  plant. 
For  plain  sedimentation  a  period  of  24  hours'  subsidence  is  about 
the  minimum  limit  adopted,  although  in  some  cases  a  still  shorter 
period  may  be  advisable.  At  Cincinnati  it  is  planned  to  allow  about 
three  days,  the  treatment  being  intended  as  a  preparation  for  filtration. 
The  rate  of  improvement  at  Cincinnati  is  indicated  by  the  results  of 
some  experiments  on  small  settling-tanks.  The  average  removal  of  sus- 
pended matter  was  as  follows  :* 


Time  of  Subsidence. 

24  hours  ...................  62  per  cent. 

48      «      ..................  68       « 

72      "      ..................  72       " 

96      "      ..................  76       " 


The  percentage  of  removal  was  greatest  when  the  amount  of  suspended 
matter  was  greatest. 

At  Louisville,  Fuller  concludes  that  the  economical  limit  of  plain 
subsidence  is  about  24  hours,  during  which  time  75  per  cent  of  the 
suspended  matter  is  removed.  Further  preparation  is  there  deemed 
necessary  for  filtration.  At  Kansas  City  about  83  per  cent  of  the 
suspended  matter  is  removed  by  24  hours'  subsidence. 

At  New  Orleans  the  sediment  is  unusually  fine,  average  results 
obtained  by  the  experiments  of  Weston  being  as  follows  :  f 


Period  of  Sub- 
sidence hours. 

Suspended  Matter. 

Parts  per  Million. 

Per  cent  Removed. 

0 
12 
24 
48 
72 

650 

435    ' 
360 

300 
265 

0 

33 
45 
54 
59 

*  Report  on  Water  Purification  at  Cincinnati,  p.  126. 
t  Report  on  Water  and  Sewage,  1903,  p.  101. 


428 


SEDIMENTATION  AND    COAGULATION. 


In  this  report  it  was  proposed  to  use  rapid  filters  with  alum  as  a 
coagulant  and  it  was  estimated  that  for  such  purpose  the  economical 
period  of  plain  sedimentation  would  be  from  12  to  24  hours.  The 
plans  adopted,  however,  employ  sulfate  of  iron  and  lime,  partly  in  order 
to  effect  a  softening  of  the  water.  The  period  of  plain  sedimentation 
provided  for  is  only  about  one  hour. 

467.  Bacterial  Efficiency  of  Sedimentation.  —  In  discussing  the  bac- 
terial efficiency  of  plain  sedimentation,  it  must  be  remembered  that  any 
data  gathered  under  ordinary  conditions  may  possibly  be  misleading, 
as  in  the  case  of  natural  sedimentation  in  lakes,  because  of  the  opera- 
tion of  other  factors,  such  as  light,  etc.,  that  may  also  act  as  more  or 
less  effective  agents  in  purification.  The  effect  of  sedimentation  alone 
can  be  most  accurately  determined  by  considering  the  phenomenon  as 
occurring  in  covered  reservoirs  where  the  direct  disinfecting  action  of 
light  and  its  indirect  effect  as  modifying  the  development  of  algae  might 
be  excluded.  This  condition  precludes  the  study  of  the  question  on  a 
large  scale,  as  it  is  impracticable  to  cover  reservoirs  that  are  large 
enough  to  permit  of  storage  for  a  considerable  period  of  time.  In  lieu  of 
any  data  under  these  conditions  reference  must  needs  be  made  to  studies 
on  sedimentation  in  open  reservoirs.  The  conclusions  drawn  from  such 
studies  are  strictly  applicable  only  to  reservoirs  under  like  conditions. 

The  monthly  results  obtained  by  the  Chelsea  Water  Company  of  Lon- 
don in  1896  are  given  in  Table  No.  61.*  (Time  of  storage  twelve  days.) 

TABLE    NO.    61. 

BACTERIAL   EFFICIENCY   OF   STORAGE   AND   FILTRATION,    CHELSEA   WATER   CO.,    LONDON. 


Month. 

Bacteria  per  Cubic  Centimeter. 

•  River  Thames. 

After  1  2  days' 
Storage. 

After 
Filtration. 

January 

11,560 
26,800 
18,000 
7,520 
2,060 
6,760 
2,220 
1,740 

4>3°° 

39,760 
8,560 

160,000 

1360 
460 
240 

140 
1150 
420 
2OO 
140 
340 
280 
854 

20 

44 
28 

4 
24 
I78 
20 
18 

2 

8 

12 

55 

February         

March      

April     

IVtay 

Tune                         ... 

Tulv 

August     

October 

November 

December   

Average   

24,107 

508 

34 

Average  percentage  reduction  by  subsidence,  97.85. 
Average  percentage  reduction  by  subsidence  and  filtration,  99.86. 
Results  obtained  by  other  London  works  ranged  from  49  to  85  per  cent  average 
reduction  for  periods  of  subsidence  varying  from  3.3  to  15  days. 

*  Hill.     Public  Water-supplies,  1898,  p.  144. 


PLAIN  SEDIMENTA  TION. 


429 


The  effect  of  the  time  factor  in  sedimentation  is  more  clearly  seen 
by  reference  to  the  data  given  in  Table  No.  62  relating  to  experiments 
made  at  the  St.  Louis  settling-basins.* 

TABLE  NO.  62  —  BACTERIAL  RESULTS  OF  STORAGE  AT  ST.  LOUIS. 


Time  of  Standing. 

No.  of  Bacteria  per  c.  c.  at  Different  Depths. 

2.5  Feet. 

5  Feet. 

7-5  Feet. 

o               .        

6510 
6290 
230 

200 

1970 
2990 
320 

200 

2960 
880 
200 
200 

x    ,  J 
2  days 

3  days      .  '  

The  effect  of  long  subsidence  is  shown  by  the  following  typical 
figures  relating  to  the  number  of  bacteria  in  the  Ohio  River  water  as 
supplied  to  Cincinnati,  Ohio,  and  to  Covington,  Kentucky.  In  Cin- 
cinnati the  water  had  little  or  no  sedimentation,  while  at  Covington  the 
large  reservoir  furnished  about  30  days'  subsidence.! 

TABLE  NO.  63. —  BACTERIAL  RESULTS  OF  STORAGE  AT  CINCINNATI  AND  COVINGTON. 


Bacteria  per  Cubic  Centimeter. 


Date. 

Cincinnati. 

Covington. 

.Reduced  by 
Sedimentation, 
Per  cent. 

January  23,  1896  

I  COO 

IQ4 

87.87 

February  4,  1897  .    

I6C.6 

C2 

96.80 

February  17,  1897     

684 

20 

97.08 

February  26,  1897     

I436 

102 

92  .  90 

An  experiment  on  the  efficiency  of  plain  sedimentation  was  carried  out 
by  Mr.  J.  W.  Hill  upon  one  of  the  divisions  of  the  Fairmount  Park  Res- 
ervoir, Philadelphia,  having  a  capacity  of  3,346,000  gallons.  Raw  water 
from  the  Schuylkill  River  was  pumped  in  and  allowed  to  rest  for  three 
to  four  weeks.  Results  of  two  such  experiments  were  as  follows  :  \ 


Days'  Subsidence. 

Test  No.  2. 

Test  No.  3 

Turbidity,  Parts 
per  Million. 

Bacteria, 
No.  per  c.  c. 

Turbidity,  Parts 
per  Million. 

Bacteria, 
No.  per  c.  c. 

Raw  water. 

9° 

24,000 

12 

5700 

5 

35 

18,500 

IO 

145° 

8 

25 

2650 

10 

500 

n 

3° 

400 

10 

145 

14 

25 

400 

12 

35 

17 

3° 

415 

9 

45 

20 

35 

250 

9 

60 

21 

15 

63 

24 

35 

975 

*  New  York  State  Board  of  Health  Report,  1893,  p.  711. 

t  Report  of  Engineer  Commission  of  Cincinnati  Water- works,  1896,  p.  15. 

J  Jour.  Assn.  Eng.  Soc.  1903,  xxx.  p.  246. 


430 


SEDIMENTATION  AND   COAGULATION. 


At  Cincinnati  Fuller  found  in  his  experiments  that  about  75  per 
cent  of  the  bacteria  were  removed  by  three  days'  subsidence.*  On  the 
other  hand  the  experiments  at  New  Orleans  showed  very  little  effect 
upon  the  bacterial  content  of  Mississippi  River  water  after  from  12  to  72 
hours'  subsidence. 

Notwithstanding  there  is  a  marked  degree  of  purification  from  long 
periods  of  subsidence,  yet  it  should  be  kept  in  mind  that  such  a  method 
of  purification  is  extremely  hazardous,  especially  where  the  water-supply 
is  subject  to  any  sewage-pollution.  This  is  strikingly  shown  in  the  case 
of  the  Lawrence  reservoirs  that  used  to  hold  from  10  to  14  days'  sup- 
ply and  in  which  there  was  a  reduction  of  about  90  per  cent  of  the 
bacteria  present  in  the  river-water ;  still  such  purification  was  insuffi- 
cient to  protect  the  supply,  as  is  evidenced  by  the  fact  that  the  typhoid 
death-rates  of  this  town  were  exceptionally  high  for  many  years. 

468.  Bacterial  Content  of  Reservoir  Sediment.  —  It  must  be  remem- 
bered that  while  subsidence  removes  bacteria  from  the  water,  it  is  only 
to  accumulate  them  in  relatively  larger  quantities  in  the  mud  and  ooze 
at  the  bottom  of  the  reservoir  (Art.  180).  Not  only  do  they  accumu- 
late here  from  deposition  from  superincumbent  waters  but  actual  growth 
occurs  in  abundance  in  the  rich  organic  matter  of  lake  bottoms. 
Russell  f  found  the  germ  content  in  the  water  and  mud  of  the  bay  of 
Naples  to  be  as  given  in  Table  No.  64 : 

About  one-half  of  the  species  present  in  the  mud  were  indigenous 
to  this  habitat,  while  the  remainder  were  common  to  both  water  and 
mud.  He  finds  that  the  same  principle  also  obtains  in  waters  of  fresh- 
water lakes.  In  the  layer  of  ooze  taken  from  the  reservoirs  of  the 
Altona  Water-works,:):  which  is  supplied  with  Elbe  River  water,  there 
were  found  17,000,000  bacteria  per  c.c.,  while  the  water  just  over  this 
slime  had  upwards  of  1,000,000  for  same  volume.  § 

TABLE   NO.    64. 

BACTERIA   IN    WATER    AND    MUD    OF    BAY    OF    NAPLES. 


Depth  of  Water. 

No.  of  Bacteria  per  Cubic  Centimeter. 

Meters. 

In  Water. 

In  Mud. 

5° 

121 

245,000 

100 

10 

200,000 

2OO 

59 

70,800 

300 

5 

24,OOO 

40O 

3° 

22,000 

500 

22 

12,500 

1  100 

24,OOO 

*  Fuller.     Cincinnati  Report,  p.  128.  f  Zeit.  f.  Hyg.,  1891,  xi.  p.  177. 

\  Cent.f.  Bakt.,  1898,  xvi.  p.  88 1. 

§  See  also  Lortet,  Pathogenic  Bacteria  in  Mud  of  Geneva  Lake.     Cent.  f.  Bakt., 
1891,  ix.  p.  709. 


SEDIMENTATION   WITH  COAGULATION. 


431 


469.  Experimental  Data  on  the  Action  of  Finely  Divided  Matter  in 
Water.  — Abundant  experience  has  demonstrated  the  value  of  copious 
amounts  of  suspended  matter  in  purifying  waters  by  sedimentation. 
In  the  light  of  this  fact,  the  following  experiments  made  by  Frankland  * 
are  of  interest  in  showing  the  value  of  different  solids  in  purifying  water 
by  agitation  and  subsequent  subsidence.  These  trials  were  confined 
for  the  most  part  to  laboratory  conditions,  but  they  illustrate  the  prin- 
ciple involved  in  this  type  of  purification.  Water  was  shaken  up  for  a 
definite  length  of  time  with  finely  divided  sterilized  material  of  uniform 
size  and  then  allowed  to  clarify  itself  by  sedimentation.  The  clear 
supernatant  water  was  then  examined  bacteriologically  with  the  results 
given  in  Table  No.  65. 

TABLE    NO.    65. 

PURIFICATION   OF    WATER   BY   AGITATION   WITH    FINELY   DIVIDED   SOLID   MATTER   AND 
SUBSEQUENT    SUBSIDENCE. 


Spongy 
Iron. 

Chalk. 

Animal 
Charcoal. 

Vegetable 
Charcoal. 

Coke. 

Amt.  of  suspended  matter  (by  wgt.) 
No.  of  bacteria  per  c.c.  before  treat- 
ment 

1:10 
600 

1:50 
8000 

1:50 
8000 

1:50 

•2OOO 

1:50 
verv 

No.   of  bacteria  per  c.c.   after  treat- 
ment for  15  minutes    
Percentage  reduction  

63 
no 

270 
07 

60 
00 

120 
06 

large 
o 

IOO 

SEDIMENTATION    WITH    COAGULATION. 

470.  The  Use  of  Coagulants.  —  Various  chemicals  when  added  to 
water  will  combine  with  certain  substances  ordinarily  present,  forming 
precipitates  which  are  more  or  less  gelatinous  in  character.  These 
act  as  coagulants  to  collect  the  finely  divided  suspended  matter  into 
relatively  large  masses  which  are  thus  much  more  readily  removed  by 
sedimentation  or  filtration.  Color  may  also  frequently  be  removed  to 
a  large  extent  by  this  treatment.  The  use  of  coagulants  in  water 
purification  was  at  first  almost  entirely  confined  to  their  employment  in 
connection  with  rapid  filters  (see  Chapter  XXII),  but  the  great  advan- 
tage of  their  use  in  connection  with  the  subsidence  of  turbid  waters 
makes  them  of  value  whatever  the  subsequent  process  may  be.  In 
some  notable  instances  sedimentation  thus  aided  has  been  found  to  be 
sufficient  without  further  treatment.  Where  waters  are  very  turbid  it 
will  usually  be  more  economical  to  allow  the  coarser  sediment  to  settle 


*  Proc.  Roy.  Soc.,  1885.     Proc.  Inst.  C.  E.  1886,  LXXXV.  p.  197. 


432  SEDIMENTA  TION  AND    COAG ULA  TION. 

before  the  application  of  a  coagulant,  as  in  this  way  the  amount  of 
chemical  required  is  much  reduced.  Occasionally,  also,  double  sedimen- 
tation with  the  use  of  coagulants  in  both  cases  may  be  advisable. 

471.  The  Action  of  Various  Coagulants. —  Sidfate  of  Alumina. — 
Several  substances  can  be  used  as  coagulants.  That  most  commonly 
employed  is  sulfate  of  alumina.  When  this  substance  is  introduced 
into  water  containing  carbonates  and  bicarbonates  of  lime  and  magnesia, 
it  is  decomposed,  the  sulfuric  acid  forming  sulfates  with  the  lime  and 
magnesia,  while  the  carbonic  acid  is  set  free,  and  the  alumina  unites 
with  water  to  form  a  bulky  gelatinous  hydrate  which  constitutes  the 
coagulating  agent.  According  to  Fuller,  part  of  this  hydrate  may  be 
absorbed  by  the  clay  particles  before  much  coagulating  action  takes 
place,  the  amount  absorbed  depending  upon  the  amount  and  character 
of  the  sediment.  If  more  sulfate  is  used  than  can  combine  with  the 
quantity  of  carbonates  present,  it  will  remain  dissolved  in  the  water,  a 
result  which  is  necessary  to  avoid  on  account  of  the  possible  injurious 
effect  of  the  alum.  If  the  water  does  not  naturally  contain  a  sufficient 
amount  of  alkalinity  to  decompose  the  necessary  amount  of  coagulant, 
lime  should  be  previously  added  to  the  water.  Theoretically,  one  grain 
of  sulfate  will  decompose  about  8  parts  per  million  of  CaCO3  or  its 
equivalent,  but  owing  to  the  absorptive  action  previously  mentioned  the 
actual  reduction  of  alkalinity  is  likely  to  be  less.  Experiments  at 
Louisville  and  at  New  Orleans  indicate  a  reduction  of  alkalinity  of  from 
65  to  90  per  cent  of  the  theoretical  amount.  It  was  also  shown  that 
much  more  coagulant  was  required  with  fine  sediment  than  with  coarse. 

Accompanying  the  reduction  of  the  carbonates  is  an  equal  increase 
in  the  sulfates  of  lime  and  magnesia.  As  these  compounds  form  the 
objectionable  incrusting  constituents  or  the  permanent  hardness  of  a 
water,  this  change  is  detrimental.  With  the  ordinary  quantities  of 
coagulant  used,  such  as  I  to  2  grains  per  gallon,  this  increase  in  hard- 
ness would  amount  to  from  9  to  18  parts  per  million,  not  relatively  a 
very  important  matter,  and  probably  much  overbalanced  by  the  gain 
in  clearness  of  the  water.  This  objectionable  increase  in  the  permanent 
hardness  may  be  avoided  by  the  use  of  sodium  carbonate  instead  of 
lime  (Art.  558). 

The  amount  of  carbonic  acid  set  free  is  equal  to  44  per  cent  of  the 
decrease  in  carbonates.  This  acid  remains  absorbed  in  the  water  and 
increases  its  corrosive  action  on  unprotected  iron  plates,  which  is,  how- 
ever, not  a  serious  matter.  If  the  carbonate  is  all,  or  nearly  all  reduced, 
there  is  more  danger  of  solvent  action  on  lead  pipes. 

Iron.  —  Since  about  1903  the  use  of  iron  as  a  coagulant  has  been 


THE    USE  OF  COAGULANTS.  433 

rapidly  developed.  Ferric  hydrate  has  long  been  known  to  be  an 
effective  coagulant,  acting  in  a  manner  similar  to  the  aluminum  hydrate. 
Ferric  hydrate  can  readily  be  produced  by  the  use  of  ferric  sulfate,  but 
this  is  impracticable  on  account  of  the  expense  involved.  Another  way 
of  obtaining  this  hydrate  is  by  the  use  of  metallic  iron,  as  in  the 
Anderson  process  described  later  (Chapter  XXIII).  In  this  case  the 
metallic  iron  forms  ferrous  carbonate  with  the  carbonic  acid  present, 
which  in  turn  oxidizes  to  the  ferric  hydrate  from  the  oxygen  dissolved 
in  the  water. 

More  recently  the  iron  solution  has  been  furnished  by  the  direct 
absorption  of  fumes  of  burning  sulphur  by  water  containing  scrap-iron. 
This  process,  patented  by  the  Jewell  Filter  Company,  has  been  success- 
fully used  in  several  plants  in  the  Middle  West.  A  still  more  promising 
method  and  one  now  (1908)  in  successful  use  in  several  places,  notably 
at  St.  Louis,  is  the  use  of  ferrous  sulfate  and  caustic  lime  in  the  form 
of  milk  of  lime.  In  this  process,  as  in  the  alum  process,  the  sulfuric 
acid  unites  with  the  lime  and  magnesia  present  forming  soluble  sul- 
fates.  Without  the  addition  of  caustic  lime  the  iron  would  form  a 
carbonate  which  would  change  to  the  hydrate  but  slowly.  The  lime 
unites  with  the  free  CO2  present  thus  greatly  hastening  the  process, 
and  at  the  same  time  precipitating  part  of  the  lime  present,  CaCO3,  in 
same  manner  as  in  the  lime  softening  process.  (See  Chapter  XXIII.) 
Very  soft  waters  require  a  more  exact  proportioning  of  chemicals  than 
waters  somewhat  hard,  as  in  the  latter  case  any  excess  of  lime  serves 
only  to  partially  soften  the  water.  Waters  containing  vegetable  color- 
ing matter  are  likely  to  give  trouble  by  retaining  the  iron  in  solution  in 
the  same  manner  as  certain  ground-waters  which  contain  iron.  (See  Art. 
563.)  In  the  case  of  hard  waters  the  element  of  softening  may  become 
an  important  feature  and  the  amount  of  lime  increased  to  attain  this 
object.  This  needs  to  be  done  with  caution  as  the  resulting  precipitate 
of  CaCO3  is  likely  to  be  troublesome  to  deal  with  because  of  its  ten- 
dency to  clog  pipes  and  channels. 

The  ferric  hydrate  seems  to  be  quite  as  efficient  a  coagulating 
agency  as  aluminum  hydrate,  and  as  its  cost  is  considerably  less,  the 
iron  and  lime  process  is  likely  to  be  more  economical  in  those  waters 
where  experiments  show  that  it  can  be  used  with  success.  On  the  other 
hand,  sulfate  of  aluminum  appears  to  be  of  more  general  applicability 
for  waters  of  all  kinds. 

Other  Coagulating  Agencies.  —  Both  the  aluminum  and  the  ferric 
hydrate  can  be  produced  electrolytically  from  the  metals.  The  expense 
of  metallic  aluminum  as  compared  to  the  sulfate  precludes  the  use  of 


434  SEDIMENTATION  AND   COAGULATION. 

that  metal,  but  it  is  possible  that  in  some  cases  the  ferric  hydrate 
might  be  economically  produced  in  this  way.  (For  further  discussion 
see  Chapter  XXIII.) 

Lime  is  another  substance  that  may  be  used  as  a  coagulant.  When 
used  in  the  ordinary  Clark  process  for  softening  water  the  effect  is  con- 
siderable, but  still  greater  effects  can  be  obtained  by  using  lime  in 
moderate  excess.  Naturally  the  pulverulent  precipitate  of  lime  car- 
bonate is  generally  not  nearly  as  effective  as  the  gelatinous  alumina 
precipitate.  Experiments  involving  this  process  at  Cincinnati,  Ohio, 
showed  the  following  average  results  :  * 


River  Water. 

Effluent. 

Per  cent 
Removed. 

Suspended  matter  (parts  per  1,000,000) 

273 
23,800 

35 

I  ^OO 

87.  2 
04-  ^ 

The  average  period  of  subsidence  was  about  14  hours,  and  the 
average  amount  of  lime  used  was  4.7  grains  per  gallon,  of  which  3.1 
grains  was  in  excess  of  the  amount  required  to  combine  with  the 
bicarbonates.  This  excess  of  lime  involves  a  further  process  for  its 
removal,  which  may  consist  in  the  addition  of  carbonic  acid. 

In  some  cases  the  coagulating  agent,  if  added  in  large  quantities, 
produces  not  only  the  mechanical  effect  of  sedimentation  due  to  the 
settling  of  the  precipitate,  but  the  excess  of  chemical  used  may  act  as 
a  direct  germicide  on  the  bacteria  present.  Such  treatment,  however, 
is  inapplicable  for  water-purification,  although  it  is  sometimes  used  in 
the  treatment  of  sewage. 

472.  The  Amount  of  Chemical  Required.  —  This  depends  upon  the 
amount  and  character  of  the  sediment,  upon  the  degree  of  purification 
desired,  and  upon  the  time  of  settlement.  It  varies  in  practice  from 
about  |  grain  to  3  or  4  grains  of  sulfate  per  gallon.  The  proper 
amount  can  only  be  determined  by  experiment.  Some  idea  of  the 
amount  required  can  be  had  from  the  data  of  Table  No.  66.  This  gives 
the  approximate  amount  of  chemical  required  for  the  Ohio  River  water 
at  Cincinnati,!  the  Allegheny  River  water  at  Pittsburg4  and  the  Mis- 
sissippi River  water  at  New  Orleans,  §  as  a  preparation  for  filtration. 
In  general  the  more  chemical  used  the  greater  the  effect,  and  by  using 
a  sufficient  quantity  and  allowing  enough  time  for  sedimentation  a 

*  Cincinnati  Report,  p.  483. 

t  Cincinnati  Report,  pp.  290,  341. 

$  Report  of  the  Pittsburg  Filtration  Commission,  1899. 

|  Report  on  Water  and  Sewerage,  1903,  p.  130. 


AMOUNT  OF  CHEMICAL   REQUIRED. 


435 


clear  water  can  be  secured.  But  the  question  of  economy  will  usually 
limit  the  efficiency  obtained,  and  where  the  process  is  but  a  preliminary 
treatment  a  high  degree  of  efficiency  is  not  necessary.  At  New  Or- 
leans it  is  estimated  by  Weston  that,  with  a  preliminary  period  of  sedi- 
mentation of  twelve  hours,  an  amount  of  coagulant  should  be  used 
sufficient  to  reduce  the  suspended  matter  to  about  forty-five  parts, 
requiring  a  maximum  of  about  twelve  hours  further  sedimentation. 
This  treatment  is  supposed  to  be  followed  by  rapid  filtration. 

TABLE    NO.  66. 

ESTIMATED    AVERAGE    AMOUNTS    OF    REQUIRED    CHEMICAL    FOR    DIFFERENT    GRADES 

OF    WATER. 


Sulfate  of  Alumina  Required,  Grains  per  Gallon. 

Suspended 

Matter, 

Raw  Water 

SubsidedWater 

SubsidedWater 

Minimum  for 

SubsidedWater 

Unsubsided 

Parts 

for  Sand 

for  Sand 

for  Rapid 

Raw  Water  for 

for  Rapid 

Water  for 

per 

Filters, 

Filters, 

Filters, 

Rapid  Filters, 

Filters, 

Rapid  Filters, 

Million. 

Cincinnati. 

Cincinnati. 

Cincinnati. 

Pittsburg. 

New  Orleans. 

New  Orleans. 

10 

0 

0 

°-75 

0.40 

.  .  . 

.  .  . 

25 

0 

0 

1.25 

0.50 

5° 

o 

O 

I.SO 

O.  70 

1.70 

75 

0 

1.30 

C-95 

0.90 

1.85 

IOO 

1-5° 

I.  60 

2.20 

.00 

2.  IO 

125 

I.  60 

I.  80 

2.45 

•!5 

2.30 

150 

1.70 

2.00 

2.65 

•3° 

2-45 

3.00 

175 

I.  80 

2.  IO 

2.85 

.40 

2.60 

3-15 

2OO 

i-95 

2.20 

3.00 

.60 

2.70 

3-3° 

300 

2.25 

2-45 

3.80 

2.OO 

3-40 

3-95 

4OO 
500 

2.50 
2.80 

2-75 

4.40 

2.50 

4.  10 

4-65 
5-65 

600 

3-°5 

6.30 

75° 

3-40 

7-45 

1000 

4.00 

10.  15 

1200 

4-75 



The  amount  required  for  the  Missouri  River  water  at  Kansas  City, 
where  sedimentation  is  the  only  purification  employed,  is  given  by 
Kiersted  as  follows : 

AMOUNT  OF  CHEMICAL  REQUIRED   FOR  THE   CLARIFICATION   OF  THE   MISSOURI  RIVER   WATER. 


Suspended  Matter  after 
24  hours  Natural 
Subsidence,  Parts  per 
Million. 

Sulfate  of  Alumina 
Required  for  Clarifica- 
tion, Grains  per 
Gallon. 

Suspended  Matter  after 
24  hours  Natural 
Subsidence,  Parts  per 
Million. 

Sulfate  of  Alumina 
Required  for  Clari- 
fication, Grains  per 
Gallon. 

5° 

IOO 

IS® 

200 
250 

300 

O.o 

0-5 
1.0 

i-5 
1.9 

2.4 

350 
400 

.     450 
500 

55° 
600 

2.9 
3-4 
3-8 
4-3 
4.8 

5-3 

*  Waterworks  Management  and  Maintenance,  p.  148. 

436 


SEDIMENTATION  AND   COAGULATION. 


The  water  is  subjected  to  preliminary  natural  sedimentation  for  24 
hours.  For  less  than  50  parts  suspended  matter  per  million  no  further 
clarification  is  required. 

At  St.  Louis  iron  and  lime  are  used  without  preliminary  sedimenta- 
tion. The  average  amounts  used  in  1906-7  were  2.13  grains  sulfate 
of  iron  and  7.39  grains  of  lime.  The  average  amount  of  suspended 
matter  is  about  1200  parts  per  million. 

The  following  is  an  estimate  by  Ellms  of  the  amounts  of  iron  and 
lime  required  for  the  Ohio  River  water  at  Cincinnati  as  compared  to 


alum/ 


AMOUNT   OF   CHEMICALS    REQUIRED    FOR   THE   PURIFICATION   OF    SUBSIDED 
OHIO    RIVER    WATER. 


Sulfate  of  Iron  and  Lime. 

Turbidity, 

Sulfate  of  Alumina, 

Parts  per  Million. 

Grains  per  Gallon. 

Sulfate  of  Iron, 

Caustic  Lime, 

Grains  per  Gallon. 

Grains  per  Gallon. 

IO 

o-75 

1.  00 

0-75 

25 

1.25 

1.25 

0.90 

5° 

1.50 

.40- 

.OO 

75 

i-95 

•5° 

.IO 

100 

2.  2O 

.60 

.20 

125 

2-45 

•75 

•3° 

15° 

2.65 

.90 

.40 

175 

2.85 

2.10 

•So 

200 

3.00 

2.25 

.70 

300 

3.80 

2.50 

.90 

400 

4.40 

3.00 

2.0O 

473.  Time  of  Subsidence.  —  The  rate  of  sedimentation  depends 
greatly  upon  the  amount  of  coagulant  employed.  It  takes  place  much 
more  quickly  than  where  no  coagulant  is  used,  so  that  a  large  part  of 
the  action  will  occur  in  a  few  hours.  Where  the  process  is  preliminary 
to  rapid  filtration  the  period  allowed  is  usually  from  two  to  six  hours. 
In  this  case  it  is  not  desired  that  perfect  clarification  shall  be  secured, 
as  better  results  will  be  obtained  from  the  filters  if  a  small  amount  of 
the  flocculent  coagulant  be  carried  over  to  the  filters  ;  but  too  large  an 
amount  of  sediment  increases  the  cost  of  filtration  more  than  the 
decrease  in  cost  of  sedimentation.  At  New  Orleans,  where  the  sedi- 
ment is  very  fine,  a  period  of  twelve  hours  is  estimated  by  Weston  to 
be  somewhat  more  economical  considering  the  entire  process  than  six 
hours,  but  the  difference  is  not  great.  The  new  plant  provides  for 
about  six  hours  using  iron  and  lime.  At  St.  Louis,  where  the  process 
is  final,  the  total  capacity  of  the  series  of  basins  is  about  two  days' 

*  Eng.  Record,  1906,  LIV.  p.  441. 


EFFICIENCY  OF  SEDIMENTATION   WITH  COAGULATION,         437 


supply.  This  is  now  (1908)  being  increased  by  50  per  cent  by  the  con- 
struction of  two  additional  basins.  The  question  of  amount  of  chemical 
needed,  time  of  subsidence  and  degree  of  purification  desired  are  inti- 
mately related,  and  the  best  and  most  economical  arrangement  must  be 
worked  out  for  each  case  individually. 

474.  Efficiency  of  Sedimentation  with  Coagulation.  —  As  previously 
stated,  the  efficiency  is  a  function  of  the  time,  amount  of  coagulant,  and 
character  of  the  sediment.  The  bacterial  efficiency  follows  in  a  general 
way  the  efficiency  with  respect  to  the  suspended  matter.  Where  used 
as  a  preliminary  process  there  is  usually  no  difficulty  in  securing  a 
sufficient  degree  of  clarification  in  a  few  hours,  either  with  or  without 
preliminary  natural  sedimentation,  the  only  question  being  that  of 
amount  of  coagulant  and  cost  of  operation.  As  already  stated,  the 
amount  of  suspended  matter  which  may  economically  be  left  to  be 
taken  care  of  by  the  filters  is  estimated  at  30  to  45  parts  per  million  at 
New  Orleans ;  at  Cincinnati  Mr.  Fuller  considered  it  advisable  to  apply 
further  preparatory  treatment  than  plain  sedimentation  where  the 
amount  of  sediment  exceeded  40  or  50  parts  per  million.  Where  the 
process  is  final  the  absolute  efficiency,  both  with  respect  to  suspended 
matter  and  bacteria,  is  of  great  importance.  Ordinarily,  with  waters 
containing  clay,  it  will  be  difficult  to  reduce  the  suspended  matter 
below  20  parts  per  million  in  a  reasonable  time.  Probably  the  most 
successful  plant  in  this  respect  is  that  at  St.  Louis.  Here  the  water  is 
treated  with  iron  and  lime  and  flows  through  a  series  of  six  basins 
originally  operated  for  plain  sedimentation.  The  average  results  for  a 
year  are  as  follows  in  parts  per  million  : 


River. 

Treated  Water. 

Solids  in  suspension    

1188 

3  8 

Color   

43 

IO   7 

Alkalinity    

13^ 

40 

Calcium                      .    .                           . 

42    \ 

ny 

22    8 

Magnesium     ..       . 

<M  •  v) 

•\-y     T 

4c* 

•  j 

A  relatively  large  amount  of  lime  was  used,  thus  causing  a  consider- 
able softening  effect.  The  average  results  for  March,  1907,  were  as 
follows : 


River. 

Weir  i. 

Weir  3. 

Weir  5. 

Tap. 

Suspended,  matter    

1444 

14    2 

8    K 

e   S 

2     C6 

Color             

4^  .  3 

jf3  6 

"•oo 
1  3 

0  •  ° 
ii  6 

*  •0IJ 

10  8 

m 

ci  .  i 

47 

JtV 

41 

Bacteria  per  c  c 

<?7O2Q 

Q33 

COT 

0WA 

438  SEDIMENTA  TION  AND   CO  A  GULA  TION. 

The  several  "weirs"  are  the  effluent  weirs  of  the  several  basins 
operated  in  series.  The  very  high  results  obtained  with  reference  both  to 
the  suspended  matter  and  bacteria  are  noteworthy.  Further  data  show 
an  average  percentage  removal  of  bacteria  for  the  three  months,  Jan- 
uary, February  and  March,  1907,  of  98.87,  98.8  and  99.88  respectively, 
from  raw  water  to  tap.  This  result  is  quite  comparable  with  the  best 
filtration.*  These  results  as  to  bacteria  are  better  than  are  generally 
secured,  but  a  very  large  degree  of  purification  is  obtained  at  all  times. 

In  the  case  of  the  usual  sedimentation  of  two  to  six  hours  secured  in 
connection  with  rapid  filtration  the  reduction  in  bacterial  content  will 
usually  range  from  50  per  cent  to  as  high  as  90  or  95  per  cent.  The 
latter  figure  is  unusual  and  occurs  only  where  the  absolute  number  in 
the  raw  water  is  high.  Bacterial  examinations  of  water  from  the  set- 
tling-tanks connected  with  rapid  filters  at  Louisville  showed  a  removal 
in  the  very  short  time  there  allowed  for  sedimentation  (less  than  one 
hour)  of  ordinarily  from  40  to  75  per  cent  of  the  bacteria.  The 
removal  of  other  suspended  matter  was  scarcely  more  than  this.  When 
allowed  to  stand  overnight,  or  over  Sunday,  the  removal  of  bacteria  and 
suspended  matter  was  practically  always  over  90  per  cent.  With  large 
amounts  of  coagulant,  such  as  5  or  6  grains  per  gallon,  very  high 
efficiencies  may  be  reached. 

In  general  it  may  be  said  that  the  results  of  sedimentation  with 
coagulation  are  not  sufficiently  good  to  make  this  a  safe  process  to 
apply,  without  further  treatment,  to  a  sewage  polluted  stream,  although 
the  work  at  St.  Louis  indicates  that  under  certain  circumstances  very 
satisfactory  results  may  be  secured.  Many  waters  can  be  satisfactorily 
clarified  in  this  way,  but  in  the  case  of  some  waters  perfectly  satisfac- 
tory results  cannot  readily  be  secured  without  filtration. 

The  removal  of  color  depends  much  upon  the  nature  of  the  water. 
Usually  from  70  to  90  per  cent  of  the  color  of  ordinary  waters  may  be 
removed  by  suitable  quantities  of  chemical,  but  some  waters,  especially 
those  having  a  high  color,  cannot  readily  be  decolorized  in  this  way. 
At  Superior,  Wis.,  the  use  of  four  grains  of  sulfate  per  gallon  had  no 
appreciable  effect  on  a  water  having  a  color  of  about  2  on  the  platinum 
scale. 

SETTLING-BASINS. 

476.  Settling-basins  are  constructed  in  accordance  with  the  same 
general  principles  as  other  reservoirs ;  in  fact,  in  many  cases,  distribut- 
ing-reservoirs or  storage-reservoirs  act  also  as  settling-basins.  Where, 

*  See  valuable  paper  by  Edward  E.  Wall  on  "Water  Purification  at  St.  Louis, 
Mo.,"  in  Proc.  Am.  Soc.  C.  E.,  Sept.  1907,  p.  758.    Also  Eng.  Record,  1907,  LVI.  p.  98. 


NUMBER   AND  SIZE    OF  BASINS.  439 

however,  but  a  short  time  is  allowed  for  settling,  and  reservoirs  are 
intended  for  that  special  purpose,  there  are  differences  in  detail  which 
should  be  considered.  Settling-basins  are  usually  supplied  with  water 
by  means  of  low-service  pumps,  and  from  the  basins  the  water  flows 
into  an  equalizing  clear-water  reservoir,  or  to  a  pump-well,  or  to  filters, 
as  the  case  may  be. 

477.  Methods  of  Operation.  —  There  are  two   general  methods  of 
operating  settling-basins:  (i)  the  continuous-flow  method,  and  (2)  the 
intermittent    or   fill-and-draw    method.      In    the   former    the  water   is 
allowed  to  flow  at  a  very  slow  velocity  through  one  or  more  reservoirs, 
during  which  time  the  settling  takes  place.     In  the  latter,  the  water  is 
let  into  a  basin  and  allowed  to  remain  quiescent  during  the  period  of 
subsidence.     It  is  then  drawn  off  to  as  low  a  level  as  efficient  clarifica- 
tion has  taken  place,  and  the  basin  refilled.     The  method  of  fill-and- 
draw,   formerly  used  at   St.   Louis  for  plain   sedimentation,   has  been 
changed  to  the  continuous-flow  method  with  coagulation.     At  Cincin- 
nati, Ohio,  the  fill-and-draw  method  is  used,  but  it  is  stated  that  this  is 
on  account  of  matters  pertaining  to  the  form  of  the  basins  which  are 
purely  local  in  character.     In  the  fill-and-draw  method  no  settlement  of 
fine  particles  can  commence  until  the  operation  of  filling  is  completed, 
which  condition  materially  reduces  the  time  of    subsidence.     On  the 
other  hand  the  water  becomes  more  quiet  than  in  the  other  process, 
and  this  operates  to  its  advantage. 

Independent  of  the  question  of  clarification,  a  disadvantage  of  the 
intermittent-flow  method  is  in  the  loss  of  head  occasioned  by  its  use. 
Thus  the  highest  level  of  the  water  in  the  clear- water  basin  or  in  the 
filters  must  be  as  low  as  the  lowest  point  at  which  the  water  is  drawn 
off.  This  not  only  increases  the  expense  of  pumping,  but  is  an 
arrangement  not  always  easy  to  make.  In  the  continuous-flow  system 
practically  no  head  need  be  lost  in  the  settling-basins.  It  should  be 
noted,  however,  that  basins  on  the  fill-and-draw  method  can  be  utilized 
more  or  less  as  storage-reservoirs,  which  cannot  be  done  with  the 
others.  This  gives  more  elasticity  to  the  system  and  admits  of  a  freer 
operation  of  the  supply-pumps. 

Generally  speaking  the  continuous-flow  system  is  the  more  advan- 
tageous and  is  the  system  now  almost  universally  employed  where  the 
water  is  given  a  relatively  brief  period  of  sedimentation  with  the  aid  of 
a  coagulant. 

478.  Number  and  Size  of  Basins.  —  If  the  basins  are  operated  on  the 
continuous  system,  a  single  basin  can  be  made  to  suffice,  an  arrangement 
quite    suitable  for  a  relatively  clear  water  where  sedimentation  is  a 


44O  SEDIMENTATION  AND    COAGULATION. 

secondary  matter,  or  merely  a  preparation  for  filtration.  If  there  is 
much  sediment,  at  least  two  basins  are  needed,  in  order  that  one  may 
be  cleaned  without  interrupting  the  supply.  It  is  found  also  that 
generally  better  results  can 'be  obtained  by  the  use  of  two  or  three 
basins  in  series  than  by  the  use  of  a  single  one  of  the  same  total 
capacity.  While  this  effect  can  be  secured  by  inexpensive  partitions 
in  a  single  basin,  yet  convenience  in  the  removal  of  sediment  makes 
it  desirable  to  have  at  least  two  and  often  three  independent  basins. 
Where  a  coagulant  is  used  after  partial  sedimentation  at  least  three 
would  be  necessary  for  convenient  operation. 

With  the  fill-and-draw  method,  the  number  becomes  a  question  of 
economical  construction  and  operation.  The  basin  being  filled  is  not 
effective,  and  that  being  drawn  from  may  be  counted  as  one-half  effec- 
tive, so  that  if  q  is  the  capacity  of  each,  A  the  volume  of  consumption 
for  the  selected  time  of  settlement,  and  n  the  number  of  basins,  then 

^ 
n^  -  +  ij; 

9 

that  is,  the  required  number  is  equal  to  the  fixed  volume  A  divided  by 

the  capacity  q,  plus  i£.     The  larger  the  value  of  q,  the  lower  will  be 

^ 
the  cost  of  the    —  basins,  but  the  higher  will  be  the  cost  of  the  extra 

q 

ij  basins.  The  best  capacity  and  number  can  readily  be  determined 
by  trial  estimates.  At  St.  Louis,  the  best  number  was  found  to  be 
from  6  to  8. 

479.    Form  of  Basin. —  For  a  single  rectangular  basin  of  given  area 
the  square  is  the  most  economical  form.    For  a  number  of  basins  the 
best  proportions  may  be  determined  by  trial  esti- 
T   mates,  but  the  following   analysis  will  be  of  some 
^   assistance  in  arriving  at  an  approximate  solution  : 

Let  n  =  number  of  basins,  each  of  which  has  a 
•*•    width  b  and  length  a  (Fig.  117).      Let  ce  =  cost  per 
FlG>  II7'  lineal    foot    of   exterior  wall  or    embankment,  and 

c{  =  cost  of  interior  wall  or  embankment.  Then  if  C  =  total  cost  of 
embankments,  we  have 

£7=  (2nb+  2a)ce+  (n  —  \}aci (i) 

A 

Let   ab  =  Ay  a  constant  quantity.      Then   b  =  —      Substituting  this 

a 

value  in  the  above  equation,  we  have 

A 
C  =  (2n  -  +  2a)ce  +  («  —  1)04     ....      (2) 


ARRANGEMENT  OF  PIPES.  441 

Differentiating  with  respect  to  a,  equating  to  zero,  etc.,  we  find  that 
for  a  minimum  value  of  C  the  value  of  a  is 

2Hbce  b          2   +(«-0  J 

,  whence  -  =  -  $  .     .     .     (3) 


, 
2ce  +  (»—  iX/  a  2n 

If  ce  =  cif  then  -  =  -  ;  which  gives  for  n  =  2,  £  =  J  #;  for 
«  =  3>  <*  =  f  «i  etc. 

The  above  results  are  seen  to  be  independent  of  the  area,  and  hence 
are  true  for  basins  or  reservoirs  of  any  size,  arranged  in  the  manner 
shown. 

In  general,  settling-basins,  where  large,  are  built  similar  to  ordinary 
reservoirs,  partly  in  excavation  and  partly  by  embankment,  so  as  to 
secure  the  greatest  economy.  Earthern  slopes  will  usually  be  cheaper 
than  masonry  walls,  but  with  the  fill-and-draw  method  the  former  have 
the  disadvantage  of  exposing  the  mud  at  each  period  of  emptying. 
They  are,  however,  more  often  used.  Where  built  for  use  as  coagulating 
basins  in  connection  with  filters,  they  are,  in  the  case  of  small  plants, 
frequently  built  as  part  of  a  structural  unit,  being  made  with  masonry 
or  concrete  walls  and  possibly  floored  over. 

The  depth  of  basins  is  made  about  such  as  to  give  the  most  econom- 
ical construction,  very  shallow  basins  being  avoided.  The  time  of 
settlement  is  found  not  to  be  materially  affected  by  depth. 

480.  Arrangement  of  Pipes,  Continuous-flow  System.  —  The  object 
to  be  attained  in  this  system  is  the  distribution  of  the  water  on  entering 
as  evenly  as  may  be  across  one  side  or  one  end  so  that  it  shall  enter 
with  as  little  disturbance  as  possible  ;  then  to  draw  it  off  in  a  similar 
manner  from  the  opposite  side,  and  from  the  stratum  of  clearest  water. 
As  far  as  possible  all  parts  of  the  water  should  remain  in  the  basin 
equal  lengths  of  time,  and  all  strong  currents  should  be  avoided.  A 
common  form  of  inlet  consists  in  a  single  large  pipe  laid  through  the 
embankment,  or  a  single  sluice-gate  in  a  gate-chamber  built  in  the 
walls. 

A  much  better  distribution  of  the  water  is  obtained  by  means  of 
numerous  inlets,  or  numerous  branches  from  a  single  inlet  conduit,  and 
several  of  the  later  works  have  been  arranged  in  this  way.  For  this 
purpose  a  concrete  conduit  may  be  used,  built  within  the  reservoir,  or 
just  back  of  the  face,  and  provided  with  numerous  openings.  The 
maximum  uniformity  of  flow  will  usually  be  secured  if  the  water  is 


442  SEDIMENTATION1  AND    COAGULATION. 

admitted  near  the  bottom.  This  is  especially  the  case  in  summer  when 
the  entering  water  is  apt  to  be  cooler  than  the  surface  water  in  the 
reservoir. 

The  withdrawal  of  water  in  this  system  should  take  place  from  near 
the  surface.  Broad  weirs  formed  in  the  wall,  or  made  of  iron  troughs, 
are  frequently  used.  Instead  of  weirs,  a  series  of  vertical  pipes  open  at 
the  upper  end  may  be  used,  as  in  the  Albany  settling-basin  described  on 
page  467.  At  Denver  the  water  flows  off  over  a  very  large  number  of 
circular  weirs  fitted  to  vertical  effluent  pipes.  Outlet  conduits  of  con- 
crete, arranged  as  above  described  for  inlet  conduits,  constitute  a  con- 
venient arrangement.  (See  Art.  484,  for  example.) 

If  a  perfectly  uniform  movement  can  be  secured,  a  single  large  basin 
will  be  as  efficient  as  any  other  arrangement.  On  account,  however,  of 
the  effect  of  wind,  temperature  changes,  and  variation  in  flow,  in  causing 
irregular  currents,  and  hence  a  more  or  less  mixing  of  the  entire  con- 
tents of  a  single  reservoir,  there  are  some  advantages  in  separating  the 
process  into  parts  so  as  to  prevent  the  more  turbid  water  from  mixing 
with  the  less  turbid.  This  can  be  done  by  using  two  or  more  reservoirs 
in  series,  or,  less  perfectly,  by  placing  baffles  or  light  wooden  partitions 
in  a  single  reservoir,  or  by  constructing  a  single  reservoir  very  long  and 
narrow.  The  general  effect  of  such  arrangements  is  to  increase  the 
average  velocity  of  flow,  but  up  to  a  certain  point  the  effect  of  this 
increase  is  more  than  balanced  by  the  beneficial  effects  of  separation 
above  mentioned.  Undoubtedly  a  certain  amount  of  subdivision  by 
means  of  baffles  is  often  advantageous  where  the  water  enters  or  leaves 
at  a  single  point,  as  otherwise  there  is  certain  to  be  much  inequality  in 
the  velocities.  Where  baffles  or  a  series  of  reservoirs  are  used  the 
operation  of  each  division  should  be  arranged  according  to  the  same 
principles  as  apply  to  the  single  reservoir.  Inlets  near  the  bottom 
and  outlets  near  the  top  are  preferable,  but  baffles  are  quite  commonly 
arranged  merely  to  guide  the  water  in  a  circuitous  path  through  the 
basin  at  full  depth  at  all  points,  thus  making  in  effect  a  long  and 
narrow  but  tortuous  channel. 

Where  a  series  of  compartments  is  thus  used  the  first  one  may 
economically  be  operated  at  much  higher  velocities  than  the  following. 
Theoretically  the  maximum  efficiency  would  be  secured  when  the 
velocity  of  the  water  is  progressively  less  as  it  moves  forward  in  the 
series,  since  the  sediment  remaining  becomes  progressively  finer.  As  to 
the  number  of  such  basins  in  series,  it  will  seldom  be  economical  to  use 
more  than  two  or  three.  At  St.  Louis,  where  six  basins  were  available 
when  the  continuous  process  was  adopted,  the  results  obtained  at  the 


ARRANGEMENT  OF  PIPES. 


443 


successive  weir  outlets  is  represented   by  the  following  averages  for 
March,  1907:* 

SUSPENDED   SOLIDS,  PARTS   PER   MILLION. 
River.       Weir  i.       Weir  2.       Weir  3.       Weir  4-       Weir  5.       Weir  6. 

1444  14.2  12. I  8.35  7.1  5.8  5.46 

The  reduction  beyond  the  third  basin  is  very  small. 

481.  Arrangement  of  Pipes,  Intermittent  System.  —  In  this  system, 
since  the  water  may  enter  rapidly,  the  inlet  is  arranged  in  the  simplest 
way,  as  in  an  ordinary  reservoir.  The  position  of  the  outlet  is  of  more 
importance.  If  but  a  single  one  is  used,  it  will  need  to  be  at  the 
lowest  point  of  outflow,  and  so  will  not  draw  from  the  clearest  stratum 
except  near  the  end  of  the  operation.  The  difference  in  clearness  at 
different  depths  after  24  hours'  subsidence  or  more  is,  however,  not  very 
great.  At  St.  Louis,  observation  showed  that  there  was  very  little 
difference  in  clearness  from  top  to  bottom,  and  but  a  single  outlet  was 
there  provided.  Experiments  at  Cincinnati!  showed  that  the  upper 
6  inches  was  considerably  clearer  than  the  water  lower  down,  but  that 
below  this  there  was  little  change.  The  results  of  the  experiments  are 
given  in  Table  No.  67.  The  time  of  settlement  was  72  hours. 

TABLE    NO.  67. 
EXPERIMENTS  ON  SEDIMENTATION  AT  CINCINNATI. 


Depth  of  Sample, 

Suspended  Matter, 

Percentage 

Feet. 

Parts  per  Million. 

Removal. 

0.25 

137 

78.8 

3.00 

190 

7°-3 

8.00 

195 

69.5 

13.00 

197 

69.2 

23.00 

206 

67.8 

28.00 

2OO 

68.7 

30.00 

215 

66.4 

31.00 

200 

68.7 

32.00 

206 

67.8 

33-75 

641 

oo.o 

Unless  the  water  can  be  drawn  from  very  near  the  surface  little 
advantage  is  gained  in  ordinary  shallow  basins  by  constructing  an 
outlet  near  the  top.  With  a  depth  such  as  at  Cincinnati,  however, 


*  Eng.  Record,  1907,  LVI.  p.  98. 
t  Report  on  Purification,  p.  121. 


444  SEDIMENTATION  AND   COAGULATION. 

there  would  be  some  advantage  in  two  outlets  instead  of  one.  To 
enable  water  to  be  drawn  always  from  near  the  surface,  the  adjust- 
able outlet  pipe  described  in  Chapter  XXVII  is  used  to  advantage 
in  many  reservoirs,  and  among  these  the  new  settling-reservoirs  at 
Cincinnati. 

482.  Drain-pipes. — To   enable    the    sediment    to  be    removed,   the 
bottom  of  the  basin  should  be  made  slightly  sloping  (i  to  2  per  cent 
grade)  towards  a  central  drain  leading  to  an  outlet -gate  or  to  a  drain- 
pipe.    The  mud  is  removed  by  flushing  it  into  the  drain  by  means  of 
a   hose-stream,  supplied   from  a   high-pressure   main.     The  cleaning  is 
done  at   intervals  depending   entirely  upon   the   local    conditions,  and 
may  be  every  month  or  so,  or  only  at  intervals  of  years.     The  longer 
the  mud  is  allowed   to  remain  the  more  compact  it  becomes  and  the 
more  difficult  to  remove,  but   the  change  in  compactness  takes  place 
quite  slowly. 

483.  Clear-water  Well.  —  Where   the   basins   are   operated  on  the 
continuous-flow  system  and  the  water  passes  from  them  directly  to  the 
pumps,  it  is  necessary  to  interpolate  a  small  clear-water  or  pump  well 
to  avoid  the  necessity  of  too  frequent  adjustment  of  the  rate  of  supply 
to  the    basins.     It   is  not    necessary  that   the  operation   be  perfectly 
uniform,  for  the  loss  in  efficiency  due  to  a  more  rapid  motion  through 
the  basins  part  of  the  time  is  largely  compensated  by  a  reduced  rate  of 
flow  at  other  times. 

483 a.  Preparation  and  Control  of  Coagulant.  —  In  using  a  coagu- 
lant it  is  of  the  utmost  importance  that  the  introduction  of  the  proper 
amount  at  all  times  be  certain.  This  is  especially  true  where  a 
coagulant  is  depended  upon  in  rapid  nitration  of  sewage  polluted  water 
where  the  interruption  of  the  process  would  endanger  the  health  of  the 
community.  This  element  has  been  a  strong  argument  against  the  use 
of  the  rapid  filter  for  such  waters.  This  feature  of  operation  has, 
however,  been  so  well  perfected  in  the  more  recent  plants  that  the 
objection  has  lost  much  of  its  force. 

A  common  method  of  supplying  a  known  quantity  of  coagulant  is 
first  to  prepare  the  solution  of  known  strength  in  independent  mixing 
tanks,  a  duplicate  set  of  these  tanks  being  used.  Then  from  one  of 
these  tanks  the  prepared  solution  is  pumped  or  conveyed  to  a  smaller 
orifice  or  dosing  tank  in  which  the  liquid  is  maintained  at  a  constant 
level,  usually  by  applying  an  excess  and  permitting  the  surplus  to  over- 
flow over  a  weir  and  return  to  the  mixing  tank.  From  this  orifice  tank 
the  solution  is  fed  through  an  orifice  of  known  capacity.  The  head  on 
the  orifice  is  thus  constant  and  the  rate  of  flow  is  regulated  to  any 


PREPARATION  AND   CONTROL    OF  COAGULANT.  445 

desired  quantity  by  regulating  the  size  of  orifice  by  hand  wheel  with 
suitable  indicator.  The  liquid  should  be  permitted  to  pass  this  orifice 
into  free  air  and  not  directly  into  a  closed  pipe,  as  the  latter  arrange- 
ment would  give  rise  to  uncertainty  as  to  head.  Such  apparatus  must 
be  occasionally  checked  to  guard  against  the  effect  of  corrosion  or 
clogging  from  accretions  of  chemical.  Accurate  regulation  requires  a 
knowledge  of  the  rate  of  flow  of  the  water-supply  as  well  as  that  of  the 
coagulant.  This  is  obtained  from  the  pump  counters,  if  pumps  are 
used,  or  may  be  conveniently  got  by  the  use  of  venturi  meters.  While 
being  used  the  contents  of  a  mixing  tank  must  be  of  uniform  strength. 
This  is  accomplished  by  stirring  with  paddles,  or  by  agitation  with 
air,  or  by  other  mechanical  means.  Such  agitation  also  aids  greatly 
in  the  preparation  of  the  solution.  Lime  may  be  used  either  as  milk 
of  lime  or  lime  water,  the  latter  requiring  a  relatively  large  amount 
of  water  in  its  preparation,  but  giving  more  uniform  and  reliable 
results. 

In  large  plants  where  the  quantities  handled  are  large  the  prepara- 
tion of  the  chemical  may  be  more  economically  carried  out  by  the 
continuous  method,  no  storage  of  prepared  solutions  being  required. 
This  involves  accurate  and  convenient  means  for  measuring  out  and 
introducing  into  the  mixing  tanks  any  desired  quantity  of  chemical  and 
at  very  frequent  intervals.* 

The  amount  of  coagulant  needed  is  determined  by  frequent  analyses 
of  the  water  and  by  direct  observation  of  results  secured.  In  the  use 
of  alum  it  is  very  essential  that  there  be  sufficient  lime  present  in  the 
water  to  decompose  all  of  the  sulfate  of  alumina  used. 

In  the  construction  of  the  apparatus  for  the  preparation  of  the 
coagulant  great  care  should  be  exercised  to  secure  substantial  and 
durable  work.  Bronze  and  rubber  fittings  must  be  used  in  machinery 
for  handling  alum,  and  pipes  should  be  of  brass,  bronze  or  lead.  Tanks 
and  large  conduits  are  advantageously  made  of  reinforced  concrete. 

A  coagulant  is  introduced  into  the  water  in  various  ways.  A  com- 
mon and  satisfactory  method  is  to  introduce  the  solution  into  the  water 
in  a  conduit  or  channel  by  means  of  a  series  of  perforated  tubes  distrib- 
uted over  the  entire  section ;  or  by  such  perforated  tubes  placed  along 
a  weir  over  which  the  water  passes.  It  may  also  be  introduced  just 
previous  to  where  the  water  passes  through  pumps,  but  this  method  is 
not  desirable  where  lime  is  used,  as  this  tends  to  cause  accretions  on 
the  machinery. 

*  See  Proc.  Am.  Soc.  C  E.,  Sept.  1907,  for  description  of  the  large  plant  at  St. 
Louis. 


446 


SEDIMENTATION  AND   COAGULATION. 


EXAMPLES   OF  SETTLING-BASINS. 


447 


484.  Examples  of  Settling-basins.  —  The  St.  Louis  settling-basins  con- 
stitute the  largest  plant  of  its  kind  ever  built.  The  general  arrangement  of 
intake-pumps,  basins,  and  filling  and  drawing  conduits  is  shown  in  Fig.  118. 
The  basins  are  of  22,000,000  gallons  drawing  capacity  each.  They  are  built 
with  masonry  side  and  partition  walls,  and  linings  of  concrete,  on  about  18 
inches  of  puddle.  Through  the  center  runs  a  ditch  having  a  slope  of  i  per 
cent,  and  leading  to  a  24-inch  drain-pipe  at  the  easfr  end.  The  floor  also 
slopes  towards  this  ditch  from  both  sides.  Formerly  these  basins  were 
operated  on  the  fill-and-draw  system,  the  filling  being  done  through  a  masonry 
conduit  on  the  west  side  and  the  drawing  through  a  similar  conduit  on  the 
east.  They  are  now  operated  as  coagulating  basins  on  the  continuous  system, 
the  end  basins  being  used  alternately  as  supply  basins,  communication  from 
basin  to  basin  being  effected  by  means  of  long  weirs  in  the  division  walls. 

A  compact  design  for  a  settling-basin  is  that  for  the  city  of  St.  Joseph,  Mo., 
illustrated   in   Fig.   119,    Mr.   W}-nkoop    Kiersted,    Mem.   Am.    Soc.  C.   E., 


_  _"_../ 

tO' Delivery  Pipe  to  Reservoir:'  ~  Suction  Pipes  to  )          \  ?4%rce 
High  Scwc  Pumps.      \    Mom. 

THE  ENGINEERING  RECORD. 

FIG.  119. —  SETTLING-BASIN  AT  ST.  JOSEPH,  Mo. 

(From  Engineering  Record,  vol.  XL.) 

engineer.     The  following  description  is  from  an  article  by  Mr.  Kiersted  in 
the  Engineering  Record,  1889,  vol.  XL.  p.  506. 

"  The  water  delivered  by  the  low-service  pumps  enters  the  basin  No.  i  at 
the  points  A  and  B  either  when  all  three  basins  are  in  operation,  or  when 
basins  i  and  2  are  in  operation  and  No.  3  is  empty  for  cleaning;  at  point  C 
when  basins  i  and  3  are  in  operation,  and  at  D  when  No.  i  is  empty  for 
cleaning.  The  continuous  method  of  sedimentation  is  recommended;  conse- 
quently communication  between  the  basins  is  made  by  weirs. "  When  basin 
No.  2  is  being  cleaned,  water  enters  basin  No.  i  at  C  and  overflows  the  arch 
at  E  and  thence  passes  through  pipe  F  into  the  bottom  of  No.  3.  It  is  pro- 
posed to  introduce  a  coagulant  into  the  water  as  it  passes  the  weirs,  through 
a  line  of  small  pipe  provided  with  suitable  openings.  The  bottoms  of  the 
basins  slope  in  each  case  towards  a  central  gutter  from  which  the  sewer 
drain-pipes  lead. 


448 


SEDIMENTATION  AND   COAGULATION. 


At  Cincinnati  the  arrangement  of  basins  for  secondary  sedimentation 
with  coagulation  is  shown  in  Fig.  uga.  Usually  each  of  the  three  basins  is 
operated  independently,  the  water  passing  through  but  a  single  basin.  In  all 
cases  the  water  is  admitted  to  the  basin  through  numerous  openings  in  an 
inlet  conduit  placed  at  one  end  and  near  the  bottom.  It  is  taken  out  through 
a  similar  conduit  at  the  opposite  end  placed  near  the  top.*  The  small  basin 
No.  3  may  be  used  when  necessary  for  a  second  treatment  with  coagulant. 
The  period  of  sedimentation  may  be  varied  from  0.4  hour  to  4.7  Lours. 


Gcagns/cif/on  Bars/nNc  S 


/n/ef- 


FIG.  uga.  —  CINCINNATI  COAGULATION  BASINS. 

(From  Eng.  Record,  vol.  LV.) 

At  Pittsburg  three  basins  are  provided,  a  central  receiving  basin  of 
relatively  small  size  and  two  larger  basins  on  either  side.  The  water  enters 
the  receiving  basin  through  numerous  openings  in  a  large  conduit  in  the 
center  of  the  basin.  The  velocity  of  entrance  is  low  and  sedimentation  of  the 
coarser  particles  promptly  begins.  From  the  central  basin  the  partially 
settled  water  passes  to  the  larger  basins,  likewise  through  a  perforated  con- 

*  Eng.  Record^  1907,  LV.  p.  431. 


EXAMPLES  OF  SETTLING-BASINS.  449 

,/ 

duit  extending  entirely  across  the  end  of  each  basin.  Settled  water  is  drawn 
off  at  the  opposite  ends  from  a  series  of  openings  arranged  as  weirs  and 
leading  to  the  outlet  conduit*  See  also  Chapter  XXII  for  examples  of 
coagulating  basins  in  connection  with  rapid  filters. 

The  settling-basin  at  Albany,  N.  Y.,  used  in  connection  with  the  filter- 
plant,  possesses  several  features  worthy  of  notice.  (For  illustration  see  page 
467.)  The  capacity  is  14,600,000  gallons,  or  about  i^  days'  supply.  The 
operation  is  continuous,  water  being  admitted  through  eleven  inlets  along  one 
side  and  flowing  out  through  an  equal  number  of  overflow-pipes  on  the  oppo- 
site side.  The  inlet-pipes  rise  4  feet  above  the  water-line  and  are  perforated, 
this  causing  aeration  of  the  water  as  it  enters.  An  overflow  is  provided 
through  a  manhole  as  shown  on  the  plan  (Fig.  120).  A  waste  or  blow-off 
pipe  leads  from  a  sump  near  the  center,  towards  which  point  the  bottom 
slopes  from  all  directions.  As  the  Hudson  River  water  is  clear  during  a  large 
portion  of  the  year,  the  basin  can  be  readily  thrown  out  of  service  for 
cleaning.! 

LITERATURE. 

(See  also  references  of  Chap.  XIX.) 

1.  Seddon.     Clearing  Water  by  Settlement;    Observations   and   Theories. 

Jour.  Assn.  Eng.   Soc.,   1889,  vm.  p.  477. 

2.  Settling-basins  for  the   Low-service  Extension   of  the    St..  Louis,    Mo., 

Water-works.     Eng.  News,  1891,  xxv.  p.  380. 

3.  Gwinn.      The    Quincy,     111.,     Settling-reservoirs.      Eng.    Record,    1898, 

xxxvin.  p.  8. 

4.  Bacteria  Reduction  by  Storage  at  London.     Eng.  Record,  1898,  xxxvin. 

p.  230. 

5.  The  New  Settling  and  Aerating  Basins,  Fort  Smith,  Ark.     Eng.  News, 

1898,  XL.  p.  107. 

6.  Kiersted.      Sedimentation-basins  for  Water-works.     Eng.  Record,   1899, 

XL.  p.  506. 

7.  Kiersted.     Reinforcement  of  the  Walls  of  the  Kansas  City  Settling-basins 

and  the  Use  of  a  Coagulant  to  aid  Clarification.     Eng.  News,  1900, 
XLIII.  p.  3. 

8.  Sedimentation  Tanks  with  Numerous  Overflow  Weirs  ;    Denver  Union 

Water  Co.     Eng.  News,  1900,  XLIV.  p.  322. 

9.  Kiersted.     The  Utility  of  Subsiding  Basins.     Eng.  Record,   1902,  XLV. 

p.  468. 

10.  Hazen.     On  Sedimentation.     Trans.  Am.  Soc.  C.  E.,  1904,  LIII.  p.  45. 

11.  Patton.     Sulfate  of  Iron  as  a  Coagulant  in  Water  Sedimentation.     Eng. 

Record,  1906,  LIV.  p.  475  ;  Eng.  News,  1906,  LVI.  p.  363. 

12.  Elms.     Sulfate  of  Iron  and  Caustic  Lime  as  Coagulants  in  Water  Puri- 

fication.   Eng.   Record,  1906,  LIV.  p.   439  ;  Eng.  News,  1906,  LVI. 
P-  362. 

13.  The    Settling   Reservoirs  of  the    New   Cincinnati   Water-works.      Eng. 

Record,  1907,  LV.  p.  672. 

14.  Wall.     Water  Purification  at  St.  Lcula.  Mo.     Proc.  Am.  Soc.  C.  E.,  Sept. 

!907>  p.  758- 
See  also  references  10,  11,  14,  15,  19,  22,  27  of  Chapter  XXII. 

*  Eng.  Record,  1906,  LIV.  p.  622. 

t  For  full  description  see  Trans.  Am.  Soc.  C.  E.,  1900,  XLIII.  p.  256. 


CHAPTER   XXI. 
SLOW  SAND  FILTRATION. 

485.  Historical. — The  first  filter  of  which  we  have  any  record  was 
established  by  Mr.  James  Simpson  in  1829  for  the  Chelsea  Water 
Company  of  London.  The  chief  object  of  this  filter  was  to  remove 
turbidity,  and  in  this  it  was  a  success.  Its  value  in  improving  the 
water  from  a  hygienic  standpoint  was  also  appreciated,  although  the 
principles  underlying  its  action  were  not  understood  until  some  years 
later.  As  a  consequence  of  the  good  results  obtained  from  this  filter, 
'the  filtration  of  all  river-water  supplies  of  London  was  made  compul- 
sory in  1855*.  Similar  filter-plants  were  also  soon  established  at  several 
places  on  the  Continent. 

When  efficient  chemical  methods  of  water  analysis  were  devised 
about  1870  and  applied  to  the  subject  of  filtration,  it  was  found  that 
but  little  purification,  chemically,  was  effected  by  the  process.  The 
result  was  disappointing,  as  the  organic  matter  itself  was  at  that  time 
considered  to  be  a  chief  cause  of  disease.  After  the  establishment  of 
the  germ  theory  of  disease  and  the  application  of  modern  bacteriologi- 
cal methods  to  water  filtration  by  Prof.  P.  F.  Frankland  in  1885,  the 
subject  was  put  upon  an  entirely  new  and  substantial  basis ;  for  it  was 
found,  fortunately,  that  the  sand  filter,  although  showing  imperfect 
results  from  a  chemical  standpoint,  was  an  excellent  medium  for 
removing  bacteria.  It  is  thus  interesting  and  valuable  to  note  that  this 
process,  which  was  developed  empirically,  really  had  a  scientific  founda- 
tion. 

Within  the  last  fifteen  or  twenty  years  the  use  of  sand  filters  has 
become  almost  universal  abroad  wherever  surface-waters  are  used.  In 
Germany  it  is  compulsory.  It  is  estimated  that  at  least  30,000,000 
people  are  now  (1907)  supplied  with  filtered  water.  In  the  United  States 
it  is  only  very  recently  that  this  subject  has  received  the  attention  that 
it  merits.  In  view  of  these  facts  it  is  interesting  to  note  that  as  long 
ago  as  1869,  Mr.  J.  P.  Kirkwood  wrote  a  most  valuable  report  on 

450 


TYPES  OF  SAND  FILTERS. 


451 


filtration,  describing  therein  many  foreign  works  and  recommending 
the  adoption  of  the  system  in  St.  Louis.  The  recommendations, 
however,  were  not  adopted,  but  in  1872  a  filter  was  constructed  at 
Poughkeepsie,  N.  Y.,  under  Mr.  Kirkwood's  direction,  which  is  still  in 
operation.  A  similar  one  was  built  at  Hudson,  N.  Y.,  in  1874,  but  no 
others  until  recently.  An  important  step  in  the  development  was 
marked  by  the  completion  in  1899  of  a  fifteen-million-gallon  plant  at 
Albany,  N.  Y.,  the  largest  yet  constructed  at  that  time.  Since  this 
time  progress  has  been  rapid  and  some  very  large  plants  are  now  (1907) 
under  construction  or  have  recently  been  completed,  notably  for  the 
cities  of  Philadelphia,  Pittsburg,  Washington,  Cincinnati,  Louisville 
and  New  Orleans.  The  growth  in  the  use  of  filters  in  the  United  States 
is  shown  by  the  following  statistics  from  Hazen.* 

TABLE    SHOWING    USE    OF   FILTERS    IN   THE   UNITED   STATES. 


Total  Urban 

Population  Supplied  with  Filtered  Water. 

Percentage  of 

Population  in  the 

Urban  Popula- 

Year. 

United  States 

tion  supplied 

(Towns  above 
2,500). 

Slow 
Sand  Filters. 

Rapid  or 
Mechanical  Filters. 

Total. 

with  filtered 
Water. 

1870 

None. 

None. 

None. 

O 

1880 

13,300,000 

30,000 

30,000 

0.23 

1890 

21,400,000 

35,000 

275,000 

310,000 

1.45 

1900 

29,500,000 

360,000 

1,500,000 

1,860,000 

6.3 

1904 

32,700,000 

560,000 

2,600,000 

3,160,000 

9-7 

486.  Types  of  Sand  Filters.  —  Sand  filters  are  of  two  general  types, 
the  slow  filter  and  the  rapid  filter.  The  former  is  operated  at  a  rate  of 
from  2,000,000  to  6,000,000  gallons  per  acre  per  day,  while  the  latter 
is  generally  operated  at  a  rate  of  from  100,000,000  to  125,000,000  gal- 
lons per  acre  per  day.  These  very  great  differences  in  rate  of  filtration 
necessitate  important  differences  in  construction  and  methods  of  opera- 
tion in  order  to  secure  satisfactory  and  economical  results,  but  the  rate  of 
filtration  is  the  essential  point  of  difference  between  the  two  types. 

In  the  slow  sand  filter  the  sand-bed  is  constructed  in  large  water-tight 
reservoirs,  either  open  or  covered,  each  having  usually  an  area  of  from 
\  to  ij  acres.  On  the  bottom  of  the  reservoir  is  first  laid  a  system  of 
drains,  then  above  this  are  placed  successive  layers  of  broken  stone  and 
gravel  of  decreasing  size,  and  finally  the  bed  of  from  2  to  5  feet  of  sand 
which  forms  the  true  filter.  The  water  flows  by  gravity,  or  is  pumped, 

*  Trans.  Am.  Soc.  C.  E.  1905,  LIV.  D.  p.  145. 


452 


SLOW  SAND   FILTRATION. 


upon  the  filter,  passes  through  the  underdrains  to  a  collecting-well,  and 
thence  to  the  consumer.  As  the  water  filters  through  the  sand,  the 
friction  causes  some  loss  of  head,  which  gradually  increases  as  the  filter 
becomes  clogged  with  foreign  matter.  The  rate  of  filtration  is,  how- 
ever, maintained  nearly  uniform  by  suitable  regulating  devices  which 
vary  the  head  according  to  the  resistance.  When  the  working  head  has 
reached  a  certain  fixed  limit  of  a  few  feet,  the  water  is  shut  off,  the 
filter  drained,  and  the  surface  cleaned  by  removing  a  thin  layer  of 
clogged  sand.  The  operation  is  then  resumed.  Before  the  thickness 
of  the  sand  layer  becomes  too  greatly  reduced,  clean  sand  is  added 
sufficient  to  restore  the  filter  to  its  original  depth.  The  chief  fea- 
tures to  consider  in  this  form  of  filter  are  the  proper  construction  of 
sand-bed  and  drains,  the  rate  of  filtration  and  its  regulation,  the  loss  of 
head,  cleaning  of  beds,  washing  of  sand,  and  the  control  of  the  opera- 
tion by  bacteriological  tests. 

The  rapid  filter  differs  from  the  slow  filter  in  many  of  its  details. 
It  is  built  in  much  smaller  units,  and  the  drainage  system  and  operating 
devices  are  widely  different.  Furthermore,  in  its  operation  it  is  depend- 
ent upon  the  use  of  a  coagulant  for  efficient  results.  Further  discussion 
of  this  type  of  filter  is  given  in  the  next  chapter. 

THEORY  AND  EFFICIENCY  OF  FILTRATION. 

487.  General  Results  of  Filtration.  —  In  filtering  water  through  a 
sand  filter  the  main  improvement  to  be  noted  is  in  the  removal  of  the 
suspended  matter.     Even  the  color  of  a  peaty  water  may  be  somewhat 
lessened,  but  that  portion  of  the  color  due  to  matter  in  solution  is  not 
so  readily  removed  by  filtration.     With  respect  to  the  elimination  of 
bacteria  and  other  micro-organisms,  the  results  are  so  startling  that  it 
was  a  question  for  a  long  time  how  to  explain  them. 

488.  Bacterial  Results.  —  When  bacterial  cultures  are  made  from 
the  raw  water  and  from  the  effluent  of  a  properly  operated  sand  filter,  a 
very  great  reduction  in  the  number  of  bacteria  is  to  be  noted.     This  is 
well   illustrated  by  the  following  data  from  examinations  made  on  the 
Lawrence  City  filter,  which  uses  the  polluted  Merrimack  River  water. 

NO.   OF   BACTERIA  PER   C.C. 


1894- 

1895. 

1896. 

1897. 

1898. 

Raw  water 

10,41  7 

1  1,1  1  1 

7,108 

10,360 

4,8t;o 

Filtered  water              .            .... 

176 

121 

*          OI 

61 

46 

Efficiency  of  purification  (per  cent). 

98-3I 

98.91 

98.72 

99.41 

98.95 

THEORY  AND  EFFICIENCY  OF  FILTRATION. 


453 


Typical  bacterial  results  obtained  with  a  water  comparatively  low  in 
germ  content  are  the  following  from  the  operations  of  the  Washington 
filters  for  nine  months  from  October,  1905  to  June,  1906.  The  raw 
water  is  thoroughly  settled  in  large  reservoirs.* 

RESULTS    OF   FILTRATION   AT    WASHINGTON,    D.  C. 


Month 

Bacteria  ] 

3er  c.c. 

Month 

Bacteria 

per  c.c. 

Water  from 
Reservoir. 

Filtered 
Water. 

Water  from 
Reservoir. 

Filtered 
Water. 

1905. 

October.    .    .    . 
November.    .    . 
December      .    . 
1906. 

I98 
153 
3750 

78 
27 
60 

1906. 
February     .    . 
March      .    .    . 
April    .... 
May.    .    .    . 

562 
654 

399 
66 

16 
19 

22 
17 

January     .    .    . 

1520 

39 

June     .... 

224 

17 

489.  Chemical  Results.  —  Usually  the  amount  of  organic  matter  of 
an  unstable  or  objectionable  character  present  in  a  raw  water  is  not  so 
large  that  the  question  of  nitrification  of  organic  matter,  or  the  chemi- 
cal purification  of  the  water,  is  of  great  importance.  Ordinary  sand 
filtration  does,  however,  effect  a  very  considerable  purification  in  this 
respect,  especially  in  the  case  of  a  badly  polluted  water,  such  as  the 
Merrimack  water  at  Lawrence.  The  average  results  obtained  at  the 
Lawrence  filters  for  six  years  were  as  follows  (see  also  Art.  539). 


Raw  Water. 

Effluent. 

Per  cent 
Removed. 

Color                            

0.43 

O   38 

II    6 

Albuminoid  ammonia  

O.  IQQ 

O    OQ4 

«J2    8 

Oxygen  consumed  

4-  2 

2.8 

•?•? 

490.  Theory  of  Filtration. — When  working  under  favorable  condi- 
tions, a  sand  filter  will  remove  very  nearly  all  of  the  bacteria  originally 
present  in  the  water.     At  first  glance,  it  might  be  thought  that  this 
filtration  process  was  merely  a  mechanical  one,  a  straining  out  of  the 
suspended  particles  by  the  sand  layers. 

491.  Inadequacy  of  Mechanical  Explanations. — There  are  various 
reasons  why  such  an  explanation  is  not  wholly  satisfactory,  although 
undoubtedly  the  mechanical  theory  is  effective  in  part.     Particles  too 
large  to  pass  into  the  pores  of  the  filters  are  of  course  removed  by  sim- 
ple straining  action.     This  action  is,  however,  relatively  unimportant. 


*  Trans.  Am.  Soc.  C.  E.  1907,  LVI.  p.  358. 


454  SLOW  SAND  FILTRATION. 

The  chief  effect  produced  that  may  be  considered  mechanical  in  prin- 
ciple is,  doubtless,  the  action  of  the  sand  bed  as  numerous  minute 
sedimentation  chambers,  which,  owing  to  their  small  size  and  the  low 
velocity  of  flow,  are  quite  efficient  in  the  removal  of  the  finer  suspended 
particles  including  bacteria.  In  this  way  particles  much  smaller  than 
the  pore  spaces  in  the  sand  are  removed  to  a  very  considerable  extent 
by  purely  mechanical  means.  If,  however,  the  process  was  purely 
mechanical,  the  filtered  water  should  be  as  good  at  one  time  as  another, 
but  such  is  not  usually  the  case.  When  a  sand  filter  is  first  installed, 
the  filtrate  is  much  richer  in  germ  life  than  it  is  later.  As  it  increases  in 
age,  it  becomes  more  efficient,  showing  that  some  other  factor  than 
purely  mechanical  removal,  functions  in  the  process.  The  character  of 
the  applied  water  has  also  much  to  do  with  the  quality  of.  the  effluent 
independent  of  its  bacterial  content.  If  the  mechanical  theory  were 
correct,  a  variation  in  the  fineness  of  the  sand  would  in  a  measure 
affect  the  efficiency  of  the  process,  but,  within  the  limits  ordinarily 
employed,  the  difference  in  results  due  to  variation  in  size  of  sand  grain 
is  very  slight.  The  lack  of  relation  between  the  number  of  bacteria  in 
the  affluent  and  effluent  is  also  against  a  mechanical  explanation. 

492.  Inadequacy  of  Chemical  Explanations.  —  The  chemical  changes 
that  are  to  be  noted  in  filtration  are  of  such  a  nature  that  it  is  hardly 
conceivable  that  a  satisfactory  explanation  of  the  phenomena  of  filtra- 
tion will  rest  upon  a  chemical  basis.     Generally  there  is  some  oxidation 
of  the  organic  matter,  as  is  shown  by  the  reduction  in  "  oxygen  con- 
sumed."    Most  of  the  improvement,  however,  in  the  chemical  condi- 
tion of  a  water  is  occasioned  not  by  purely  chemical  changes,  but  is  due 
to  the  action  of  the  living  organisms  present  in  the  filter. 

493.  Biological  Explanation.  —  As  previously  noted,  a  filter  improves 
in  efficiency  as  it  grows  older  until  it  finally  reaches  a  point  where  the 
flow  of  water  through  the  same  is  so  small  as  to  necessitate  cleaning, 
a  process  technically  known  as  scraping.     But  even  after  cleaning,  the 
results  obtained  are  better  with  filters  long  established  than  with  new 
ones.     With  the  improvement  in  the  bacterial  content  of  the  effluent,  a 
marked  change  occurs  in  the  character  of  the  sand,  particularly  in  the 
upper  layers. 

Naturally  the  suspended  matter  in  the  water,  apparent  turbidity  as 
well  as  bacteria,  is  intercepted  for  the  most  part  at  the  surface  of  the 
filter.  Where  there  is  an  appreciable  amount  of  these  substances  held 
in  suspension  in  the  water,  a  layer  is  quickly  formed  on  the  surface  that 
quite  changes  the  nature  of  the  sand.  Generally  the  coating  is  slimy 
and  gelatinous,  and  to  it  has  been  ascribed  the  filtering  power  of  a  sand 


THEORY  AND   EFFICIENCY  OF  FILTRATION. 


455 


filter.  This  layer  also  forms,  although  more  slowly,  in  waters  that  are 
relatively  deficient  in  suspended  matter,  at  least  where  particles  are  not 
sufficiently  numerous  to  cause  turbidity.  When  critically  examined  it 
is  found  to  contain  inorganic  matter,  as  silt  of  all  kinds,  organic  sub- 
stances, as  bacteria,  algae,  diatoms,  and  amorphous  material. 

While  this  jelly-like  deposit  is  forming  at  the  surface  there  is  also 
an  appreciable  action  of  a  similar  nature  going  on  in  the  depth  of  the 
filter.  In  this  case  the  formation  of  this  substance  is  produced  by 
living  causes,  organic  instead  of  inorganic  matter,  therefore,  predomi- 
nating in  its  composition.  This  is  due  to  the  growth  of  the  bacteria 
derived  from  the  sand  and  water,  the  slimy  matter  being  formed  by 
the  cells  themselves  and  the  exudation  from  the  same.  This  organic 
matter  accumulates  more  readily  in  summer  than  in  winter,  because  of 
the  more  favorable  growth  conditions. 

While  a  casual  examination  of  the  sand  layers  will  show  in  a  general 
way  the  distribution  of  the  organic  matter,  a  bacterial  study  demon- 
strates the  presence  of  the  organisms  in  the  body  of  the  filter,  but  they 
are  accumulated  in  much  larger  numbers  at  or  near  the  surface,  as  is 
evident  from  the  following  data  gathered  from  the  results  of  examina- 
tions often  filters  at  Lawrence.* 

TABLE    NO.    68. 

EXAMINATION    OF   TEN    FILTERS    AT    LAWRENCE  AS    TO    ORGANIC   CONTENT  AND  BACTERIA 
AT    DIFFERENT    DEPTHS    OF    THE    SAND  LAYER. 


Depth. 
Inches. 

Organic  Nitrogen. 
Parts  per  100,000 
by  Weight. 

Bacteria. 
Per  Gram. 

o-i 

20 

6,600,000 

I 

9-5 

1,940,000 

3 

6.4 

72O,OOO 

6 

4-7 

3OO.OOO 

12 

4.0 

9O,OOO 

24 

2-3 

47,000 

36 

1.6 

35,000 

48 

1.2 

29,000 

60 

1.2 

26,000 

494.  Importance  of  Sediment  Layer. — The  accumulation  at  the  sur- 
face of  the  filter  has  led  to  the  view  generally  accepted  by  the  German 
school  that  this  surface  sediment  layer  (Schmutzdecke  of  the  Germans) 
is  the  chief  agent  in  effective  filtration.  From  the  experiments  con- 
ducted at  various  places  in  this  country  it  is  quite  evident  that  too 


*  Report  Mass.  Bd.  of  Health,  1894,  p.  635. 


456 


SLOW  SAND  FILTRATION. 


much  emphasis  has  been  put  upon  the  filtering  power  of  this  layer,*  as 
is  shown  from  the  following  facts: 

Waters  so  free  from,  suspended  matter  as  to  show  no  turbidity  form 
by  bacterial  growth,  in  a  brief  time,  an  organic  slimy  deposit  in  and 
on  the  sand,  by  the  aid  of  which  good  effluents  are  produced.  Waters 
containing  much  inorganic  sediment  may  not  develop  enough  organic 
slime  to  bind  the  mineral  matter  into  a  layer  and  so  hold  it  on  the 
surface.  In  such  a  case  the  inorganic  solids  are  forced  into  the  body 
of  the  filter,  to  the  detriment  of  the  efficiency  of  the  same.  Again, 
filters  having  a  well-developed  superficial  sediment  layer  may  have  the 
continuity  of  the  same  broken  if  the  surface  of  the  filter-sand  be 
exposed  to  the  air.  This  peeling  of  the  slimy  surface-coat  ought  to 
disturb  the  efficiency  of  the  filtrate  if  this  layer  was  the  sole  effective 
agent  in  filtration,  as  has  been  generally  claimed.  But  such  is  not  the 
case  as  shown  by  the  Lawrence  tests. 

Still  again,  the.  removal  of  the  upper  layer  'of  the  sand  that  has 
become  clogged  through  deposition  of  suspended  matter  from  the  water 
ought  to  invariably  impair  the  efficiency  of  the  filtration  until  a  new 
layer  is  produced.  As  a  matter  of  fact  such  results  do  not  necessarily 
follow,  although  it  should  be  said  that  this  is  the  most  critical  period 
in  the  condition  of  the  filter.  The  Massachusetts  experiments  often 
show  as  good  an  effluent  immediately  after  cleaning  as  before.  Under 
the  same  auspices  it  has  also  been  noted  that  filters  often  become  more 
effective  with  age  and  long  service.  This  has  been  shown  particularly 
with  medium  coarse  or  coarse  sands.  The  efficiency  increased  in  one 
case  (Filter  iSa)  as  follows:  t 


Year. 

Rate. 
Gallons. 

Bacterial  Efficiency. 
Per  cent. 

1893 

2,000,000 

96  75 

1894 

4,5OO,OOO 

98.97 

1895 

4,5OO,OOO 

99-57 

Notwithstanding  the  increase  in  rate  and  the  diminution  in  depth  of 
sand  from  5  to  3  feet  (due  to  scraping)  in  two  years,  the  character  of 
the  effluent  steadily  improved. 

*  Reinsch  (Cent.  /.  Bakt.,  1894,  xvi.  p.  881)  also  emphasizes  in  the  case  of  the 
Altona  filters  the  importance  of  the  thickness  of  the  sand  layer  in  comparison  with 
the  sediment  layer. 

f  Mass.  Bd.  Health,  1895,  p.  511. 


THEORY  AND    EFFICIENCY   OF  FILTRATION.  4$? 

These  facts  cannot  well  be  explained  on  the  theory  that  the  effec- 
tive agent  in  filtration  is  merely  the  surface  layer.  They  are  readily 
explainable,  however,  if  one  considers  that  the  bacterial  growth  in  the 
body  of  the  filter  exerts  a  strong  effect  on  the  filtration  process.  The 
value  of  the  denser  surface  layer  should  not,  however,  be  entirely 
neglected,  but  the  relative  merits  of  the  organic  slime  in  the  inner 
layers  of  the  filter  should  not  be  overlooked. 

To  recapitulate,  the  effective  agent  in  filtration  in  sand  filters  is  the 
organic  slime  in  the  filter-bed  and  the  accumulated  surface  sediment 
layer,  which  is  made  up  of  both  inorganic  and  organic  constituents. 
A  filter  is  therefore  something  more  than  a  mere  mechanical  strainer, 
inasmuch  as  its  efficiency  rests  largely  upon  biological  causes.  The 
sand  itself  acts  as  a  mechanical  support  for  these  gelatinous  films, 
holding  them  intact;  for  this  reason  a  certain  depth  of  sand  is  necessary 
to  steady  the  action  of  the  filter  and  prevent  disturbance  of  this  organic 
slime. 

495.  Bacteria  in  the  Effluent. — Where  a  slow  sand  filter  is   doing 
satisfactory  work,  the  number  of  bacteria  found  in  the  effluent  is  on  the 
average  small,  either  when  expressed  absolutely  or  compared  with  the 
number  originally  present  in  the  unfiltered  water.      A    good  deal  of 
variation,  however,  exists  even  in  the  same  supply  when  a  continuous 
study  is  made  for  considerable  periods  of  time.      The  following  data 
from  the  weekly  results  obtained  in  the  Belmont  filtration    works   of 
Philadelphia  during  August  and  September,  1903,  illustrate  this  point :  * 

Filter  No.  Bacteria  per  c.  c.  in  filtered  water. 

i 19  9  6  13  8  21  22  26  55 

2 37  13  10  12  8  33  21  170  17 

5 10  10  8  12  21  18  99  7 

6 14  27  ii  10  10  59  220  21  6 

496.  Origin  of  Bacteria  in  Effluent.  —  It   is  of  considerable  impor- 
tance to  determine  the  origin  of  the  bacteria  appearing  in  the  effluent, 
especially  as  this  figure  is  used  in  interpreting  results  of  efficiency  of 
filtration.      When  bacteriological  methods  were  first  introduced,  it  was 
assumed  that  the  difference  between  the  number  in  the  water  before 
and  after  filtration  represented  the  number  removed.     This  assumption 
is  now  known  to  be  false.      If  a  specific  micro-organism,  such  as  B.  pro- 
digiosus,  which  does  not  possess  the  quality  of  developing  in  the  body 
of  the  filter  and  under-drains,  is  applied  in  sterile  water  to  the  filter, 

*Jour.  Frank.  Inst.,  1904,  CLVII.  p.  193. 


SLOW  SAND   FILTRATION. 

it  is  possible  to  determine  with  much  greater  accuracy  the  exact  origin 
of  the  respective  bacteria  in  the  effluent.  More  recently*  the  colon 
organism,  B.  coli  communis,  has  been  utilized  in  this  work.  The 
value  of  this  organism  lies  in  the  fact  that  it  is  generally  a  regular 
accompaniment  of  polluted  water,  and  therefore  if  it  should  appear  in 
the  effluent  its  presence  is  indicative  of  danger  to  some  extent. 

The  relative  proportion  which  actually  pass  through  a  filter  and 
those  which  develop  in  the  under-drains  will  vary  at  different  seasons 
of  the  year  and  under  different  conditions  as  to  filtration.  During  the 
colder  months,  when  the  water  is  low,  the  number  developing  in  the 
filter  will  be  at  a  minimum.  Increased  rate  of  filtration  will  diminish 
the  number  per  c.c.  in  the  drains  by  more  rapid  flushing,  while  the 
higher  velocity  will  tend  to  force  a  slightly  larger  number  through  the 
filter.  Of  the  two  classes  of  bacteria  appearing  in  the  effluent,  those 
that  develop  in  the  drains  and  body  of  the  filter  are  the  least  important. 
They  are  generally  the  distinctive  water  organisms  that  naturally  grow 
in  such  a  habitat. 

If  the  sand  of  a  filter  is  sterilized  by  steam  or  by  the  addition  of  a 
chemical  disinfectant,  and  the  water  allowed  to  filter  through  the  same, 
it  has  been  observed  that  the  effluent  often  contains  more  bacteria  than 
the  unfiltered  water.  This  is  due  to  the  rapid  development  of  bacteria 
in  the  sterilized  sand,  there  being  enough  organisms  derived  from  the 
percolating  water  to  seed  the  filter.  In  the  "  cooked  "  filter  the  con- 
ditions seem  to  favor  very  rapid  growth.  The  high  number  in  the 
effluent  then  in  a  case  like  this  is  not  due  to  filtration  through  the  filter 
as  was  formerly  supposed. 

497.  Efficiency  of  Filtration. — Since  the  introduction  of  bacterio- 
logical methods  it  has  been  customary  to  consider  the  ratio  of  the 
difference  between  the  number  of  bacteria  in  the  raw  water  and  in  the 
effluent,  to  the  number  of  bacteria  in  the  raw  water,  as  an  index  of  the 
efficiency  of  operation,  and  this  number  is  frequently  referred  to  as  the 
bacterial  efficiency. t  Inasmuch  as  the  bacteria  in  the  effluent  includes 
those  organisms  of  post-filtration  origin  as  well  as  those  that  have  found 
their  way  through  the  filter,  this  bacterial  efficiency  evidently  does  not 
represent  accurately  the  number  of  bacteria  removed  from  the  water. 
To  determine  this  factor,  which  has  been  called  the  bacterial  purifica- 
tion>  it  is  necessary  to  add  some  special  form  to  the  applied  water,  as 
B.  prodigiosus  or  B.  coli  communis,  and  then  determine  its  frequency 
in  the  filtered  water.  The  hygienic  efficiency  is  the  percentage  removed 

*  Clark  &  Gage.     Science,  Mch.  23.  1900. 
\  Mass.  Bd.  of  Health,  1894,  p.  592. 


THEORY  AND   EFFICIENCY  OF  FILTRATION. 


459 


by  filtration  of  applied  bacteria  capable  of  producing  disease.  It  does 
not  necessarily  follow  because  one  organism  is  able  to  pass  through  a 
filter  that  all  others  will,  so  the  hygienic  efficiency  and  the  bacterial 
purification  may  not  correspond  closely.  These  relations  are  brought 
out  strikingly  in  the  tests  made  on  the  Lawrence  City  filter,*  which 
were  as  follows: 


Number  of  Cases 
of  Typhoid  in  City. 

Bacterial 
Efficiency. 
Per  cent. 

Percentage  of 
Cases  in  which 
B.  colt  was  found 
in  i  c.c.  of  Water. 

12 

O2   2 

72 

to 

y*»* 

c8  31 

ej. 

12 

Vw'.l* 

08.17 

62 

QQ    80 

8 

Under  ordinary  working  conditions,  the  germ  content  of  the 
effluent  should  be  reduced  to  the  lowest  possible  terms.  The  German 
standard  calls  for  an  effluent  with  not  to  exceed  100  bacteria  per  c.c. 
when  cultures  are  grown  in  gelatin  for  two  days,  but  as  a  matter  of  fact 
this  number  is  frequently  exceeded  even  in  good  working  filters, 
although  the  average  number  is  usually  below  this  limit.  Generally 
speaking,  the  efficiency  when  expressed  in  percentage  of  number 
present  in  raw  water  ranges  from  98  to  99  per  cent,  or  above.  In  the 
case  of  filters  using  quiescent  waters  as  sources  of  supply,  where 
the  number  of  bacteria  in  the  applied  water  is  low,  the  percentage  of 
bacterial  efficiency  is  of  course  reduced.  Where  the  source  of  supply  is 
from  running  streams,  the  bacterial  content  of  the  raw  water  is  much 
higher,  and  consequently  the  percentage  removed  is  much  greater. 
The  efficiency  of  filtration  is  also  much  affected  by  variation  in  working 
conditions,  as  by  a  fluctuation  in  rate  or  by  scraping  the  surface  of 
filter.  Formation  of  ice  on  uncovered  filters  is  also  detrimental. 

498.  Passage  of  Bacteria  Confirmed  by  Disease  Outbreaks.  —  The  pre- 
ceding experimentally  controlled  work  can  also  be  substantiated  by 
observations  made  on  the  practical  working  of  filters  in  relation  to 
disease  production.  Between  the  years  1886  and  1893  several  out- 
breaks of  typhoid  fever  occurred  in  Altona,  and  in  1891  a  marked 
epidemic  in  Berlin.  The  distribution  of  disease  in  these  two  cases  was 
such  that  it  was  evident  that  the  same  had  been  disseminated  by  the 
water-supply.  In  Altona  these  outbreaks  invariably  followed  similar 
epidemics  in  Hamburg.  In  Berlin  the  case  was  strikingly  emphasized, 

*  Clark  &  Gage.     Science,  Mch.  23,  1900. 


460 


SLOW  SAND   FILTRATION. 


because  the  outbreak  was  confined  to  the  region  supplied  by  the 
Stralau  (open)  filters.  At  that  time  no  search  was  made  for  the 
typhoid  germ,  but  later,  in  1894,  Losener  *  found  the  typhoid  organism 
in  the  tap-water  in  this  district,  a  discovery  that  was  confirmed  by 
Eisner. f  During  the  cholera  scourge  in  Germany  in  1892-3  the 
cholera  organism  appeared  in  the  filtered  water  of  at  least  four  cities.  J 
It  should,  however,  be  noted  that  in  these  cases  the  filters  were  not  in 
proper  working  conditions,  on  account  of  the  presence  of  ice.  Still 
again,  at  Rotterdam  in  1904,  typhoid  fever  was  transmitted  through 
the  agency  of  imperfectly  filtered  water  due  to  the  effect  of  winter 
weather  and  relatively  coarse  filters.  § 

Evidence  such  as  the  above  indicates  that  it  is  possible  for  even 
disease  bacteria  to  find  their  way  through  filters  that  are  under  unfavor- 
able working  conditions.  Under  normal  operating  conditions,  the 
passage  of  disease-producing  bacteria  is  very  rare. 

499.  Death-rates  as  Measures  of  Efficiency.  —  While  the  common 
method  of  expressing  the  efficiency  of  any  filter  is  to  measure  it  by  the 
bacteria  appearing  in  the  effluent,  either  expressed  absolutely  or  in 
terms  of  percentage  apparently  removed,  still,  after  all,  the  effect  on  the 
death-rate  or  the  case-rate  of  water-borne  diseases  is  the  crucial  test 
of  efficiency.  Where  statistics  are  comparable,  they  invariably  show 
a  diminution  in  death-rate  that  is  sometimes  so  marked  as  to  be 
astonishing.  The  following  table  from  Hazen  ||  exhibits  clearly  the 
effect  of  filtration  upon  the  typhoid  death-rate. 

TABLE   SHOWING    EFFECT   OF   THE   ADOPTION   OF   FILTRATION   UPON   THE  TYPHOID 

DEATH-KATE. 


Date  of 

Typhoid 

Death  Rate  per 

100,000. 

Place. 

Change. 

Five  Years 
before  Change. 

Five  Years 
after  Change. 

Percentage  of 
Reduction. 

l88< 

76 

IO 

87 

Hamburg   Germany 

A<J<JD 
IoQ2—  Q3 

4.7 

7 

85 

Lawrence   Miass                  .... 

1803 

121 

26 

70 

Albany,  N.  Y  

l899 

104 

28* 

73 

*  Four  years. 

Since  the  introduction  of  sand  filtration   into   Lawrence,  Mass.,  a 
city    that   formerly    used   the   polluted    Merrimack    River   water,   the 

*  Arbeit,  a.  d.  k.  Gesundheitsamte,  xi.  p.  240. 
t  Zeit.  f.  Hyg.,  xxi.  p.  30. 
t  Frankel,  C.    Hyg.  Rund.,  1896,  vi.  p.  3. 
§  Trans.  Am.  Soc.  C.  E.,  1905,  LIV.  D.,  p.  164. 
||  Trans.  Am.  Soc.  C.  E.,  1905,  LIV.  D.,  p.  151. 


RATE    OF  FILTRATION'.  461 

typhoid  rates  have  been  reduced  nearly  80  per  cent.  In  Hamburg  the 
death-rate  from  typhoid  was  diminished  by  the  installation  of  the  filter 
over  70  per  cent.  The  most  striking  instance  on  record  is  the  classic 
example  of  the  protection  afforded  to  the  city  of  Altona  in  the  summer 
of  1892,  while  its  sister  city,  Hamburg,  was  striken  with  cholera 
(216).  Numerous  European  cities  that  use  this  system  are  thus  able 
to  utilize  surface-waters  of  doubtful  purity,  and  by  treating  them  in 
this  way  to  insure  a  safe  supply. 

CONSTRUCTION   AND   OPERATION. 

500.  Rate  of  Filtration. — In  the  design  of  a  filter-plant  the  first 
question  to  be  settled  is  the  rate  of  filtration  which  shall  be  adopted. 
The  higher  the  rate  the  less  the  area  required  and  hence  the  less  will 
be  the  first  cost ;  but  the  cost  of  operation  is  not  greatly  affected  by  the 
rate,  so  that  the  economy  of  high  rates  is  not  as  great  as  it  might 
appear  at  first  sight. 

Rates  of  filtration  are  in  this  country  usually  stated  in  terms  of 
gallons  per  acre  per  day  or  per  hour,  and  on  the  Continent  in  meters 
depth  of  water  per  day  or  per  hour.* 

501.  Rates  Used  in  European  Practice. — The  experience  of  Euro- 
pean works  has  resulted  in  the  adoption  of  a  rate,  for  most  places,  of 
between  2  and  3  million  gallons  per  acre  per  day.     This  is  materially 
less  than  the  rate  of  3.9  millions  mentioned  by  Kirkwood  as  being  the 
average  in  1866,  and  denotes  a  marked  change  in  practice  since  that 
time. 

The  Hamburg  works,  completed  in  1893,  were  designed  on  a  basis 
of  1.6  millions.  At  Berlin  the  standard  rate  is  about  2.6  millions. 
At  London  the  average  rate  of  all  filters  is  about  1.8  million  gallons 
per  acre  per  day,  but  some  companies  use  as  high  as  2.5  millions. 
Rates  considerably  higher  than  these  are  used  in  a  few  places,  notably 
at  Zurich,  where  a  rate  of  nearly  8  millions  is  used  with  satisfactory 
results,  but  here  the  unfiltered  water  is  very  clear  and  contains  but  a 
few  hundred  bacteria  per  c.c. 

As  a  general  statement  100  mm.  per  hour  (equivalent  to  2.57 
million  gallons  per  acre  per  day)  is  considered  by  German  authorities 
as  a  standard  maximum  rate.  English  engineers  favor  a  slightly 
greater  rate  of  8  to  12  feet  per  day,  or  2.6  to  3.9  million  gallons  per 
acre. 


*  One  meter  per  day  is  equal  to   1.07  million   gallons  per  acre  per  day  ;  one  foot 
per  day  equals  0.326  million  gallons  per  acre  per  day. 


462  SLOW  SAND   FILTRATION1. 

502.  Effect  of  Rate  on  Efficiency. — The  long  experience  of  European 
works,  resulting  in  the  adoption  of  the  rates  given  above,  is  very 
strong  evidence  that  higher  rates  are  undesirable.  The  decreased 
efficiency  with  increased  rate  has  been  directly  shown  in  important  ex- 
perimental studies  by  Pief  ke  *  at  Berlin.  From  these  trials  he  recom- 
mended as  low.  as  1.28  million  gallons  per  acre  daily  as  a  safe  maximum 
rate,  but  more  recently  he  has  used  as  high  as  2.57  million  gallons. 

It  is  undoubtedly  true  that  high  rates  of  filtration  will  give  less 
efficiency  than  low  rates  when  the  difference  is  very  great,  but  much 
evidence  is  available  which  indicates  that,  under  certain  conditions,  no 
perceptible  decrease  in  efficiency  will  result  from  a  considerable  increase 
in  rate  beyond  the  standard  rates  mentioned  above.  Experiments  by 
Kiimmel  at  Altona  on  Elbe  water,  with  rates  of  4,  8,  and  16  feet  per 
day  (1.3,  2.6,  and  5.2  million  gallons  per  acre),  showed  equally  good 
results. t  At  Zurich,  rates  of  from  4.4  to  21.5  million  gallons  per  acre 
per  day  likewise  gave  equally  good  results.  The  latter  experiments 
are  not,  however,  especially  significant  for  normal  conditions  on 
account  of  the  extremely  clear  water  and  very  low  germ  content.  J 

The  most  important  experiments  in  this  direction  are  those  which 
have  been  carried  out  by  the  Massachusetts  Board  of  Health  at 
Lawrence,  Mass. ,  on  the  Merrimack  River  water.  This  water  is  not 
often  very  turbid,  but  is  badly  polluted  by  sewage.  It  contains  on  the 
average  about  0.2  parts  per  million  of  albuminoid  ammonia.  In  1892 
the  results  obtained  on  filters,  the  majority  of  which  had  been  in  opera- 
tion but  six  or  eight  months,  indicated  that  the  efficiency  §  decreased 
slightly  with  increase  in  rate,  even  for  rates  as  low  as  o.  5  to  3  million 
gallons  per  acre  daily.  In  1893,  with  older  filters,  the  influence  of  rate 
was  not  so  apparent,  but  high  rates  were  not  as  yet  used.  In  1894, 
rates  of  5  to  10  million  gallons  and  over  were  used  with  several  of  the 
filters,  with  satisfactory  results  "from  those  filters  which  had  been  in 
operation  for  a  considerable  period."  The  bacterial  efficiency  in  these 
cases  was  fully  99  per  cent.  With  such  high  rates,  however,  the  effect 
of  scraping  was  more  marked  than  with  low  rates.  Regarding  rates  in 
practice,  the  following  statement  is  made:  ||  "Experience  during  the 
past  ten  years  with  ten  different  filters  which  have  been  in  operation  at 
rates  of  5  million  gallons  or  more  per  acre  daily  leads  us  to  the  con- 

*  Jour.  f.  Gasbel.  u.   Wasservers.,  1891,  pp.  208,  228. 

f  Trans.  Am.  Soc.  C.  E.,  1893,  xxx.  p.  333. 

i  Proc.  Inst.  C.  E.,  CXL.  p.  280. 

§  Determined  by  the  percentage  of  B.  prodigiosus  that  passed  the  filters. 

|  Mass.  Bd.  Health,  1894,  p.  606. 


RATE   OF  FILTRATION.  463 

elusion  that,  with  conditions  substantially  equivalent  to  those  at 
Lawrence,  the  above-mentioned  rate  may  be  safely  adopted  in  practice 
and  yield  an  effluent  of  satisfactory  quality  after  the  first  or  second 
month  of  operation."  These  conclusions  are  further  substantiated  in 
the  report  for  1895,  entirely  satisfactory  results  having  been  obtained 
with  rates  of  5  to  7  million  gallons. 

503,  Rate  to  be  Adopted.  —  In  view  of  the  results  obtained  above 
and  the  statements  of  the  Board  based  on  many  years  of  experimenta- 
tion,  it    would   appear  that  rates   somewhat  higher  than   those  used 
abroad  could  be  adopted  with  safety.     In  the  Albany  plant  Mr.  Hazen 
assumed  a  rate  of  3  million  gallons,  and  in  most  of  the  important  plants 
constructed  since,   a  rate  of  about   3  million  has  been  adopted  as  the 
standard.     Considerably  higher  rates  have  been  used  in  some  cases  for 
the  filtration  of  relatively  clear  waters.     Where  a  preliminary  treatment 
is  employed,   of   greater  efficiency   than  ordinary  sedimentation,  such 
as  the  use  of  a  coagulant  with  sedimentation,  rapid  mechanical  filters, 
or    "scrubbers,"  the  rate  of    filtration  may    be    materially   increased, 
a  rate  of  6  to  8   million  gallons  being  then   quite   practicable.*  (See 
Art.  534.) 

A  conservative  course  should  unquestionably  be  followed  in  using 
higher  rates  than  those  established  by  past  experience,  and  probably 
3  or  4  million  gallons  is  as  high  as  it  would  in  general  be  advisable 
to  go  in  the  design  of  a  new  plant.  If  subsequent  operation  shows 
that  a  higher  rate  can  be  adopted  with  efficiency  and  economy,  the 
fact  can  be  taken  advantage  of  as  the  demand  for  water  increases. 
Local  conditions  are  apt  to  vary  widely  so  that  any  general  rule 
must  be  applied^  with  caution.  Each  case  demands  independent  con- 
sideration in  order  that  the  best  and  most  economical  solution  may 
be  arrived  at. 

504.  Uniform  Rate  Desirable.  —  Sudden  changes  of  rate  are  apt  to 
produce  disturbances  in  the   filter  and  to  give  a  reduced  efficiency. 
The   Lawrence  experiments   on  this  point  show  that  for  a  moderate 
increase  in  rate  of  10  or  20  per  cent  the  effect  is  inappreciable,  but 
that  a  large  reduction  in  efficiency  is  caused  by  an  increase  in  rate  of 
50  per  cent.     Marked  reductions  in  rate  followed  by  a  return  to  the 
normal  had  little  effect.     It  was  also  found  that  filters  most  sensitive 
to  such  changes  were  those  of  shallow  depth,  those  of  coarse  sand,  and 
those   that    had   been    but   a    short    time    in    operation.     In   practice, 
absolute  uniformity  of  operation  is  unnecessary,  but  sudden  changes  in 
rate  should  be  avoided,  and  especially  any  large  increase  above  the 
normal. 

*  For  additional  data  see  references  42  and  43  at  end  of  chapter. 


464  SLOW  SAND   FILTRATION. 

505.  Capacity. — The  standard    rate  having  been    determined,  the 
required  net  working  capacity  will  be  equal  to  the  maximum  rate  of 
delivery  divided  by  the  assumed  rate  of  filtration.     To  economize  area 
and  to  avoid  rapid  changes  in  rate,  a  clear-water  reservoir  should  be 
provided.     The  best  size  for  this  will  depend  on  local  conditions,  but 
it  will  usually  be  desirable  to  have  it  of  sufficient  capacity  to  equalize 
the  demand  throughout  the  day.      It  will  then  be  necessary  to  vary  the 
rate  of  filtration  only  to  accord  with  the  daily  variations  in  consumption 
(see  Art.  527).      In  Chapter  II  it  was  shown  that  the  maximum  daily 
rate  of  consumption  is  likely  to  be  about  175  per  cent  of  the  average, 
and  with  a  clear-water  reservoir  of  the  capacity  mentioned  above  the 
filters  must  be  designed  to  deliver  at  this  maximum  daily  rate.      If  the 
reservoir  has  a  less  capacity,  then  the  maximum  rate  of  delivery  of  the 
filters   will   be   correspondingly  increased.      Occasional   high  rates   of 
consumption  and  extraordinary  demands  may  be  provided  for  by  the 
use  of  a  rate  of  filtration  somewhat  higher  than  the  standard  adopted. 

In  addition  to  the  area  as  above  found,  a  reserve  area  for  cleaning 
must  be  provided.  For  small  works  this  will  be  one  bed ;  for  works 
containing  several  beds  it  will  be  necessary  to  allow  one  bed  for  each 
5  to  10  beds,  depending  on  the  frequency  of  scraping  and  the  time 
required  for  putting  a  filter  into  operation  after  cleaning. 

506.  Number  and  Size  of  Beds.— The  proper  size  of  beds  is  chiefly  a 
question  of  economical  construction.      The  larger  the  beds  the  less  the 
cost  per  acre,  but  the  greater  will  be  the  area  out  of  service  in  the  one 
or  more  reserve  beds.    Ordinarily  the  size  for  a  considerable  number  of 
beds  is  from   I  to  1.5  acres  for  open  beds,  and  from  .4  to  .8  acres  for 
covered  beds.      For  small  total  areas  of  .5  to   I  acre  three  beds  would 
ordinarily    be    used,    and    for    still    smaller    areas    two    beds.        The 
economical  number  can  in  any  case  be    determined    by  comparative 
estimates,  but  some   assistance   may  be  had  by  the   following  mathe- 
matical analysis. 

The  cost  of  a  filter  may  roughly  be  estimated  as  made  up  of  two 
items:  (i)  a  portion  proportional  to  the  area,  which  would  include  cost 
of  bottom,  filling,  small  drains,  cover,  and  the  end  walls,  we  will  say 
(basins  assumed  rectangular  and  placed  side  by  side);  and  (2)  a  portion 
nearly  independent  of  the  size,  such  as  cost  of  piping,  valves,  valve- 
chamber,  division  walls,  etc.  Let  c  =  amount  of  the  first  portion  per 
acre,  and  C  =  the  latter  portion  per  filter.  If  q  =  area  of  one  filter, 
n  =  number  of  filters,  and  A  ==  total  net  area  required,  then  if  one 
filter  is  to  be  held  in  reserve, 


NUMBER  AND   SIZE   OP  BEDS. 


465 


466  SLOW  SAND  FIL  TRA  TION. 

The  total  cost  is 


(2) 


CA 

—   +C+cA+cg,     ........     (3) 

9 

We  then  have  =  -  — +  C, 

dq  q2 

whence  for  a  minimum  cost 

(4) 

/7T 

that  is,  the  economical   area   is    proportional    to   \/ A    and   to    y  —  - 

*    c 

The  larger  the  value  of  c  the  smaller  is  q,  and  hence  for  covered  beds 

£ 

^  will  be  smaller  than  for  open  beds.     The  values  of  —  will  hardly  be 

larger  than  1  or  less  than  -jL,  giving  a  value  of  ^  =  -J-  v/^4  to  J  \/A 
Thus  when  ^4  =  I  acre,  the  capacity  would  be  ^  to  i  acre,  giving  3  or 
4  beds ;  for  A  =  4  acres,  ^  =  l  to  f ,  giving  6  to  8  beds  ;  and  for 
A  =  9  acres,  ^  =  f  to  I  acre,  giving  9  to  12  beds,  etc.  When  the 
number  becomes  so  large  as  to  require  two  beds  to  be  held  in  reserve 
the  size  will  no  longer  increase  with  the  area.  Sizes  considerably 
larger  than  I  acre  have  been  used,  such  as  1.9  acres  at  Hamburg,  but 
they  will  hardly  be  economical.  Such  large  beds  are  also  undesirable 
on  account  of  the  increased  difficulty  of  securing  uniform  operation. 

507.  General  Construction.  —  Filter-beds  are  usually  rectangular  in 
form  and  arranged  side  by  side  in  one  or  two  rows  according  to  the 
number.  The  shape  of  the  area  available  often  determines  this  point, 
but  otherwise  a  convenient  arrangement  is  to  place  them  in  two  rows 
with  a  space  between  for  sand-washing,  etc.,  and  to  have  valve-cham- 
bers facing  this  central  passage-way,  as  illustrated  by  the  Albany  plant 
(Fig.  120).  A  single  row  would  be  more  economical  of  masonry,  but 
would  require  more  piping. 

A  large  number  of  basins  may  be  divided  into  groups  and  arranged 
in  the  above  manner. 

The  economical  proportions  for  rectangular  beds  arranged  side  by 
side  is  approximately  given  by  the  formula  derived  in  Art.  479  for 


GENERAL  CONSTRUCTION. 


467 


settling-basins.     It  is  -  =  n  +  *  ,  where  b  =  width,  a  =  length,  and 
n  =  number  of  beds  in  a  row.     This  assumes  the  cost  per  lineal  foot  of 


fm 


Wliliti? 

Ira  Ml 

iia 


PS 


interior   and    exterior    walls    equal,  which    is    approximately  true.      A 
larger    cost    of    interior    walls  will  tend    to    increase  b  and  vice  versa. 


^468  SLOW  SAND  FILTRATION. 

The  cost  of  the  large  central  drain  running  lengthwise  of  the  bed  will 
also  tend  to  increase  b,  while  the  expense  of  exterior  piping  will  tend  to 
reduce  it. 

In  general  construction  a  filter-basin  is  built  in  a  way  similar  to 
small  distributing-reservoirs.  (See  Chapter  XXVII.)  Earth  embank- 
ments for  the  sides  are  cheaper  than  masonry  walls,  but  require  more 
ground.  If  the  filters  are  covered,  masonry  walls  are  usually  employed. 
Particular  care  must  be  taken  to  render  the  basin  water-tight,  both  on 


FIG.  122.  —  INTERIOR  VIEW;  WASHINGTON  FILTERS. 

(From  Trans.  Am.  Soc.  C.  E.,  vol.  LVII.) 

the  bottom  and  at  the  sides.  Cracks  in  division  walls  are  likely  to 
admit  unfiltered  water  to  the  under-drains  and  should  be  especially 
guarded  against. 

Concrete,  well  reinforced,  is  a  very  satisfactory  material  for  filter 
construction,  especially  with  respect  to  the  walls.  If  any  cracks  occur 
they  are  likely  to  be  very  minute.  In  the  construction  of  water-tight 
bottoms  good  results  have  been  secured  by  placing  concrete  in  sections 
in  two  layers,  so  arranged  that  the  sections  in  the  different  layers  will 
thoroughly  break  joints.  Covers  for  filters  are  constructed  in  the  same 
general  manner  as  described  in  Chapter  XXVII.  Reinforced  or  plain 
concrete  vaulting  is  usually  employed,  although  wood  has  been  used ; 
but  the  latter  does  not  afford  as  good  a  protection  from  freezing  or 
from  summer  heat.  Admission  for  workmen  is  provided  by  a  gangway 
leading  from  an  opening  at  a  point  where  the  vaulting  is  raised ;  or  the 


NECESSITY  FOR  COVERING  FILTERS. 


469 


entire  cover  may  be  made  of  the  necessary  height  to  give  ready  access 
at  any  point.  This  method  of  construction  offers  opportunity  for  light- 
ing and  ventilation  by  means  of  windows  in  the  outside  walls.  Walls 
and  piers  should  be  built  with  small  offsets  near  the  bottom  in  order  to 
insure  good  nitration  at  that  point.  The  covered  filter  at  Washington 
is  illustrated  in  Fig.  122.  Groined  arches  of  concrete  were  there  used. 
Fig.  123  shows  a  section  through  the  gangway  of  a  filter  and  also  the 


FIG.   123.  —  GENERAL  CONSTRUCTION  OF  A  COVERED  FILTER. 

(From  Report  on  the  Water-supply  of  Philadelphia,  1899.) 

general  method  of  construction.  In  some  of  the  most  recent  plants 
sand-run  tracks  are  dispensed  with,  the  sand  being  moved  through 
pipes. 

508.  Necessity  for  Covering  Filters.  —  Since  the  cost  of  covers 
amounts  to  about  one-third  of  the  total  cost  of  filters,  the  question  of 
open  versus  closed  filters  Li  a  very  important  one.  The  principal 
reason  for  covering  filters  io  to  avoid  the  difficulties  connected  with  the 
operation  of  open  filters  in  winter.  To  clean  filters  when  covered  with 
ice  is  a  troublesome  and  expensive  operation,  while  if  the  filters  are 
drained  for  cleaning,  trouble  arises  from  the  freezing  of  the  sand. 
Winter  operation  is  thus  likely  to  show  a  decreased  effective  area  and  a 
lowered  efficiency. 

At  Berlin  all  beds  are  now  covered.  At  Hamburg  open  filters  are 
used.  Ice  forms  there,  however,  to  a  thickness  of  10  or  12  inches  and 
causes  considerable  trouble  in  cleaning.  In  England  filters  are  not 


470  SLOW  SAND  FILTRATION. 

covered  and  little  trouble  is  experienced,  but  the  winters  are  quite 
mild,  the  mean  January  temperature  at  London  being  about  38°.  At 
Poughkeepsie,  N0  Y0,  and  at  Lawrence,  Mass.,  where  original  filters 
were  built  open,  it  was  found  that  a  large  expense  was  involved  in  the 
removal  of  ice.  The  Poughkeepsie  filters  have  since  been  covered,  and 
covers  have  been  used  in  additional  new  filters  at  Lawrence0  In  gen= 
eral  the  increased  convenience  and  regularity  resulting  from  the  use  of 
covers  tends  to  encourage  their  use  even  when  not  necessary  for  good 
efficiency. 

Mr.  Hazen  *  has  proposed  as  a  general  rule  that  covers  should  be 
used  where  the  average  January  temperature  is  below  32°.  This 
includes  the  area  north  of  a  line  passing  through  St.  Louis,  Cincinnati, 
Pittsburg,  and  Philadelphia.  In  the  large  plants  at  Pittsburg,  Wash- 
ington and  Philadelphia,  constructed  since  1900,  it  has,  however,  been 
found  desirable  to  use  covers0  On  the  other  hand,  open  filters  have 
been  built  at  Providence  and  Denver.  Whether  covers  should  be  used 
depends  upon  the  extent  to  which  ice  will  form,  the  frequency  of  the 
occurrence  of  thaws  which  will  enable  a  filter  to  be  properly  cleaned, 
and  the  length  of  time  between  cleanings  as  determined  by  the  charac- 
ter of  the  water. 

Another  very  considerable  advantage  of  covered  filters  in  some 
places  is  in  the  prevention  of  the  growth  of  algae,  and  thereby  reducing 
the  frequency  of  cleaning.  At  Zurich  both  open  and  closed  filters 
were  for  a  time  in  use.  The  number  of  days  between  scrapings  was 
on  the  average,  for  1891  and  1892,  as  follows  :f 

1891.       1892. 

Covered  filters 37  36 

Open  filters 28  23 

At  Poughkeepsie  much  trouble  was  also  experienced  from  the  growth  of 
algae  in  the  open  filters  there  used. 

509°  Effect  of  Cold  Weather  on  Efficiency  of  Filtration.  —  The 
reduced  efficiency  of  open  filters  in  winter  is  shown  by  the  results  of 
bacteriological  analyses,  and  is  further  substantiated  by  a  considerable 
number  of  disease  epidemics  that  have  broken  out  in  the  winter  in 
cities  supplied  with  filtered  water.  Freezing  weather  is  especially  apt 
to  have  a  detrimental  effect  in  connection  with  the  cleaning  of  the 
filter.  (See  Art.  531.) 

In  1889  the  effluent  of  the  Stralau  (uncovered)  filters  in  Berlin 
contained  on  the  average  less  than  100  bacteria  per  c.c.,  but  in  March 

*  Filtration  of  Public  Water-supplies,  p.  12. 
t  Report  Zurich  Water-works,  1892,  pc  27. 


THE  FILTERING  SAND.  471 

that  year,  at  a  time  when  the  filter  operations  were  interfered  with 
through  the  action  of  cold  weather,  the  number  rose  to  3  or  4  thousand. 
Coincident  with  this  change  occurred  a  typhoid  epidemic,  and  also 
one  of  dysentery,  that  were  limited  to  the  Stralau  district,  while  that 
portion  of  the  city  supplied  from  the  Tegel  filters  remained  free  from 
both  diseases.  The  history  of  the  open  filters  at  Altona  is  also  similar. 
Outbreaks  of  typhoid  have  occurred  explosively  at  Altona  in  the  win- 
ters of  1886,  1887,  1888,  1891,  and  1892,  and  Reincke  has  traced  these 
to  the  imperfect  operation  of  the  filters  during  cold  weather.  It  is 
significant  that  in  almost  every  case  these  outbreaks  were  preceded  by 
similar  epidemics  in  Hamburg,  and  furthermore  that  they  only  occurred 
in  Altona  during  the  winter,  when  the  action  of  the  filters  was  im- 
paired by  frost.  In  the  typhoid  outbreak  that  occurred  in  the  early 
part  of  1891,  Wallichs  *  had  noted  a  sudden  increase  from  a  normal  of 
less  than  100  bacteria  per  c.c.  to  2615.  The  small  winter  outbreak  of 
cholera  that  occurred  in  Altona  in  1893  Koch  was  able  to  trace  to  the 
imperfect  operation  of  a  single  filter. 

510.  The  Filtering  Sand.  —  In  selecting  a  sand  for  filtering  purposes 
the  important  properties  are  its  size  and  uniformity  of  grain,  the  pres- 
ence or  absence  of  fine  material  and  organic  matter,  and  its  chemical 
composition. 

511.  Mechanical  Analysis. — The  particles  of  any  given  sand  vary 
much  in  size,  but  as  regards  the  size  of  the  interstices  and  the  percola- 
tion of  water,  it  is  obvious  that  the  size  of  the  finer  particles  rather  than 
the  coarser  determines  its  effective  size.     In  Art.  85  the  term  "effec- 
tive size  "  as  used  in  sand  analysis  was  defined,  as  also  the  measure  of 
uniformity  known  as  the  "  uniformity  coefficient." 

Methods  of  analysis  of  size  are  fully  described  by  Mr.  Hazen  in  the 
Massachusetts  Report  for  1892,  page  541, f  and  in  his  work  on  "Filtra- 
tion of  Water-supplies."  Gravel  is  separated  by  hand-picking  into 
several  sizes,  and  the  average  size  of  each  is  determined  by  weighing. 
Sand  is  separated  by  sets  of  sieves  with  meshes  ranging  from  2  to  200 
per  inch.  The  proportion  of  sand  or  gravel  finer  than  each  particular 
size  is  then  plotted  and  the  effective  size,  or  the  size  corresponding  to 
the  10  per  cent  proportion,  is  readily  found.  Care  must  be  taken  to 
have  the  sand  thoroughly  dry  before  sifting. 

The  separation  size  of  any  particular  sieve  is  found  by  Mr.  Hazen 
by  determining  the  average  diameter  of  the  very  last  particles  to  pass 
the  sieve.  To  compute  this,  the  weight  and  specific  gravity  of  a  known 

*  Deutsche  med.  Wochenschrift,  1891,  No.  25. 
t  See  also  Eng.  Record,  1897,  xxxv.  p.  163. 


4/2  SLOW  SAND   FILTRATION. 

number  of  such  particles  is  determined  and  the  grains  calculated  as 
spheres.  The  actual  size  of  mesh  is  irregular,  and  the  number  of 
meshes  per  inch  is  not  to  be  relied  upon  as  a  measure  of  size. 

For  particles  finer  than  o.  I  mm.  (corresponding  to  a  sieve  with 
about  200  meshes  per  inch)  the  method  of  elutriation  is  used.  In  this 
process,  3  grams  of  sand  are  placed  in  a  beaker  90  mm1,  high  and  hold- 
ing about  230  c.c.,  and  the  beaker  is  then  filled  with  distilled  water 
at  20°  C.  (68°  F.)  The  water  and  sand  are  thoroughly  mixed  and 
allowed  to  stand  15  seconds,  and  the  water  is  then  decanted.  This  is 
repeated  twice  and  the  sand  is  then  weighed.  Experiments  show  that 
this  sand  can  be  considered  as  greater  than  0.08  mm.  in  size.  The 
decanted  sand  is  then  treated  in  a  similar  way,  with  one  minute  for  set- 
tling, and  the  sand  which  settles  calculated  as  greater  than  0.04  mm.  sand. 
The  amount  of  the  portion  below  0.04  mm.  is  estimated  by  difference. 

512.  Selection  of  Sand. — Experiments  show  that  very  fine  sand  is 
considerably  more  efficient  in  removing  bacteria  than  ordinary  or  coarse 
sand,  but  within  the  ordinary  limits  of  size  (0.2  to 0.4  mm.)  the  Lawrence 
experiments  indicate  but  little  difference  in  efficiency.  The  finer 
sands,  however,  cause  a  steadier  action  and  prevent  disturbances  due 
to  scraping ;  they  also  cause  a  greater  loss  of  head  in  the  filter,  and  so 
make  the  action  more  uniform  over  the  filter  area.  On  the  other  hand, 
fine  sand  becomes  clogged  sooner  than  coarse  and  involves  therefore 
more  expense  in  cleaning.  For  waters  containing  very  fine  sediment, 
coarse  filters  are  likely  to  become  clogged  to  a  considerable  depth, 
requiring  the  removal  of  too  thick  a  surface  layer. 

In  practice  the  size  of  sand  used  varies  from  about  O.2  mm.  for 
some  of  the  Holland  dune  sands  to  about  0.4  mm.,  averaging  about 
0.35.*  It  is  desirable  that  a  sand  be  fairly  uniform  in  grain.  If  the 
particles  vary  greatly  in  size,  it  will  be  difficult  to  wash,  and  in  fact  will 
have  much  of  the  finer  particles  removed  in  the  process,  thus  increasing 
the  effective  size.  It  is  especially  important  that  the  sand  should  be 
of  the  same  grade  in  all  parts  of  the  same  filter  in  order  that  the  frictional 
resistance,  and  therefore  the  rate  of  filtration,  shall  be  uniform.  Frequent 
analyses  should  be  made  as  the  sand  is  delivered  at  the  works. 

Regarding  other  requirements,  the  sand  should  be  free  from  clay, 
and  if  necessary  it  should  be  washed.  The  chemical  composition  is 
also  important,  as  a  sand  containing  a  considerable  amount  of  lime  will 
increase  the  hardness  of  the  water.  It  has  also  been  found  that  the 
presence  of  aluminous  and  calcareous  material  increases  very  materially 
the  resistance  to  the  flow  of  water. t 

*  See  analyses  of   sand   from   many   filters   in    Hazen's    "  Filtration   of   Water- 
supplies."  f  Mass.  Report,  1894,  p.  757. 


FRICTION  IN   THE   SAND   LAYER. 


473 


The  specifications  for  the  sand  for  the  Albany  filter-plant,  Allen  Hazen, 
Mem.  Am.  Soc.  C.  E.,  engineer,  were  as  follows : 

"  The  filter  sand  shall  be  clean  river,  beach,  or  bank  sand,  with  either 
sharp  or  rounded  grains.  It  shall  be  entirely  free  from  clay,  dust,  or  organic 
impurities,  and  shall,  if  necessary,  be  washed  to  remove  such  materials  from 
it.  The  grains  shall  all  of  them  be  of  hard  material,  which  will  not  disinte- 
grate, and  shall  be  of  the  following  diameters :  Not  more  than  i  per  cent  by 
weight  less  than  0.13  mm.,  nor  more  than  10  per  cent  less  than  0.27  mm.; 
at  least  10  per  cent  by  weight  shall  be  less  than  0.36  mm.,  and  at  least  70 
per  cent  by  weight  shall  be  less  than  i  mm.,  and  no  particles  shall  be 
more  than  5  mm.  in  diameter.  The  diameters  of  the  sand  grains  will  be 
computed  as  the  diameters  of  spheres  of  equal  volume.  The  sand  shall  not 
contain  more  than  2  per  cent,  by  weight,  of  lime  and  magnesia  taken  together 
and  calculated  as  carbonates." 

Where  it  is  necessary  to  wash  the  sand  a  standard  for  this  work  must  be 
adopted.  At  Washington  a  turbidity  standard  was  required  equivalent  to 
about  0.2  per  cent  of  clay.  At  Pittsburg  the  specifications  required  that  100 
grains  of  sand  shaken  in  one  liter  of  water  should  not  cause  a  turbidity 
greater  than  200  parts  per  million,  silica  standard. 

513.  Friction  in  the  Sand  Layer.  —  From  Art.  85  the  rate  of  filtra- 
tion through  sand  is 


where  V  =  velocity  of  water  in  meters  daily  in  a  solid  column ; 
c  =  a  coefficient,  equal  to  400  to  1000 ; 
d  =  effective  size  of  sand ; 
h  =  head  causing  flow ; 
/  =  depth  of  sand  layer  ;  and 
t  =s  temperature  in  degrees  Fahrenheit. 

Using  a  value  of  c  of  800  the  following  table  of  losses  of  head,  or 
values  of  //,  has  been  calculated  for  a  filter  i  foot  thick 

TABLE   NO.  69. 

FRICTIONAL  HEAD   IN   FEET,    IN   COMPACTED    SAND   ONE    FOOT   THICK,    AT   A 

TEMPERATURE    OF    50°    F. 


Rate  of  Filtration,  Millions  of  Gallons  per  Acre  per  Day. 


Size  of  Sand  Millimeters. 

I 

4 

2 

4 

3 

si 

4 

4* 

5 

I  e 

OC2 

078 

1  04. 

I  30 

is6 

182 

2O8 

234 

260 

20         

O^O 

04? 

060 

O7C 

OQO 

10^ 

I2O 

?•*$•* 

T  2  C 

I  ^O 

2C     . 

.OIO 

.028 

.0^8 

.  047 

o<;6 

.06^ 

•ws 

O7C 

O84 

OQ4 

.OI3 

.020 

.026 

.033 

•  O7Q 

046 

.OtC2 

.0^8 

.065 

•?r 

OIO 

OI4 

OIO 

O24 

020 

O?4 

O34 

O42. 

048 

4O 

007 

.  OI  I 

OI4 

018 

022 

026 

O2O 

<V-^M 
o?-? 

O37 

•^oo 

474 


SLOW  SAND   FILTRATION. 


The  effect  of  temperature  on  the  resistance  is  very  marked,  the  loss 
of  head  at  40°  being  20  per  cent  higher,  at  60°  about  14  per  cent 
lower,  and  at  70°  25  per  cent  lower  than  the  above  figures. 

The  loss  of  head  in  a  freshly  cleaned  filter  composed  of  a  o.3O-mm. 
sand,  4  feet  deep,  and  filtering  at  a  rate  of  3  million  gallons  per  acre  per 
day,  will  be,  according  to  this  table,  approximately.  039x4— .156  feet, 
or  about  2  inches.  In  the  winter  it  will  be  more  and  in  the  summer 
less.  After  a  filter  has  been  in  use  for  some  time  after  cleaning,  the 
effect  of  clogging  is  of  course  to  cause  a  loss  of  head  many  times 
greater  than  these  figures. 

514.  Thickness  of  Sand  Bed. — In  the  older  filters  great  variations 
exist  in  the  thickness  of  the  several  layers  of  sand  and  gravel,  and  in 

the  depth  of  water  on  the  filter.  Fig. 
124  shows  the  make-up  of  many  filters 
abroad  and  illustrates  this  lack  of  uni- 
formity. It  will  be  seen  that  the  thick- 
ness of  sand  is  usually  from  2  to  3  feet, 
the  gravel  layer  about  the  same,  and 
the  depth  of  water  about  3  or  4  feet. 
In  some  filters  a  layer  of  fine  sand  is 
underlain  by  a  thick  layer  of  coarse. 

In  designing  a  filter  it  should  be 
noted  that  the  sand  forms  the  filtering 
medium;  the  gravel  serves  simply  to 
collect  the  filtered  water  with  little 
'resistance  to  flow.  There  is  no  object 


Great  Britain  &  Ireland* 


Oermany.^ 


Netherlands 


FIG.  124. — MAKE-UP  OF  FOREIGN  FILTERS. 

(From  Engineering  News,  vol.  xxviu.) 

in  having  the  main  body  of  sand  of  different  sizes  unless  it  happens  that 


DRAINAGE   SYSTEMS.  475 

a  sand  of  the  fineness  desired  for  the  upper  portion  of  the  bed  is  expen- 
sive, in  which  case  a  coarser  sand  may  be  used  for  a  considerable  thick- 
ness next  to  the  gravel.  A  fine  sand  should  never  be  placed  below  a 
coarser  one,  as  this  will  cause  subsurface  clogging. 

The  original  depth  of  sand  must  be  sufficient  to  form  an  effective 
filter  and,  besides,  to  allow  of  several  scrapings  without  the  renewal  of 
the  sand.  Inasmuch  as  the  bacterial  efficiency  depends  in  part  on  the 
action  which  takes  place  in  the  body  of  the  filter  (Art.  494),  and  not 
exclusively  at  the  surface,  an  increase  in  depth  within  certain  limits  will 
tend  to  increase  the  efficiency  of  the  filter.  The  Imperial  German 
Board  of  Health  requires  as  a  minimum  at  least  1 2  inches,  but  in  actual 
practice  the  beds  are  considerably  thicker.  The  effect  of  deep  beds  is 
similar  to  that  of  fine  sand  in  steadying  the  action  of  a  filter,  and  it  has 
been  clearly  shown  by  the  Lawrence  experiments  that  the  operation  of 
beds  4  to  5  feet  thick  is  not  so  much  affected  as  that  of  beds  I  to  2  feet 
thick  by  such  disturbances  as  variations  in  rate,  scraping  of  beds,  etc., 
although  the  results  with  perfectly  uniform  conditions  are  not  materially 
different.  The  effect  of  depth  is  also  very  important  in  causing  a  more 
uniform  action  over  the  entire  bed  of  a  freshly  cleaned  filter  by  mini- 
mizing the  effect  of  frictional  resistance  in  the  under-drains. 

For  the  foregoing  reasons  it  would  seem  desirable  to  adopt  a  mini- 
mum thickness  of  at  least  2  feet,  and  to  make  the  bed  originally  3  feet 
thick.  In  several  filters  recently  constructed  the  original  depth  of  sand 
is  4  feet. 

515.  The  Depth  of  Water  on  the  Filter  should  be  sufficient  to  enable 
the  desired  maximum  head  to  be  used  without  reducing  the  pressure 
in^the  filter  below  atmospheric;  and  as  the  resistance  is  nearly  all  at 
the  surface  of  the  sand,  the  depth  must  be  about  equal  to  the  maximum 
head  used.     (Art.  520.)     Certain  experiments  have  shown  that  "nega- 
tive heads  "  are  likely  to  cause  the  liberation  in  the  filter    of   some 
of  the  air  dissolved  in  the   water  and  so   cause    disturbances.      The 
depth  must  also  be  greater  than  the  thickest  ice  likely  to  form.     Beyond 
these  limiting  depths  any  increase  serves  only  to  increase  the  expense 
of  construction. 

5 16.  Drainage  Systems.  —  To  collect  the  filtered  water  a  system  of 
under-drains  is  necessary.     The  important  points  to  be  considered  in 
its  design  are  durability  and  freedom  from  derangement,  and  that  the 
loss  of  head  therein  shall  be  small.     The  system  of  drains  usually  con- 
sists of  a  large  central  drain  running  the  length  of  the  filter,  and  branch 
drains  at  right  angles  thereto  placed  at  regular  intervals,  usually  of 
8  to  12  feet.     The  central  drain  may  be  made  either  of  large  vitrified 


476  SLOW  SAND  FILTRATION. 

pipe  or  of  concrete  ;  the  branch  drains  are  usually  of  4-  to  8 -inch  round 
or  special  tile,  laid  with  open  joints. 

To  avoid  using  a  very  large  amount  of  gravel  filling  in  order  to  form 
a  level  surface  for  the  sand  bed,  the  main  drain  should  be  sunk  into  the 
floor  of  the  filter  so  that  its  top  is  no  higher  than  the  laterals.  For  the 
same  reason  the  floor  of  the  filter  is  sometimes  made  wavy  in  section 
and  the  laterals  are  placed  in  the  depressions  so  formed.  Various 
arrangements  are  illustrated  in  Figs.  125  to  128. 

To  conduct  the  water  to  the  lateral  drains,  coarse  gravel  an  inch 
or  two  in  diameter  is  filled  about  the  drains  and  spread  in  a  layer  of 
6  inches  or  more  in  depth  evenly  over  the  floor  of  the  filter,  or,  if  the 
bottom  of  the  filter  is  irregular,  it  may  be  arranged  as  shown  in  Fig. 
127.  Above  this  coarse  gravel  are  then  placed  three  or  four  layers  of 
finer  gravel,  each  successive  layer  being  finer  in  size,  but  not  so  fine  as  to 
settle  into  the  previously  laid  layer.  The  last  layer  is  made  fine  enough 
to  support  the  sand.  The  thickness  of  these  layers  need  be  only  2  or 
3  inches  if  carefully  laid,  or  just  sufficient  to  insure  that  the  next  layer 
below  is  well  covered.  In  many  of  the  old  filters  as  much  as  3  or  4 
feet  of  gravel  was  used,  with  very  large  sizes  at  the  bottom,  but  as  it 
has  little  or  no  duty  except  to  act  as  a  drain,  any  depth  above  what  is 
needed  for  this  purpose  only  adds  to  the  expense  of  construction.  It 
will  be  seen  that  the  frictional  resistance  in  gravel  only  I  or  2  inches 
in  diameter  is  very  small  at  the  velocities  which  obtain. 

The  gravel  used  should  be  carefully  screened  and,  if  dirty,  washed. 
It  is  readily  sized  by  revolving  or  fixed  screens,  using  for  this  purpose 
three  or  four  different  sizes.  The  smallest  should  have  about  a  Ts^-inch 
mesh,  and  each  larger  size  about  double  the  size  of  mesh  of  the  next  pre- 
ceding. At  Albany  the  sieves  used  were  T3^,  f,  I,  and  3  inches  respec- 
tively, all  of  the  gravel  being  required  to  pass  through  the  3 -inch  sieve. 

517,  Special  Arrangements. — In  some  cases,  in  place  of  lateral 
drains  covered  by  a  deep  layer  of  gravel,  a  cellular  floor  is  used.  This 
may  be  made  by  laying  brick  flatwise,  with  narrow  open  joints,  upon 
other  brick  placed  at  right  angles  thereto,  an  arrangement  which 
requires  but  little  gravel  and  occupies  but  little  space  in  the  filter.  In 
other  cases,  drain-tile  has  been  laid  at  right  angles  to  the  main  drain 
so  as  to  cover  the  entire  bottom.  Still  other  arrangements  have  been 
employed  and  various  special  tile  used.  The  only  office  of  the  drainage 
system  is  to  furnish  a  channel  for  the  flow  of  the  water  with  a  certain 
minimum  loss  of  head,  and  that  arrangement  should  be  used  which  will 
accomplish  this  in  the  most  economical  manner  and  leave  a  level  bed 
for  the  sand  layer. 


DRAINAGE  SYSTEMS. 


477 


518.  Examples.  —  Fig.  125  illustrates  the  drainage  arrangement  of  the 
Hamburg  beds.  The  niters  have  an  area  of  1.89  acres  each.  The  central 
drain  is  22  by  32  inches,  with  brick  sides  and  masonry  cover.  The  laterals 
are  6  inches  wide  and  7^  inches  high,  and  are  spaced  about  30  feet  apart 
The  gravel  layer  is  2  feet  thick.  * 


••••  ;.. 

•:?:l:.-'{\r£&:£<5(7/X/ 


FIG.   125. —  SECTION  OF  HAMBURG  FILTER. 

The  arrangement  of  drains  in  the  Albany  plant  is  shown  in  Fig.  120,  page 
465,  and  sections  through  a  main  drain  and  laterals  in  Fig.  126.     The  filter 


El.  121.5^ A 


2  Sheet  Steel  Covers 
2  inch  Air  Spa«e 


Section  through  Main  Drain. 


Pier-, 


Section  through  Lateral. 
FIG.   126. —  DETAILS  OF  DRAINS,  ALBANY  FILTER-BEDS. 

(From  Trans.  Am.  Soc.  C.  E.,  vol.  XLIII.) 

is  covered,  and  a  6-inch  lateral  is  laid  in  each  space  between  the  rows  of  piers. 
The  drains  are  of  vitrified  pipe,  the  laterals  being  laid  with  open  joints. 

Fig.  128  is  a  plan  of  bed  and  a  section  through  the  central  drain  of  one  of 


Meyer.     Das  Wasserwerks  Hamburg,  p.  19. 


478 


SLOW  SAND  FILTRATION. 


the  Zurich  filters.     The  main  drain  is  of  concrete,  and  the  laterals  are  of  tile 
laid  over  the  entire  floor.* 

Fig.  127  shows  the  general  design  and  drainage  system  of  one  of  the 
large  Philadelphia  plants.  The  arrangement  is  quite  similar  to  that  at 
Albany,  but  the  more  general  use  of  concrete  should  be  noted. 


FIG.   127. — DRAINAGE  SYSTEM  LOWER  ROXBOROUGH  PLANT,  PHILADELPHIA. 

(From  Engineering  Record \  vol.  XLII.) 

519.  Loss  of  Head  in  the  Drainage  System.  — The  total  loss  of  head 
in  the  filter  is  equal  to  the  loss  of  head  in  the  sand  plus  that  in  the 
under-drains.  That  in  the  sand  is  uniform  throughout  the  filter,  but  in 


FIG.  128. — FILTER-BED  AND  DRAIN  DETAILS,  ZURICH. 

(From  Engineering  Record,  vol.  xxxix.) 

the  under-drains   it   varies   from   zero   near  the  outlet  to  a  maximum 

for  the  most  remote  point.     The  rate  of  filtration  will  be  proportional 

to  the  total  head  and  therefore  will  vary  in  different  parts  of  the  bed. 

*  Eng.  Record,  1899,  xxxix.  p.  472. 


DRAINAGE  SYSTEMS. 


479 


The  loss  of  head  in  the  drains  should  be  kept  so  low  that  with  a  clean 
filter  the  variation  in  the  rate  of  filtration  in  different  parts  of  the  bed 
will  not  be  excessive.  A  variation  of  20  to  25  per  cent  would  not  be 
a  serious  matter,  as  the  excess  above  the  average  would  then  be  only 
10  or  12  per  cent.  Furthermore,  this  difference  would  occur  for  only 
a  short  time  after  cleaning,  for  as  a  filter  becomes  clogged  the  relative 
difference  in  heads  is  much  less. 

If  we  take,  for  example,  a  filter  composed  of  .30  mm.  sand,  depth 
4  feet,  rate  of  filtration  3  million  gallons  per  acre  per  day,  the  loss  of 
head  due  to  the  sand  alone  when  the  filter  is  clean  will  be  about  .039 
X  4  =-156  foot.  If  we  allow  a  maximum  loss  of,  say,  one-fifth  of  this 
for  the  drains,  or  .031  foot,  the  total  head  will  then  vary  from  .  156  to 
.187,  and  the  rate  of  filtration  will  vary  about  10  per  cent  above  and 
10  per  cent  below  the  average.  To  keep  the  loss  of  head  in  the  drains 
to  this  low  limit  requires  the  use  of  low  velocities  and  relatively  large 
pipes. 

The  loss  of  head  in  drains  according  to  Kutter's  formula  is  given 
in  Table  No.  70.  The  loss  of  head  in  gravel  per  foot  of  distance  is 
approximately  given  in  Table  No.  71.* 

TABLE   NO.  70. 

FRICTIONAL   HEAD    IN    DRAINS,  IN    FEET   PER    IOO   FEET   OF    DRAIN. 


Diameter  of  Drain  in  Inches. 

Discharge. 
Gallons  per  Day. 

Velocity. 
Feet 
per  Sec. 

4 

6 

8 

10 

12 

15 

18 

20 

«4 

3° 

7ooX(diam.)2 

.2 

.012 

.006 

.004 

1400"      " 

•4 

.050 

.025 

.016 

.Oil 

.OOQ 

.006 

.005 

.004 

.003 

.002 

2TCO"        " 

.6 

•113 

•057 

.036 

.025 

.Oig 

.014 

.Oil 

.009 

.007 

.005 

2800"      " 

.8 

.202 

.IOI 

.064 

•045 

•035 

.025 

.OI9 

.016 

.012 

.009 

3500"      " 

I.O 

•3^5 

.158 

.IOO 

.070 

•054 

•039 

•030 

.025 

.OI9 

.014 

TABLE  NO.  71. 

FRICTIONAL   HEAD    IN    GRAVEL    PER    FOOT    OF    DISTANCE. 


Rate  of  Flow. 

Effective  Size  of  Gravel  in  Millimeters. 

Gals,  per  Day 

per  Square  Foot 
of  Cross-section 

10 

20 

30 

4° 

500 

.00035 

.OOOI2 

IOOO 

.0007 

.00025 

2000 

.0014 

.0005 

.00025 

300O 

.OO22 

.0008 

.00037 

.OOO25 

*  Based  on  results  of  experiments  of  Mass.  Bd.  Health,  Report  for   1892,  p.  555 


480  SLOW  SAND   FILTRATION1. 

The  loss  of  head  in  the  gravel  can  be  kept  low  either  by  means  of 
a  thick  layer,  or  by  putting  the  drains  close  together.  Wide  spacing 
requires  fewer  drains,  but  larger  sizes  and  more  gravel.  When  the  cost 
of  drains  and  gravel  is  known,  the  most  economical  arrangement  for  a 
given  loss  of  head  can  be  determined  by  a  few  trials. 

Thus  with  a  rate  of  3  million  gallons  per  acre  per  day  (equal  to 
about  75  gallons  per  square  foot  per  day),  and  drains  20  feet  apart,  the 
total  flow  through  each  foot  of  width  of  gravel  will  beioX75=75O 
gallons.  With  6  inches  of  20  mm.  gravel  the  average  flow  per  square 
foot  will  be  2  X  750  =  1500  gallons,  and  by  the  above  table  the  loss 
of  head  is  seen  to  be  about  .00037  f°ot  Per  f°ot-  The  average  distance 
travelled  is  5  feet,  hence  the  total  loss  of  head  in  the  gravel  will  be 
.0018  foot.  ,  This  is  a  very  small  loss  and  would  usually  be  much 
smaller  than  necessary.  A  still  thinner  layer  of  gravel  might  therefore 
be  used,  or  the  drains  placed  farther  apart. 

The  maximum  length  of  drain  (main  and  lateral)  for  beds  of  one 
acre  in  area  will  be  about  350  feet.  If  the  total  loss  is  to  be  kept  down 
to,  say,  .03  foot,  this  will  allow  but  about  .008  foot  per  hundred  feet  in 
the  drains.  Inspection  of  Table  No.  70  will  show  that  it  will  be 
necessary  to  use  velocities  of  .2  to  .3  foot  per  second  in  laterals,  and 
.6  to  .8  foot  in  main  drains.  The  necessary  size  for  any  given  capacity 
is  readily  computed.  The  size  of  main  drain  should  increase  towards 
the  outlet.  In  the  above  example,  6-inch  laterals  20  feet  apart  would 
themselves  consume  about  .023  foot  of  head,  an  amount  too  large  where 
the  total  allowable  loss  is  only  .03  foot.  Eight-inch  drains  20  feet 
apart  would  use  only  .0035  foot,  leaving  about  .026  foot  for  the  main 
drain.  This  can  then  be  made  up  of  sizes  varying  from  12  to  30 
inches.  With  thin  beds  of  coarse  sand  the  difficulty  of  maintaining 
uniform  rates  is  evidently  much  increased. 

In  the  Washington  filters  the  loss  of  head  in  the  various  parts  of  the 
filter  is  equalized  by  the  use  of  brass  orifices  of  different  sizes  inserted 
at  the  points  of  connection  between  main  and  lateral  drains.  This 
arrangement  permits  the  use  of  a  smaller  main  drain  than  would  other- 
wise be  necessary.* 

520.  Maximum  Total  Loss  of  Head.  —  As  a  filter  becomes  clogged 
the  head  necessary  to  cause  filtration  at  the  assumed  rate  increases. 
By  allowing  the  head  to  increase  to  a  high  figure  the  filter  can  be 
operated  longer  without  scraping  and  so  a  saving  in  operation  effected. 
On  the  other  hand  high  losses  of  head  require  more  pumping,  a 

*  Trans.  Am.  Soc.  C.  E.  1906,  LVII.  p.  325. 


INLET-PIPES. 


481 


greater  depth  of  filter,  and  have  a  detrimental  effect  in  compacting  the 
sand.  The  efficiency  of  the  filter  is  little  affected.  Experiments  of  the 
Massachusetts  Board  show  that  heads  of  70  inches,  constantly  used 
there,  give  substantially  the  same  bacterial  efficiency  as  lower  heads. 
Many  filters  in  use  also  operate  under  heads  of  4  or  5  feet  with  good 
results,  and  there  appears  to  be  no  good  reason  for  using  less  than  this. 
Much  higher  heads  would  probably  not  be  economical.  Results  of 
operation  and  experiment  show  in  some  cases  an  increase  in  time 
between  scraping  proportional  to  the  maximum  head  used,  and  in  other 
cases  the  gain  in  time  is  much  less  proportionally  than  the  increase 
in  maximum  loss  of  head. 

521.  Inlet-pipes.  —  Water  is  admitted  to  the  filter  through  a  single 
branch  main  at  about  the  level  of  the  surface  of  the  sand.     The  flow  is 
usually  controlled  by  a  balanced 

valve  operated  by  a  float,  so  as  to 
maintain  the  water  in  the  filter 
at  a  constant  level.  A  gate-valve 
is  provided  in  addition,  to  enable 
the  water  to  be  completely  shut 
off  at  any  time.  Fig.  129  illus- 
trates the  balanced  float-valve 
and  details  at  one  of  the  large 
Philadelphia  plants,  while  Fig. 
1  30  shows  in  detail  a  somewhat 
different  form  designed  by  Mr. 

D.  W.  Mead  for  the  filters  at 

•n      i    T  i      j   Tii       T>  -IT 

KOCK  Island,  111.        iO  avoid  dlS- 

turbing  the  sand  as  much  as  possible  the  water  should  flow  upon  the 
bed  at  a  low  velocity,  and  a  common  arrangement  is  to  provide  a 
broad  weir,  as  shown  in  Figs.  128  and  129,  over  which  the  water  passes. 
On  filling  the  filter  after  cleaning,  it  is  necessary  then  to  fill  from  below 
only  slightly  above  the  surface  of  the  sand  before  turning  on  the 
unfiltered  water. 

In  place  of  providing  a  regulating-valve  for  each  filter  the  influent 
pipes  may  all  lead  from  a  central  regulating-well  in  which  the  water- 
level  is  maintained  constant.  Such  an  arrangement  is  suited  to  a 
compact  group  of  small  filters. 

522.  Outlet-pipes  and  Apparatus  for  Regulating  the  Head.  —  If  the 
water-level  on  the  filter  is  kept  constant,  the  rate  of  filtration  must  be 
regulated,  as  the  filter   becomes  clogged,  by  lowering  the  water-level 
or  reducing  the  pressure  at  the  outlet.     In  the  older  filters  no  arrange- 


FIG.  129.  —  INLET  REGULATOR  USED  AT 

PHILADELPHIA. 
(YromE*gitu9ri*fR*c<>rdtv<A.xi.ii.) 


482 


SLO  W  SAND  FIL  TRA  TIOM 


ment  was  provided  for  regulating  each  filter  independently,  but  each 
was  connected  to  the  clear-water  well  by  a  short  pipe  fitted  with  an 
ordinary  valve.  The  head  on  all  filters  was  consequently  always  the 
same,  except  as  it  might  be  controlled  by  throttling  at  the  valves- 
The  effect  of  unequal  heads  on  the  rate  of  filtration,  where  some  of  the 
filters  might  be  freshly  cleaned  and  others  badly  clogged,  can  readily 
be  imagined.  Independence  of  action,  especially  as  respects  maximum 
rate,  is  greatly  to  be  desired  and  is  now  the  general  practice. 

The    regulation   of   head  requires,   first,   some  form  of    measuring 
device,  such  as  a  weir,  orifice,  or  Venturi  meter  by  which  the  rate  of 


FIG.  130. —  REGULATING-VALVE,  ROCK  ISLAND  FILTERS. 

filtration  can  be  ascertained  at  any  time  by  floats  and  indicators ;  and, 
second,  the  controlling  of  the  rate  of  flow  either  by  hand  or  automati- 
cally. Floats  are  also  required  to  show  the  level  on  the  filter  and  the 
head  in  the  main  drain,  the  difference  of  which  is  the  working  head  on 
the  filter.  The  apparatus  for  regulation  is  placed  in  one  or  more 
chambers  with  which  the  main  drain  of  the  filter  connects. 

523.  Hand  Regulation.  —  If  a  weir  or  orifice  is  used  the  rate  of  flow 
may  be  regulated  by  lowering  the  weir  or  orifice  itself  as  the  beds 
become  clogged,  or  by  varying  the  opening  in  a  valve  connecting  the 
main  drain  with  the  weir  chamber.  In  either  case  the  object  sought  is 
to  maintain  a  constant  head  on  the  weir  or  orifice. 


REGULATION  OF  FILTERS. 


483 


The  first  plan  is  that  followed  at  Hamburg,  the  regulating  arrange- 
ments for  which  are  shown  in  Fig.  131.  The  head  on  the  filter  at  any 
time  is  the  difference  in  level  between  the  water  in  the  filter  and  that 
in  the  main  drain  and  chamber  connecting  therewith ;  it  is  indicated  by 
suitable  floats.  The  head  on  the  weir,  or  the  rate  of  filtration,  is  also 
indicated  by  floats,  and  is  kept  constant  by  moving  the  weir  from  time 
to  time  as  the  filter  becomes  clogged.  Instead  of  a  weir  like  that  shown 
in  Fig.  131,  a  telescopic  tube  has  been  used  in  some  places,  similar  to 
the  form  shown  in  Fig.  134,  but  adjusted  by  hand. 

In  the  Albany  plant  and  the  plant  at  Yonkers  the  second  method  is 
adopted,  a  fixed  orifice  being  used.  The  design  at  Albany  is  illustrated 


FIG.  131. —  REGULATING-APPARATUS  AT  HAMBURG. 

in  Fig.  132.  The  measuring  is  done  by  means  of  an  orifice  in  a  wooden 
partition,  a  head  of  I  foot  on  this  orifice  being  necessary  to  pass  the 
standard  quantity  of  water.  This  head  is  varied  by  means  of  the  gate- 
valve  admitting  water  from  the  under-drains.  The  actual  head  on  the 
filter  is  measured  by  the  difference  between  the  water-level  in  the  filter 
and  the  pressure-head  in  the  pipe  just  back  of  this  valve.  Small  float- 
chambers  are  provided,^  connecting  with  the  different  points,  and  suit- 
able floats  indicate  the  loss  of  head  and  the  rate  of  filtration.  When 
the  rate  of  filtration  exceeds  the  demand,  the  level  of  the  water  in  the 
clear-water  well  gradually  rises  above  the  orifice,  thus  decreasing  the 
rate  to  correspond  to  the  reduced  demand.  This  arrangement  was 
adopted  on  account  of  the  small  size  of  the  clear-water  reservoir  which 
local  conditions  made  necessary.  Only  so  much  capacity  was  provided 
as  was  necessary  to  give  a  reasonable  time  for  the  filters  to  respond  to 
the  variations  in  the  demand.  The  advantage  of  this  arrangement  is 


484 


SLOW  SAND  FILTRATION. 


a  smaller  loss  of  head  in  the  system,  a  smaller  clear-water  reservoir, 
and  a  partial  automatic  regulation  of  the  filters  to  furnish  the  desired 
quantity  of  water. 

Several  of  the  most  recent  plants  have  used  the  Venturi  meter  for 
the  measuring  device,  controlling  the  rate  of  flow  by  hand.  This  makes 
a  very  satisfactory  and  compact  arrangement.  Fig.  133  illustrates  this 
arrangement  as  used  at  Washington,  D.  C.  Here  the  effluent  pipes 
from  four  filters  are  led  to  a  single  chamber.  In  the  design  of  Fig.  1 34 
the  Venturi  meter  is  used  in  addition  to  the  automatic  regulator. 

524.  Automatic  Regulation.  —  Automatic  regulators  for  delivering 
water  at  a  constant  rate  are  in  use  in  a  number  of  places.  They  usually 


FIG.  132.  —  REGULATING  CHAMBER,  ALBANY  FILTER-BEDS. 

(From  Trans.  Am.  Soc.  C.  E.  vol.  XLIII.) 

consist  of  a  weir  in  the  form  of  a  telescopic  tube  which  is  supported  by 
means  of  a  float  in  the  chamber  connecting  with  the  under-drain.  By 
adjusting  the  float,  the  edge  of  the  weir  can  be  maintained  at  any  desired 
distance  below  the  water-surface.  A  weir  of  this  general  type  is  illus- 
trated in  Fig.  134.  The  rate  of  discharge  is  varied  by  changing  the 
relative  height  of  float  and  weir.  A  variation  of  this  form  is  used  at 
Pittsburg.  Here  the  movement  of  the  telescopic  tube  and  float  is 
arranged  to  operate  a  balanced  piston  valve  in  the  pipe  leading  from 
the  under-drain.  By  this  means  a  very  slight  movement  of  the  float  is 
sufficient  to  regulate  the  loss  of  head  and  the  rate  of  filtration.  A 
difficulty  connected  with  the  use  of  the  open  weir  is  caused  by  the 
drawing  into  the  pit  of  a  large  amount  of  air  with  the  water.  This  may 


REGULATION  OF  FILTERS. 


485 


be  obviated  by  using  a  submerged  orifice.  A  form  of  balanced  pressure- 
valve  devised  by  Burton  *  and  used  for  automatic  regulation  is  illustrated 
in  Fig.  135.  The  quantity  of  water  passing  the  valve  is  maintained 
constant  by  keeping  the  difference  of  pressure  on  the  two  sides  of  an 


T.  C.L.(1M.3 
16' Refill  Elev.O 
20'Filtered-Wator  Efilu«t  _ 


NOTE: 

Detail  arrangements  differ  slightly 
\  in  the  different  houses. 


PLAN  AND  SECTIONS 

REGULATOR  HOUSES 


20'  Filtered- Water 
Effluent  1 


SECTION  ON  D-D 

FIG.  133.  —  REGULATING  CHAMBERS,  WASHINGTON,  D.  C. 

(From  Trans.  Am.  Soc.  C.  E.,  vol.  LVII.) 

orifice  in  the  plate  e  a  constant  quantity.  This  is  done  automatically  by 
the  balanced  valve  c,  controlled  by  the  piston  d,  which  is  open  to  water- 
pressure  both  from  the  outside  well  and  from  the  valve-chamber.  A 
somewhat  similar  form  is  shown  in  Fig.  I38k,  of  the  next  chapter.f 

*  Proc.  Inst.  C.  E.,  cxn.  p.  321. 

t  See  paper  by  Anthony  on  Automatic  Modules,  Trans.  Am.  Soc.  C.  E.,  1903, 
LI.  p.  136. 


486 


SLOW  SAND  FIL TRA  TION. 


525.  Other  Pipes  and  Valves. —  Besides  the  inlet-  and  outlet-pipes, 
a  drain-pipe  must  be  provided  through  which  the  water  may  be  drawn 
off.  This  is  usually  connected  with  the  chamber  into  which  the  main 
drain  opens,  as  shown  in  Figs.  133  and  134.  An  overflow-pipe  is  also 


Meter  Tube  in  Main  Collector. 


Raw  Water 
Indicator  Met. 


FIG.  134.    AUTOMATIC  REGULATOR.     PHILADELPHIA. 

(From  Engineering  Record,  vol.  XLII.) 

necessary  to  provide  against  any  failure  on  the  part  of  the  inlet-regu- 
lator.    This  connects  with  the  drain-pipe.     (See  also  Fig.  128.) 

After  a  filter  has  been  drained  and  cleaned  it  is  desirable  to  fill 
with  filtered  water  from  below  to  a  short  distance  above  the  sand.     If 

the  water  in  the  pure-water  basin  is 
at  a  level  higher  than  the  surface  of 
the  sand,  water  can  be  admitted  from 
it  to  the  under-drains  by  means  of  a 
by-pass  around  the  regulating-appara- 
tus or  through  the  partition-wall.  If 
the  pure-water  basin  is  too  low  for 
tn^  water  mav  ke  piped  from  an 
adjoining  filter  which  is  in  operation. 
Arrangements  should  be  made  for 
wasting  the  filtered  water  in  case  it 
should  be  necessary,  also  for  drawing 
off  the  water  from  above  a  filter  down 
close  to  the  sand  layer  in  order  to  save  time  in  emptying  •  and  facili- 
ties should  be  provided  for  sampling  water  from  various  points  in  the 
system.  By-passes  should  be  provided  to  enable  either  settling-basin 
or  filters  to  be  cut  out  if  necessity  arises.  For  furnishing  water  for 


FIG.  135. —  AUTOMATIC  REGULATING- 
VALVE.     (BURTON). 


CLEANING  FILTERS.  487 

sand-washing  and  various  purposes,  connection  must  be  made  with  high- 
pressure  mains. 

526.  General  Arrangement  of  Piping.  —  The  location  of  main  supply- 
pipe,    effluent-pipe,    and    drain    varies    according   to    local    conditions. 
At  Albany  (Fig.  120)  the  supply-pipes  and  inlet-chambers  are  placed 
along  one  end  of  the  beds,  while  effluent-  and  drain-pipes,  with  regu- 
lating-chambers,   are    placed   along   the    other    end.     At    Hamburg  a 
similar   arrangement    is   adopted.     At    other  places,  as  at   Berlin,  all 
pipes  and  chambers  are  placed  along  one  side  of  the  group  of  filters. 
This  is  a  more  compact  arrangement,  and  is  the  more  common  one  in 
modern  plants.     For  convenience  of  operation,  several  filters,  two  to 
six,  should  be  operated  from  a  single  regulating  house.     This  concen- 
trates   the    operating   mechanism    and    aids    in    supervision.     Covered 
valve-chambers  or  gate-houses  should  be  provided  with  open  filters  as 
well  as  with  closed. 

527.  Pure-water  Reservoir.  —  Where  practicable  a  pure- water  reser- 
voir should  be  provided  of  sufficient  capacity  to  prevent  the  necessity 
of  frequent  variations  in  the  rate  of  filtration.      If  this  is  not  done,  it  is 
at  least  necessary  to  furnish  a  capacious  pump-well  to  prevent  the  fluc- 
tuations of  the  pumps  from  being  directly  felt  by  the  filters.     To  enable 
the  filters  to  be  independently  regulated  the  highest  level  in  the  pure- 
water  reservoir  should  always  be  lower  than  the  level  of  the  water  in 
the  regulating-chambers  of  the  filter.     This  may  not  always  be  practi- 
cable, as  at  Albany.     From  the  data  of  Chapter  II,  Art.  31,  it  will  be 
found  that  to  equalize  the  supply  for  an  ordinary  day  requires  usually 
from  two  to  three  hours'  average  consumption,  and  if  the  pure-water 
reservoir  is  given  this  capacity,  plus  a  moderate  fire  reserve,  it  will  be 
necessary  to  vary  the  rate  of  the  filters  but  slightly  from  day  to  day. 

528.  Cleaning  Filters.  —  When  a  filter  has  become  clogged  and  has 
reached   its   highest    allowable   loss    of   head,  it    is    drained  and  then 
cleaned  by  removing  the  layer  of  clogged  sand  which  is  usually  from  \ 
to    I  \  inches   thick.     The  scraping  is  ordinarily  done  by  using  broad, 
thin  shovels,  but  at  Pittsburg  a  sand  scraping  machine  has  been  adopted 
which  is  expected  to  be  more  economical.     A  distributing  machine  is 
also  to  be  used   there.*      Sand  is  removed  by  wheelbarrows,   or,   as 
now  more  generally  done,  by  portable  ejectors  (see  Art.  532)  to  sand 
washers  where  it  is   cleaned  and   stored  or  returned  to  another  bed. 
After  scraping,  the  filter  is  filled,  preferably  from  below,  with  filtered 
water  until  covered  2  or  3  inches  deep ;  then  raw  water  is  run  on  to  the 

*  Eng.  Record,  1906,  LIV,  p.  664. 


488  SLO  W  SAND  FIL  TRA  TION. 

usual  depth,  and  the  filter  again  started  into  action.  At  intervals  of  a 
year  or  so,  and  before  the  layer  of  sand  has  been  reduced  below  a 
desirable  minimum  thickness,  the  bed  is  restored  to  its  original  depth 
by  the  addition  of  clean  sand.  The  minimum  thickness  allowable  by 
the  German  rule  is  12  inches,  but  a  considerably  greater  thickness  is 
to  be  preferred  for  the  reasons  already  given  in  Art.  514.  At  the  last 
cleaning  before  refilling,  a  thicker  layer  than  usual  should  be  removed, 
and  the  remaining  sand  to  a  depth  of  several  inches  dug  over  and 
loosened.  This  procedure  is  to  avoid  the  effect  of  stratification  and  to 
aerate  the  filter  to  some  extent.  At  some  works  it  is  the  practice  to 
occasionally  remove  all  the  remaining  sand  and  even  the  gravel.  After 
cleaning  and  filling,  the  filter  should  be  started  slowly  and  gradually. 
At  some  works  it  has  been  found  beneficial  to  allow  the  raw  water  to 
stand  upon  the  filter  for  several  hours  before  operation  begins,  in  order 
that  some  sediment  may  collect  on  the  surface  and  so  hasten  the  estab- 
lishment of  the  surface  sediment  layer. 

529.  Cleaning  Open  Filters  in  Winter. — To  accomplish  this  properly 
is  the  chief  difficulty  in  operating  open  filters.     If  the  ice  is  removed 
and  the  filter  drained  and  cleaned  in  the  usual  way,  there  is  much 
danger  that  the   sand  will  be  frozen   and  the  operation  of  the  filter 
greatly  interfered  with.     It  may  also  be  very  inconvenient  to  wait  for 
a  warm  spell  in  which  to  do  the  work.     To  avoid  removing  all  the  ice, 
filters  have  been  cleaned  one-half  at  a  time.     The  ice  is  removed  from 
one-half  of  the  bed,  the  bed  drained,  and  that  half  cleaned.     Water  is 
then  admitted,  the  remaining  ice  floated  to  the  clean  half  of  the  bed, 
the  bed  drained,  and  the  other  half  cleaned.     At  Hamburg,  filters  have 
been  cleaned  without  draining  by  means  of  a  special  form  of  dredge 
suspended  from  a  scow  and  pulled  back  and  forth  across  the  filter. 
More  recently  a  special  device  has  been  in  use  consisting  of  a  scraper 
and  a  large  pouch  to  hold  the  sand.     The  whole  is  attached  to  a  large 
float  and  is  pulled  back  and  forth  under  the  ice  by  means  of  cables,  it 
being  thus  necessary  to  cut  away  only  a  strip  of  ice  along  each  side. 

530.  Period  of   Service.  —  The   period  of   service  is   the  time  that 
elapses  between  two  scrapings  of  the  filter.     It  may  be  measured  in 
days  or  in  an  equivalent  manner  in  terms  of  amount  of  water  filtered. 
The  period  of  service  depends  upon  the  character  of  the  water,  upon 
the   fineness  of  the  sand,  and  upon  the  maximum  allowable  loss  of 
head.     It   is  directly  affected  by  the  rate,  a  rapidly  working  filter  be- 
coming clogged  proportionally  sooner.     In  practice  it  varies  from  a  few 
days,  if  the  conditions  are  especially  bad,  to  five  or  six  weeks  or  more 
where  the  conditions  are  good.     The  amount  of  water  filtered  between 


EFFECT  OF  SCRAPING  ON  EFFICIENCY  OF  FIL  TRA  TION.        489 


cleanings  ordinarily  ranges  from  40  to  80  million  gallons  per  acre. 
For  many  waters  the  worst  period  is  in  the  algal  season. 

531.  Effect  of  Scraping  on  Efficiency  of  Filtration.  —  In  many  cases 
there  is  a  considerable  decrease  in  the  efficiency  of  a  filter  for  some 
time  after  scraping,  and  in  some  works  it  is  the  practice  to  waste  the 
effluent  for  one  or  more  days  at  this  time.  At  other  places  it  has  been 
found  sufficient  to  begin  the  operation  very  slowly  after  scraping.  This 
method  is  followed  in  a  number  of  the  larger  German  filter-plants.  In 
the  Massachusetts  experiments  there  was,  in  many  cases,  no  deteriora- 
tion of  the  effluent  after  scraping ;  in  others,  such  was  not  the  case. 
As  has  already  been  noted  (Art.  504)  the  effect  of  irregularities  in 
operation,  including  that  of  scraping,  was,  in  these  experiments, 
greatest  with  thin  filters  and  with  coarse  sand.  The  effect  depended 
also  upon  the  depth  of  sand  removed  and  on  the  subsequent  treatment. 
Filling  a  filter  slowly  from  below  was  found  to  give  much  better  results 
than  filling  from  above.  A  good  effect  was  also  observed  if  the  water 
was  permitted  to  stand  a  few  hours  on  the  filter  before  starting  the 
operation.  If  these  precautions  are  followed,  there  is  likely  to 
be  little  need  of  wasting  the  effluent,  but  the  necessity  for  this  in  any 
particular  plant  can  be  readily  determined  by  experience.  When  the 
sand  is  renewed  the  necessity  of  wasting  the  effluent  is  much  greater. 
In  the  operation  of  the  Albany  plant  the  effect  of  scraping  is  very 
small  in  the  warmer  months.  During  the  winter  months;  however,  the 
effect  is  marked.  The  effect  of  the  occasional  refilling  is  also  very 
marked.  Detailed  data  are  given  in  Table  No.  71  A.* 

TABLE   NO.    71A. 

BACTERIAL   RESULTS   FROM  ALBANY  FILTERS    DURING   PERIODS   OF   SCRAPING   AND 
REFILLING,    1899-1903. 


Time. 

256  Scrapings 
during  the 
eight  warmer 
months 
(April  to 
November)  . 

115  Scrapings 
during  the 
four  colder 
months 
(December 
to  March). 

Fourteen 
Refillings. 

"Third  day  before 

68 

Second  day  before 

d.8 

iy4 

C.2 

Last  day  before               .        .... 

62 

**O 

272 

.      68 

First  day  after     . 

OI 

*86 

a.o8 

Second  day  after     

74. 

741 

'<7o 

Third  day  after   

82 

IIOO 

AAA 

Fourth  day  after          . 

OI 

1468 

Fifth  day  after  

82 

I  312 

c86 

Raw  water    

T  4.  COO 

74.8OO 

2  s2OO 

Mixed  effluent      

60 

596 

131 

Average  efficiency  of  whole  plant  for  the  same 
periods  

99.58% 

99.20% 

-    99.48% 

*  Trans.  Am.  Soc.  C.  E.,  1904,  LIII.  p.  247. 


490 


SLOW  SAND  FIL TRA TION. 


532.  Sand- washing.  —  Various  methods  have  been  employed  for 
washing  dirty  sand,  two  of  which  deserve  notice.  The  revolving  drum 
washer,  used  largely  in  Germany,  at  Berlin  and  other  places,  consists 
of  a  large  iron  drum,  slightly  conical  in  form  and  open  at  both  ends. 
The  axis  is  horizontal.  Sand  is  run  in  at  the  large  end,  and  as  the 
drum  revolves  it  is  gradually  moved  towards  the  smaller  and  higher 
end  by  means  of  interior  screw-blades.  Water  enters  at  the  other  end 
and  in  flowing  over  the  sand  thoroughly  cleans  it.  The  amount  of 
water  required  at  Bremen  is  stated  to  be  7  to  8  times  the  amount  of 
sand  washed,*  or  about  1500  gallons  per  cubic  yard  of  sand. 

The  other  form,  known  as  the  ejector  sand- washer,  has  been  in  use 


FIG.  136.  —  PORTABLE  EJECTOR,  WASHINGTON,  D   C. 

in  England  for  many  years.  It  has  also  displaced  the  drum  washer  at 
Hamburg  and  is  now  generally  employed  in  this  country,  both  for 
elevating  and  washing  the  sand.  The  filter  plant  is  fitted  up  with  high- 
pressure  water  mains,  a  3-  or  4-inch  branch  running  to  each  filter.  In 
removing  the  sand  from  a  bed  a  portable  ejector  is  connected  up  with 
the  high-pressure  pipe  line  by  means  of  a  short  line  of  hose.  The  sand 
is  then  shoveled  into  the  ejector  which  forces  it  through  another  line 
of  pipes  to  the  washer.  There  it  is  washed  by  other  sets  of  ejectors  and 
forced  again  through  pipes  to  storage  or  back  at  once  to  one  of  the 

*  For  details  see  Trans.  Am.  Soc.  C.  E.,  1904,  LIII.  p.  227. 


BACTERIAL    CONTROL    OF  FILTER    OPERATIONS. 


491 


niters.      Very  little  manual  labor  is  required  and  the  sand  is  handled 
very  economically. 

The  design  of  ejectors  and  pipe  system  was  very  carefully  worked 
out  at  the  Washington  plant.  Fig.  136  shows  the  portable  ejector 
there  used.  The  sand  is  shoveled  into  the  steel  box,  is  there  lifted  and 
made  liquid  by  water  forced  through  the 
perforated  pipes  near  the  bottom  of  the 
box,  and  is  then  carried  away  by  the 
action  of  the  ejector  jet.  The  mixed  sand 
and  water  is  carried  through  a  4-inch  pipe 
to  the  washer.  Fig.  I36a  shows  the  ejector 
used  for  washing  purposes.  The  sand, 
containing  a  large  proportion  of  water,  is 
discharged  into  the  hopper  from  above,  the 
water  overflowing  the  edge  and  carrying 
away  with  it  the  dirt.  The  clean  sand 
settles  and  is  forced  out  through  the  ejector 
at  the  bottom.  As  the  ejector  tends  to 
carry  out  more  water  than  it  supplies,  some 
of  the  dirty  water  from  above  would  be 
carried  along  with  the  sand  if  no  additional 
water  were  supplied.  To  avoid  this  an 


•Auxiliary  Jef 


FIG.  i36a.  —  EJECTOR  WASHER, 
WASHINGTON,  D.  C. 


auxiliary  supply  is  introduced  near  the  bottom  sufficient  in  amount  to 
prevent  a  downward  current.  By  this  means  a  single  hopper  will  effect 
good  results  although  two  hoppers  are  provided  which  may  be  operated 
in  series.  In  earlier  plants  the  auxiliary  jet  was  not  used,  with  the 
result  that  four  or  five  hoppers  were  required.  A  photograph  of  the 
complete  washing  apparatus  is  shown  in  Fig.  I36b.* 

A  valuable  investigation  was  also  made  at  the  Washington  plant  on 
the  flow  of  mixtures  of  sand  and  water  through  pipes.  It  was  found 
that  velocities  of  from  3  to  4  feet  per  second  were  needed  to  prevent 
stoppage.f 

The  cost  of  cleaning  and  replacing  sand  will  usually  range  from 
$1.00  to  $1.50  per  cubic  yard.  At  Washington  it  .is  estimated  to  cost 
but  40  cents  per  cubic  yard  for  labor.  From  1500  to  2500  gallons  of 
water  are  used  per  cubic  yard  of  sand. 

533.  Bacterial  Control  of  Filter  Operations. — The  most  accurate 
way  in  which  to  control  the  operation  of  filter-plants  is  to  subject  the 
water  to  a  bacterial  examination.  This  should  be  made  at  frequent 

*  See  reference  No.  43,  p.  501,  relative  to  new  method  of  sand  washing. 
t  Trans.  Am.  Soc.  C.  E.,  1906,  LVII.  p.  586. 


492 


SLOW  SAND   FILTRATION. 


intervals  so  as  to  note  any  possible  changes  in  quality.  The  experience 
with  European  filter  systems  has  shown  that  an  impairment  in  quality 
has  not  infrequently  been  detected  in  time  to  prevent  outbreaks  of  dis- 
ease. In  the  larger  filter-plants,  a  bacteriological  laboratory  should  be 
installed,  and  daily  tests  of  the  effluent  made.  The  filter-beds  should 
be  arranged  so  that  the  effluent  from  each  can  be  tested  separately, 
and  provision  made  so  that  the  filtered  water  can  be  rejected  from  any 
one  filter  if  not  up  to  standard.*  In  this  way  a  scientifically  con- 
trolled study  can  be  made  of  all  the  filter  operations  and  optimum  con- 


FIG.  i36b.  —  SAND  WASHER,  WASHINGTON,  D.  C. 

(From  Trans.  Am.  Soc.  C.  E.,  vol.  LVII.) 

ditions  as  to  rate  of  filtration,  cleaning,  filling,  etc.,  determined.  In 
Germany,  compulsory  examination  of  all  sand  filters  is  now  in  force, 
reports  of  the  working  of  the  same  being  sent  to  the  Imperial  Board  of 
Health  at  stated  intervals. 

The  control  of  such  operations  is  a  matter  of  some  importance.  If 
the  examinations  are  conducted  under  the  direct  supervision  of  the 
superintendent  of  works,  it  is  possible  to  more  satisfactorily  study  the 
problems  that  arise  in  connection  with  the  operation  of  the  filters ;  but 
at  the  same  time,  tests  made  by  disinterested  parties,  such  as  Boards  of 
Health,  are  received  with  more  confidence  by  the  public.  The  work, 

*  Koch  traced  the  cholera  outbreak  in  Altona  in  the  winter  of  1893  to  the  im- 
perfect operation  of  one  filter 


PRELIMINARY  TREATMENT  FOR  SLOW  SAND  FILTRATION.     493 

while  requiring  familiarity  with  bacteriological  technique,  is  of  such  a 
character  that  it  can  be  carried  out  under  proper  supervision  by  per- 
sons having  but  limited  experience  in  bacteriological  work. 

Rules  for  Bacterial  Control.  —  The  rules  formulated  in  1898  by  the 
German  Imperial  Board  of  Health  are  still  representative  of  good  prac- 
tice. They  are  in  brief  : 

1.  Each  filter  shall  be  tested  daily.     This  necessitates  an  arrange- 
ment to  secure  samples  from  drains  at  any  time,  a  feature  that  is  now 
regarded  as  essential  for  bacteriological  work,  but  one  which  has  fre- 
quently been  neglected  in  past  construction. 

2.  Rate  of  filtration  must  not  exceed   100  mm.  per  hour  (2.57  mil- 
lion gallons  per  acre  per  day). 

3.  No  filtered  water  should  be  admitted  to  the  mains  that  contains 
more  than  100  bacteria  per  c.c. 

This  quantitative  limit  is  purely  arbitrary,  but  good  filter  practice 
indicates  that  this  is  not  beyond  reach.  Generally  speaking,  the  average 
of  properly  constructed  filters  will  fall  below  this,  although,  as  has  been 
noted  previously,  even  in  the  best-manipulated  filters  there  is  consider- 
able variation  in  germ  content  from  day  to,  day.  An  additional  valuable 
control,  which  is  coming  to  be  frequently  employed,  is  the  test  for  the 
presence  of  B.  coli.  In  testing  filters  as  to  their  efficiency,  samples 
should  be  collected  at  periods  when  the  effluent  is  likely  to  be  the  least 
favorable,  as  during  frost  periods,  heavy  rains,  and  periods  of  greatest 
consumption. 

534.  Preliminary  Treatment  of  Water  for  Slow  Sand  Filtration.  — 
Nearly  all  waters  contain  at  times  suspended  matter  to  such  an  amount, 
or  of  such  a  character  as  to  render  desirable  a  preliminary  treatment 
for  the  removal  of  a  portion  of  this  sediment.     This  may  be  simply  a 
question  of  the  most  economical  method  of  treatment,  or  the  water  may 
be  of  such  character  as  to  render  such  preliminary  treatment  necessary 
for  satisfactory  results.     Large  quantities  of  clay  or  silt  clog  up  a  filter 
quickly,  and  if  the  sediment  is  very  fine  it  penetrates  deeply  into  the 
filter  and  may  make  the  effluent  turbid. 

Preliminary  treatments  may  consist  of  simple  sedimentation,  sedi- 
mentation with  coagulation,  or  preliminary  rapid  filtration  with  or  with- 
out coagulation  and  sedimentation. 

535.  Sedimentation.  —  In  the  filtration  of  river -waters  it  will  nearly 
always  be  economical  to  provide  at  least  a  few  hours'  preliminary  sedi- 
mentation.    This  subject  has  already  been  discussed  in  Art.  466. 

While  river-waters  are  most  subject  to  great  turbidity,  supplies  de- 
rived from  lakes  may  also  give  trouble  from  this  cause.  A  noteworthy 


494  SLOW  SAND  FILTRATION. 

example  is  at  Ashland,  Wis.,  where,  during  the  "break-up"  of  the  ice 
in  the  spring  with  strong  wind  action,  the  bay  from  which  the  water- 
supply  is  derived  is  rendered  so  turbid  as  to  greatly  impair  the'  effi- 
ciency of  the  nitration  process.  Examinations  made  by  Russell  * 
during  such  a  period  showed  only  20  to  30  per  cent  bacterial  efficiency. 
In  some  cases  the  period  of  service  of  the  niters  was  reduced  to  four 
days ;  and  under  such  conditions  the  effluent  was  quite  cloudy.  The 
various  details  connected  with  the  construction  and  operation  of  set- 
tling-basins are  discussed  in  the  preceding  chapter. 

536.  Sedimentation  with  coagulation.  —  The  elaborate  experiments 
at  Cincinnati,  Louisville,  and  New  Orleans,  and  the  accumulated 
experience  in  treating  the  water  of  the  streams  in  the  Mississippi 
Valley,  have  shown  that  nitration  preceded  only  by  plain  sedimenta- 
tion is  inadequate  to  give  satisfactory  results.  Ordinarily  from  30  to 
50  parts  of  suspended  matter  per  million  can  economically  be  taken 
care  of  by  the  niters,  although  it  is  not  the  amount  but  rather  the  nature 
that  determines  whether  a  good  effluent  can  be  secured.  Where  this 
is  not  possible  the  use  of  a  coagulant  is  necessary.  This  should  be 
employed  in  connection  with  settling-basins  as  described  in  Chapter  XX. 
The  construction  and  operation  of  the  niters  is  the  same. 

Experience  in  the  operation  of  the  slow  sand-filter  plant  at  Wash- 
ington, D.  C.,  has  also  shown  that  perfectly  clear  water  cannot  always 
be  secured  even  with  the  long  period  of  sedimentation  there  obtained. 
The  amount  of  the  turbidity  is  not,  however,  sufficiently  great  to  render 
the  use  of  a  coagulant  necessary. 

537.  Preliminary  Filtration.  —  In  purifying  badly  polluted  waters, 
and  especially  those  of  high  turbidity,  some  form  of  rapid  filter  may 
often  be  adopted  to  advantage  for  preliminary  treatment,  slow  sand 
filters  being  employed  for  the  final  process.  In  other  cases  a  prelimi- 
nary filter  may  be  used  for  reasons  of  economy,  the  increased  rate  thus 
permitted  in  the  main  filters  effecting  a  greater  saving  than  the  cost  of 
the  preliminary  treatment. 

At  Albany,  rapid  sand-filters  have  been  adopted  for  preliminary 
treatment  after  a  careful  study  of  the  most  economical  method  of 
enlarging  the  capacity  of  the  present  slow  sand-filter  plant.  A  rate 
of  about  100,000,000  gallons  per  acre  per  day  will  be  used  in  the  rapid 
filters  with  twelve  hours  plain  sedimentation.  This  will  allow  the  slow 
sand-filter  plant  to  be  operated  at  a  rate  of  about  6,000,000  gallons  per  acre 

*  Purification  of  Ashland  Water-supply  by  Sand  Filtration,  i6th  Kept.  Wis.  Bd. 
Health,  1895,  p.  78. 


DOUBLE  FILTRATION. 


495 


per  day,  thus  doubling  its  capacity.  Considerable  saving  in  cost  will 
be  effected  and  a  more  reliable  effluent  secured  than  if  the  present 
plant  were  duplicated. 

At  Philadelphia,  preliminary  filters  are  used  in  some  of  the  plants. 
At  the  Belmont  plant  these  consist  of  rapid  sand- filters  operated  at  a 
rate  of  about  80,000,000  gallons  per  acre  per  day.  At  the  lower 
Roxborough  plant  they  consist  of  so-called  "scrubbers"  designed  by 
Mr.  P.  J.  A.  Maignen  and  described  in  Art.  556  (Chap.  XXIII).  These 
remove  about  60  per  cent  of  the  turbidity  and  75  to  80  per  cent  of  the 
bacteria,  and  enable  the  sand  filters  to  operate  at  a  rate  of  about 
6,000,000  gallons  per  acre  per  day,  with  a  saving  in  cost.  Preliminary 
filters  of  the  Maignen  type  are  also  used  at  South  Bethlehem,  Pa.,  slow 
sand  filters  being  operated  at  a  rate  of  7,000,000  gallons  per  acre  per  day.* 

538.  Double  Filtration.  —  Double,  slow  sand  filtration  is  in  use  in  a 
number  of  European  works,  notably  at  Bremen,  Germany,  Shiedam, 
Holland,  and  Zurich,  Switzerland.  Two  sets  of  sand  filters  are  used, 
operated  in  about  the  same  manner,  although  the  rates  of  filtration  are 
usually  different  in  the  two  sets.  At  Bremen,  this  method  was  adopted 
especially  to  secure  adequate  results  at  times  of  floods  when  the  bac- 
terial content  in  the  raw  water  is  very  high.  A  somewhat  higher  rate 
tfran  the  normal  is  used  in  the  final  filter,  j-  Some  typical  bacterial 
results  secured  during  a  period  of  high  water  are  here  given : 

BACTERIA  PER  CUBIC  CENTIMETER. 


Raw  Water. 

Preliminary  Filter. 

Final  Filter. 

4500 

94 

10 

9600  ' 

96 

9 

29000 

105 

2 

39200 

130 

10 

38300 

52S 

15 

35600 

385 

32 

17200 

165 

35 

7600 

100 

3° 

6400 

75 

13 

This  method  of  double  filtration  should  be  distinguished  from  the 
use  of  rapid  preliminary  filters  as  described  in  the  preceding  article.  It 
is  quite  probable,  however,  that  some  method  of  rapid  filtration  such  as 
used  in  the  United  States  would  prove  more  advantageous  than  the 
method  of  double  sand  filtration  here  described. 


*  Eng.  Record,  1905,  LIT.  p.  61. 

t  Trans.  Am.  Soc.  C.  E.,  1904,  LIII.  p.  210. 


496  SLOW  SAND   FILTRATION. 

539.  Intermittent  Filtration.  —  By  intermittent   filtration    is   meant 
nitration  of  water  through  sand  in  an  intermittent  instead  of  a  contin- 
uous manner,  thus  permitting  the  filter-bed  to  be  exposed  to  the  influ- 
ence of  air  during  the  periods  of  rest.     This  method  is  the  one  used  in 
sewage  filtration  and  is   necessary  in  that  case  because  of  the  large 
amount  of  organic  matter  present.     In  water  purification,  however,  the 
amount  of  unstable  organic  matter  present  is  never  very  large,  and  it  is 
found  by  experience  that  continuous  operation  gives  practically  as  good 
results  as  intermittent  operation.     This  is  due  to  the  fact  that  the  amount 
of  oxygen  dissolved  in  the  water  is  sufficient  for  the  nitrification  process 
without  aeration  of  the  filter-bed. 

A  few  plants  have  been  constructed  to  operate  on  the  intermittent 
plan,  the  most  noteworthy  and  one  of  the  first  plants  built  in  the  United 
States  being  that  at  Lawrence,  Mass.  The  intermittent  plan  was  there 
adopted  because  of  the  excessively  polluted  water  to  be  treated,  it  being 
thought  at  that  time  that  continuous  operation  would  not  give  satisfac- 
tory results.  Besides  the  method  of  operation,  certain  other  special 
features  were  introduced  on  account  of  the  necessity  for  great  economy. 
The  filter  was  composed  of  a  single  bed  of  2\  acres  and  constructed 
without  a  water-tight  bottom.  The  drainage  system  was  made  very 
much  less  extensive  than  in  ordinary  filters,  considerable  lateral  move- 
ment through  the  sand  thus  being  necessary.  The  cost  of  the  filter 
(open)  was  only  $26,000  per  acre. 

On  account  of  the  demand  for  water  the  Lawrence  filter  has  been 
operated  more  generally  as  a  continuous  filter  and  it'  has  been  found 
that  the  results,  both  chemically  and  bacteriologically,  are  practically  the 
same  by  both  methods.  (See  data  in  Art.  489.)*  While  the  first  cost 
was  very  low  the  cost  of  operation  has  been  very  high,  owing  to  the 
lack  of  division  walls  and  the  trouble  from  ice  in  the  winter.  Additional 
filters  built  in  1906  are  of  the  usual  covered  type. 

Following  the  practice  at  Lawrence,  an  intermittent  filter  was  con- 
structed at  Mt.  Vernon,  N.  Y.  This  plant,  like  the  Lawrence  plant,  is 
now,  however,  operated  on  the  continuous  plan.  The  experience  of  these 
cities  and  the  results  of  operation  of  many  continuous  filters  handling 
badly  polluted  water  indicate  that  intermittent  operation  is  more  expen- 
sive and  troublesome  than  continuous  operation  and  that  it  is  rarely  if 
ever  advantageous. 

540.  Cost  of  Filters.  —  The  cost  of  sand  filters  depends  greatly  upon 
local   conditions    as  influencing  cost    of    excavation,   cost  of    sand,  etc. 

*  Trans.  Am.  Soc.  C.  E.,  1901,  XLVI.  pp.  299,  335. 


COST  OF  OPERA  TION.  497 

Large  beds  and  extensive  works  will  cost  less  per  unit  area  than  smaller 
ones,  other  things  being  equal.  At  Berlin,  covered  filters  of  about 
0.6  acre  each  have  cost  about  $70,000  per  acre.  At  Zurich,  filters  of 
i-  acre  each  cost,  for  the  masonry  and  filtering  materials  only,  about 
$48,000  per  acre  for  open  and  $72,000  for  closed  beds.  Engineer 
Lindley  estimates  as  a  reasonable  cost  in  Europe  for  carefully  designed 
filters  about  $68,000  per  acre  for  covered  and  $45,000  for  open  filters. 

At  Ashland,  Wis.,  three  covered  filters  of  \  acre  each  cost  $40,178, 
but  the  engineer  estimated  that  under  normal  conditions  the  cost  there 
would  be  about  $35,000  for  beds  of  \  acre  each,  which  is  equal  to 
$70,000  per  acre.  At  Poughkeepsie  a  single  open  bed  of  29,640  square 
feet  cost  $28,899,  equal  to  $42,000  per  acre.  At  Berwyn,  Pa.,  three 
open  beds  of  7500  square  feet  each  cost  $18,536,  equal  to  $36,000  per 
acre.  At  Albany  the  cost  for  eight  covered  filters  of  an  area  of  0.7 
acre  each  was  $45,600  per  acre,  not  including  land  and  engineering; 
the  latter  item,  figured  pro  rata  from  the  total  cost,  would  add  about 
$2500  per  acre.  The  covers  were  estimated  to  have  added  about 
$13,000  per  acre  to  the  cost.  The  cost  of  covered  filters  at  Washing- 
ton was  $75,000  per  acre,  the  high  cost  compared  to  that  at  Albany 
being  due  to  higher  unit  prices.  To  the  cost  of  filters  will  have  to  be 
added  the  cost  of  clear- water  reservoir,  and  usually  sedimentation-basins, 
amounting  to  from  $3000  to  $10,000  per  million  gallons  capacity 
according  to  the  circumstances. 

541.  Cost  of  Operation. — The  principal  items  in  the  cost  of  opera- 
tion are  the  scraping  of  the  filters,  and  the  cleaning  and  renewal  of  the 
sand.  The  cost  of  scraping  will  ordinarily  range  from  60  cents  to 
$1.20  per  million  gallons  filtered,  although  removal  of  ice  may  greatly 
increase  this.  It  is  stated  to  have  cost  at  London  86  cents  per  million 
gallons;  at  Liverpool,  $1.14;  at  Hudson,  N.  Y.,  88  cents;  and  at 
Poughkeepsie  as  high  as  $2.78,  due  to  ice.  At  Lawrence,  Mass.,  the 
average  cost  of  removal  of  ice  from  1895  to  1900  was  about  $2.27  per 
million  gallons.  The  amount  of  sand  removed  may  be  taken  at  from 
i  to  2  cubic  yards  per  million  gallons  filtered.  The  cost  of  washing  is 
about  30  cents'  per  cubic  yard,  making  the  cost  per  million  gallons  from 
30  to  60  cents.  Then  the  items  of  replacing  the  sand,  repairs,  and 
superintendence  will  bring  the  total  operating  expenses  up  to  from 
$2.00  to  $3.00  per  million  gallons.  At  Poughkeepsie  the  average  cost 
for  twenty  years  has  been  $2.99  per  million. 

At  Washington  the  cost  is  especially  low  due  to  very  economical 
methods  of  sand  handling  and  the  comparatively  long  period  of 
service  possible.  For  the  first  six  months  of  1906  the  average  cost  for 


498  SLOW  SAND  FILTRATION*. 

cleaning  and  for  office  and  laboratory  expenses  is  given  as  about  $1.25 
per  million  gallons.  At  the  upper  Roxborough  niters  of  the  Philadelphia 
plant  the  cost  for  1903  was  $0.95  for  scraping  and  washing  per  million 
gallons  filtered. 

The  cost  of  operation  at  Albany,  including  superintendence,  from 
July  26,  1899,  to  July  i,  1900,  is  given  as  follows :  * 

Av.  Cost  per  1,000,000  Gals. 

Scraping $0.25 

Wheeling  out  sand / 50 

Washing  sand 


water 05 

Refilling    39 

Cleaning  sedimentation  basin 06 

Incidentals 20 

Total $1.99 

Laboratory  expenses $0.34 

The  total  cost  of  filtration,  including  interest  and  depreciation, 
may,  under  ordinary  circumstances,  be  estimated  at  from  $7.00  to 
$9.00  per  million  gallons  filtered. 

LITERATURE. 

(See  also  Chapter  XIX.) 

ARTICLES    OF    A   GENERAL   CHARACTER. 

1.  Kirkwood.     Filtration    of  River-waters.     New  York,  1869. 

2.  Frankland.     Water    Purification ;    its    Biological    and    Chemical    Basis. 

Proc.  Inst.  C.  E.,  1885-86,  LXXXV.  p.  197. 

3 .  Bertschinger.     Experiments  at  Zurich  on  the  Influence  of  Rate,  Scraping, 

etc.     Jour.  f.  Gas.  u.  Wasservers.,  1889,  1891. 

4.  Drown.     Filtration    of    Natural  Waters.     Jour.    Assn.  Eng.   Soc.,   1890, 

ix.  p.  356. 

5.  Massachusetts    Board    of    Health.     Special    Report,  1890,  and    Annual 

Reports  since,  contain  results  of  the  very  valuable  experiments  of 
the  Lawrence  Experiment  Station. 

6.  Piefke.       Neue    Ermittelungen   iiber    Sand  filtration.     Jour.    f.    Gas.    u. 

Wasservers.,  1891,  xxxiv.  p.  208. 

7.  Sedgwick.     The  Purification  of    Drinking-water  by  Sand  Filtration ;  Its 

Theory,  Practice,  and  Results ;  with  Special  Reference  to  American 
Needs  and  European  Experience.  Jour.  New  Eng.  W.  W.  Assn., 
1892,  vii.  p.  103. 

8.  Frankland.     The  Micro-organisms  in  Water.     London,  1894. 

9.  Kiimmel.     Versuche    und  Bebbachtungen  iiber  die  Wirkung  von  Sand- 

filtern.     Jour.  f.  Gas.  u.  Wasservers.,  1893,  xxxvi.  p.  161. 


*  Eng.  News,  1900,  XLIV.  p.  88. 


LITER  A  TURK. 


499 


10.  Mills.     Purification    of   Sewage    and    Water  by  Filtration.     Trans.  Am. 

Soc.  C.  K,  1893,  xxx.  p.  350. 

11.  Kiimmel.     Some  Questions  concerning  the  Filtration  of  Water.     Trans. 

Am.  Soc.  C.  K,  1893,  xxx.  p.  330. 

12.  Koch.     Wasserfiltration  und  Cholera.     Zeit.  f.  Hyg.,  xiv.  p.  393. 

13.  Piefke.     Ueber  die  Betriebsfuhrung  von  Sandfiltern.     Zeit.  f.  Hyg.,  1894, 

xvi.  p.  151. 

14.  Fuertes.     Some  of  the  Factors  which  Determine  the  Efficiency  of  Filters 

for  Water  Purification.  Eng.  Record,  1896,  xxxiv.  p.  160. 
Describes  several  regulating  devices. 

15.  Hazen.      Mechanical    Analysis    of    Filtering    Materials.      Eng.    Record, 

1897,  xxxv.  p.  163. 

1 6.  Magar.     Reinigungsbetrieb  der  offener  Sandfilter  des  Hamburger  Filter- 

werkes  in  Frostzeiten.  Jour.  f.  Gas.  u.  Wasservers.,  1897^.4; 
Eng.  Record,  1897,  xxxv.  p.  471.  Describes  device  for  cleaning 
filter-beds  under  the  ice. 

17.  Pannwitz.     Die  Filtration  von  Oberflachenwasser  in  den  deutschen  Was- 

serwerken  wahrend  der  Jahre  1894-1896.  Contains  many  full  and 
valuable  data.  Arb.  a.  d.  Kais.  Gesundheitsamte,  1898,  xiv.  p.  153. 

1 8.  Kenna.     The  Biology  of  Sand  Filtration.     Read  before  the  Annual  Con- 

vention of  the  British  Association  of  Water-works  Engineers. 
Abstract  in  Eng.  News,  1899,  XLI-  P-  4J9-  A  study  of  the  organ- 
isms of  the  sediment-layer  of  niters. 

19.  Gotze.     Doppelte  Sandfiltration  fur  Centrale  Wasserversorgung.     Arch. 

f.  Hyg.,  xxxv.  p.  237. 

20.  Gregory.     Economical    Dimensions    of    Rectangular    Filter  Beds.     Eng. 

News,  1900,  XLIV.  p.  252. 

21.  Beer.     Die  Arbeiten  der  Commission  deutscher  und  auslandischer  Filtra- 

tions-Techniker  und  Erfahrungen  uber  Sandfiltration.  A  valuable 
review  of  filtration  in  Germany.  Jour.  f.  Gas.  u.  Wasservers.,  1900, 
XLIII.  p.  589.  Abs.  Eng.  Record,  1900,  XLII.  p.  416. 

22.  Hazen.     Covering   Water    Filters.     Report    on  Trenton  Water    Supply. 

Eng.  Record,  1901,  XLIII.  p.  276;  Eng.  News,  1901,  XLV.  p.  58. 

23.  Fuertes.       Notes    on    Designing   and    Constructing    Slow    Sand    Filters. 

Eng.  Record,  1901,  XLIII.  p.  79. 

24.  Gregory.     On  the  Design  and  Construction  of  Slow  Sand  Filters.     Eng. 

Record,  1903,  XLVTI.  p.  663. 

25.  Anthony.     Automatic  Modules  for  Regulating  the    Speed  of   Filtration. 

Trans.  Am.  Soc.  C.  E.,  1903,  LI.  p.  136. 


ARTICLES    RELATING    TO    SPECIFIC    WORKS. 

1.  Halbertsma.     Filteranlagen  in  den  Niederlanden.     Jour.  f.  Gas.  u.  Was- 

servers., 1892,  xxxv.  p.  43. 

2.  Preller.     Water-supply,  Power,  and  Electric   Works    of   Zurich,    Switzer- 

land.    Proc.  Inst.  C.  E.,  1892-93,0x1.  p.  257. 

3.  Fowler.     The    Filter-beds    at   Poughkeepsie,  N.  Y.     Eng.  News,   1892, 

xxvn.  p.  432. 

4.  Mills.     The  Filter  of  the  Water-supply  of  the  City  of  Lawrence  and  its 

Results.     Report  Mass.  Board  of  Health,   1893,  p.  543  ;  Jour.   New 
Eng.  W.  W.  Assn.,  1894,  ix.  p.  44. 


5 00  SLOW  SA ND  FIL TRA TION. 

5.  Sand  Filtration  at  Hudson,  N.  Y.     Eng.  News,  1894,  xxxi.  p.  487. 

6.  Aeration  and  Continuous  Sand   Filtration  at  Ilion,  N.  Y.     Eng.  News, 

1894,  xxxi.  p.  466. 

7.  Aeration    and    Intermittent    Sand    Filtration    at    Mount   Vernon,    N.  Y. 

Eng.  News,  1894,  xxxn.  p.  155. 

8.  Meyer.     Das  Wasserwerks  Hamburgs.     Hamburg,  1894. 

9.  Gill.     The   Filtration  of   the  Miiggel  Lake  Water-supply,  Berlin.     Proc. 

Inst.  C.  E.,  1894-95,  cxix.  p.  236. 

10.  Grahn.     Wasserreinigung  und  Filtration  fur  die  Wasserwerksanlage  der 

Stadt    Magdeburg.       Jour.    f.    Gas.    u.    Wasservers.,   1895,  xxxvm. 
p.  85. 

11.  Halbertsma.     Die    Resultate     der     doppelten    Filtration    zu    Schiedam. 

Jour.  f.  Gas.  u.  Wasservers.,  1896,  xxxix.  p.  467. 

12.  Wheeler.       Masonry-covered    Sand    Filter-beds    at    Ashland,    Wis.  Jour. 

New    Eng.    W.    W.    Assn.,  1897,    xi.    p.    301  ;    Eng.   News.  1897, 
xxxvin.  p.  338. 

13.  Fowler.     Slow  Sand  Filtration  at  Poughkeepsie,  N.  Y.     Jour.  New  Eng. 

W.  W.  Assn.,  1898,  xii.  p.  209. 

14.  Fuertes.     Water    Filtration,    Zurich,    Switzerland.       Eng.    Record,   1899, 

xxxix.  p.  472. 

15.  Recent   Experience   with   the   Lawrence    Filter.     Eng.  Record,  1899,  XL. 

p.  597.     Describes   trouble   with  clogging   by  iron  and    crenothrix, 
and  method  of  cleaning. 

1 6.  Kiersted.     Water-supply  and  Purification  Works  at  Parkville  and  Bethany, 

Mo.       Sedimentation     and    Filtration.       Eng.    News,    1899,    XLII. 
p.  388. 

17.  Hazen.     The  Albany  Filtration  Plant.       Trans.  Am.  Soc.  C.  E.,  1900, 

XLIII.  p,  244. 

1 8.  The  Lower  Roxborough  Filter  Plant  at  Philadelphia.     Eng.  Record,  1900, 

XLII.  p.  532. 

19.  The  Upper  Roxboroagh  Filter  Plant  at  Philadelphia.     Eng.  Record,  1901, 

XLIII.  p.  341. 

20.  Six  Years  of  Slow  Sand  Water  Filtration  at  Mount  Vernon,  N.  Y.     Eng. 

News,  1901,  XLV.  p.  394. 

21.  Houston.     The    Construction  of   Gravity    Sand  Filters  at  Nyack,  N.  Y. 

Trans.  Am.  Soc.  C.  E.,  1901,  XLV.  p.  476. 

22.  Knowles  and    Hyde.     The  Lawrence,  Mass.,  City  Filter:  A  History  of 

Its    Installation   and   Maintenance.      Trans.  Am.  Soc.  C.  E.,  1901, 
XLVI.  p.  258. 

23.  The   Pittsburg  Water    Purification  Works.     Eng.  Record,  1902,  XLV.  p. 

73  ;  Eng.  News,  1902,  XLVI.  p.  137. 

24.  The  Antietam  Filters  of  the  Reading  Water  Works.     Eng.  Record,  1905, 

LI.  p.  340.     The  Egelman  Plant  of  same  City.     Eng.  Record,  1903, 
XL vin.  p.  566. 

25.  Sand   Washers    at   the    Roxborough  Filters.     Eng.  Record,  1903,  XLVIII. 

p.  426. 

26.  The  Philadelphia  Filtration  System.     Eng.  News,  1904,  LII.  p.  144. 

27.  Hill.     The    Belmont   Filtration    Works,    Philadelphia.     Jour.  Fr.    Inst,, 

1904,  CLI.  p.   I. 

28.  A    Concrete-Steel-Construction    Filtration    Plant    for    the    New   Haven 

Water  Co.     Eng.  Record,  1904,  XLIX.  p.  270. 


LITER  A  TV  RE.  5  O I 

29.  The  Open  Sand  Filters  for  the  Providence  Water-works.     Eng.  Record, 

1904,  L.  p.  356. 

30.  Open  Slow  Sand  Filters  at  Yonkers,  N.  Y.     Eng.  Record,  1904,  L.  p.  31. 

31.  Goetze.     Double  Filtration    at    Bremen.     Trans.  Am.   Soc.  C.  E.,  1904, 

LIII.  p.  210. 

32.  Hill.     The  Management  of  the  Roxborough  Water  Filters,  Philadelphia. 

Eng.  Record,  1905,  LI.  p.  702. 

33.  The  Revised  Plans  for  the  Purification  of  the  Pittsburg   Water-supply. 

Eng.  Record,  1905,  LI.  p.  133,  also  1906,  LIV.  p.  622. 

34.  The    Reconstruction  of   the  Poughkeepsie  Water  Filters.     Eng.  Record, 

1905,  LII.  p.  618. 

35.  A  Reinforced  Concrete  Filtration  Plant  at  Marietta,  Ohio.     Eng.  Record, 

1905,  LI.  p.  452. 

36.  Water   Purification   at    South   Bethlehem,  Pa.      Eng.  Record,  1905,  LII. 

p.  61. 

37.  Mabee.      Reinforced    Concrete    Filter   Bed    Walls    and    Roofs,   Indian- 

apolis, Ind.     Eng.  News,  1906,  LV.  p.  456. 

38.  Swan.     Contractors'    Plant   and    Methods    of  the    Construction    of   the 

Pittsburg  Filtration  Plant.     Eng.  News,  1906,  LVI.  p.  566. 

39.  Hazen  and  Hardy.    Works  for  the  Purification  of  the  Water-supply  of 

Washington,  D.  C.     Trans.  Am.  Soc.  C.  E.,  1906,  LVII.  p.  307. 

40.  The  Water  Filter  of  the  Jacob  Tome  Institute.     Eng.  Record,  1906,  LIV. 

P-  572. 

41.  A  Slow  Sand  Filtration  Plant  and  other  Water-works  Improvements  at 

Denver.     Eng.  Record,  1907,  LV.  p.  740. 

42.  Report  on  the   Filtration  of  the  Croton  Water-supply,  New  York   City. 

Abstract,  Eng.  News,   1907,  LVIII.  p.  561,  Eng.  Record,  1907,' LVI. 
p.  561. 

43.  Fuller.     High    Relative    Rates    of    Filtration    with    Slow    Sand    Filters. 

Describes  Blaisdell  Sand  Washing  Machine.     Eng.  News,  1908,  LIX. 
p.  287. 


CHAPTER   XXII. 
RAPID    SAND    FILTRATION. 

542.  General  Description  of  the  Rapid  Sand  Filter.  —  This  type  of 
filter,  also  called  the  "mechanical  filter"  and  the  "American  filter,"  is 
a  form  of  filter  designed  to  accomplish  results  in  the  way  of  purification 
comparable  with  those  obtained  by  the  slow  sand  filter  already  discussed, 
but  with  a  much  smaller  sand  area.  It  is  similar  to  the  slow  sand  filter 
in  that  the  filtering  material  consists  of  a  bed  of  three  or  four  feet  of 
sand  or  crushed  quartz,  but  in  other  respects  the  construction  and 
operation  are  widely  different.  The  essential  points  of  difference  are : 
the  very  rapid  rate  of  filtration  (100  to  125  million  gallons  per  acre  per 
day),  the  use  of  a  coagulant  to  aid  in  filtration  and  the  manner  of  wash- 
ing the  sand  bed.  These  peculiarities  lead  to  noteworthy  differences  in 
construction.  The  units  are  relatively  small  in  area,  the  coagulating 
basin  becomes  an  essential  part  of  the  plant  together  with  adequate 
means  for  mixing  and  regulating  the  coagulant,  and  the  washing  of  the 
sand,  which,  in  this  type,  must  be  done  every  few  hours,  requires  the 
use  of  special  devices  of  a  more  or  less  elaborate  character.  In 
the  operation  of  a  rapid  filter  plant,  the  frequent  attention  required  of 
each  unit  renders  the  question  of  compact  and  convenient  arrange- 
ment of  piping  and  operating  valves  of  much  importance.  At  the 
same  time  the  small  size  of  the  unit  enables  this  to  be  readily  done, 
and  a  part  of  all  the  plant  to  be  placed  under  roof.  The  washing  of  the 
sand  beds  is  accomplished  by  a  reverse  flow  of  water,  assisted,  usually, 
by  agitation  of  the  sand  bed  by  means  of  mechanical  rakes  or  com- 
pressed air.  The  details  relating  to  this  part  of  the  process  constitute 
the  chief  differences  between  the  various  types  of  rapid  filters. 

The  development  of  the  rapid  filter  arose  from  the  effort  to  settle 
and  clarify  very  turbid  water  by  the  use  of  a  coagulant,  followed  by 
rapid  filtration.  Various  devices  used  in  construction  and  operation, 
such  as  sand  agitators,  supporting  screens,  coagulant  regulators,  as  well 
as  certain  combinations  of  processes  and  parts,  were  patented,  and  for 
several  years  this  type  of  filter  was  almost  exclusively  constructed  by 
various  filter  companies,  being  built  and  sold  in  the  form  of  complete 
units  of  wood  or  steel.  When  bacterial  purification  became  of  greater 

502 


TYPES  OF  CONSTRUCTION.  503 

importance  the  rapid  filter  was  looked  upon  with  much  suspicion,  owing 
to  the  extremely  high  rate  of  filtration  used  as  compared  to  the  rate 
employed  in  the  better  known  slow  sand  filter.  Results  of  daily  opera- 
tion in  practice,  and  of  many  special  experiments  have  shown,  however, 
that  with  proper  supervision  the  rapid  filter  will  give  essentially  the 
same  results  as  the  slow  filter,  and  that  in  some  waters  the  results  are 
better  than  can  be  obtained  by  the  slow  filter  without  the  use  of  a  coag- 
ulant. This  condition  has  led  to  the  quite  general  use,  in  the  United 
States,  of  the  rapid  filter  whenever  it  is  the  better  adapted  to  local 
conditions.  The  extent  of  the  present  use  of  this  type  of  filter,  as 
given  in  Art.  460,  is  sufficient  evidence  of  its  importance  as  an  efficient 
means  of  purification.  While  many  of  the  patented  devices  are  excel- 
lent, their  use  is  not  essential  and  several  very  large  plants  have  been 
constructed  since  1900  by  well  known  engineers  in  which  no  such 
device  has  been  employed. 

The  name  "mechanical  filter"  has,  perhaps,  been  used  to  designate 
this  type  of  filter  more  commonly  than  any  other,  it  having  been  applied 
at  first  largely  because  of  the  mechanical  means  used  in  cleaning  the 
sand  and  the  manner  in  which  complete  units  were  made  up  and  sold. 
Inasmuch,  however,  as  the  fundamental  distinction  between  this  type 
of  filter  and  the  slow  sand  filter  relates  to  the  rate  of  filtration,  with 
the  accompanying  use  of  a  coagulant  and  special  means  of  washing,  and 
as  the  modern  plants  are  now  usually  being  constructed  of  concrete 
without  mechanical  agitators,  it  would  seem  that  the  term  "rapid  filter" 
or  "  rapid  sand  filter "  is  more  suitable.  It  will  hereafter  be  the  one 
employed  in  this  work.  The  term  "American  filter"  has  also  been 
used  to  some  extent,  the  slow  sand  filter  being  called  the  "English 
filter"  in  consideration  of  the  places  where  the  respective  types 
originated. 

543.  Types  of  Construction.  —  The  usual  form  of  rapid  filter,  as 
constructed  and  sold  by  the  proprietary  companies,  consists  of  units 
made  up  of  circular  wooden  or  steel  tanks.  These  contain  the  sand, 
supported  on  suitable  strainers,  and  each  -  is  equipped  with  piping 
arrangements  for  washing  and  means  for  agitating  the  sand.  In  one 
of  the  most  common  designs  formerly  employed  each  tank  was  divided  by 
a  horizontal  partition,  the  lower  portion  acting  as  a  coagulating  chamber. 
The  coagulating  basins  are  now  usually  built  separate  from  the  filters 
so  as  to  provide  larger  settling  capacity.  The  form  of  construction  here 
described  is  illustrated  in  Fig.  137,  which  shows  one  of  the  filters 
installed  at  Chester,  Pa.,  in  1903.  The  filter  unit  consists  of  a  cypress 
tank  15  feet  in  diameter  containing  a  sand  bed  2j  feet  thick.  This  is 


504 


RAPID   SAND  FILTRATION. 


supported  on  a  layer  of  gravel,  near  the  bottom  of  which  are  numerous 
brass  "strainer-heads"  through  which  the  filtered  water  passes  into  a 
system  of  wrought-iron  collecting  pipes.  These  pipes  are  connected  to 
a  large,  central,  cast-iron  collector  which  passes  through  the  tank  and 
joins  the  effluent  pipe  outside.  When  the  sand  is  to  be  washed,  water 


,  Vpper  Wast* 


Wooden  Shelf 
Separating  upper 
part-  of  Trough  froitf 

lowzr 


FIG.  137.  WARREN  "FILTER  AT  CHESTER,  PA. 

(Jfrom  Engineering  Record,  vol.  XLIX.) 

is  forced  backwards  through  the  strainers,  and  at  the  same  time  the  sand 
is  stirred  up  to  its  full  depth  by  means  of  long  iron  fingers  reaching 
into  the  sand  and  which  are  attached  to  a  transverse  arm  mounted  on  a 
vertical  shaft,  the  whole  being  rotated  by  means  of  suitable  gearing. 
The  agitation  and  upward  flow  of  water  thoroughly  cleans  the  sand  in  a 
few  minutes  The  waste  water  escapes  into  a  circular  trough  supported 


TYPES   OF  CONSTRUCTION. 


505 


around  the  inner  edge  of  the  tank,  and  thence  passes  to  a  waste  pipe. 
In  this  particular  form,  a  lower  waste  is  also  provided  to  assist  in  wash- 
ing the  surface  of  the  filter  by  surface  agitation  and  drainage  from  the 
top,  but  without  reverse  flow.  Suitable  regulating  valves  are  provided 
to  maintain  a  constant  level  of  water  on  the  filter  and  a  uniform  rate  of 
filtration.  Each  strainer  consists  of  a  perforated  bronze  plate  attached 
to  a  cylindrical-shaped  strainer-head.  These  strainer-heads  are  screwed 
into  the  branch  pipes  which  form  the  manifold  system.  Further  details 
of  strainers  are  illustrated  in  Art.  550^. 

Instead   of   mechanical  agitators,  compressed   air  may  be  used  for 


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FIG.   138.     FILTER   UNIT,    LITTLE    FALLS,   N.  J. 

(From  Engineering  Record t  vol.  XLIII.) 

agitating  the  sand,  the  air  being  forced  through  the  strainers  alter- 
nately with  the  wash  water.  Mechanical  agitators  of  the  type  illus- 
trated require  the  use  of  circular  tanks,  while  compressed  air  is  readily 
adapted  to  any  form.  In  another  form  of  commercial  filter  the  entire 
bed  is  enclosed  in  a  cylindrical  steel  tank  and  is  operated  under  pres- 
sure. It  is  called  the  "pressure "  filter.  Compressed  air  is  used  to 
agitate  the  sand.  This  type  is  now  seldom  used  as  it  is  not  as  satis- 
factory as  the  open  gravity  type. 

In  many  of  the  modern  plants,  especially  those  of  large  size,  the 
tanks   are  made  of   concrete,  usually  rectangular   in  form,  mechanical 


506  RAPID   SAND   FILTRATION. 

agitation  not  generally  being  employed.  In  this,  case  the  special 
devices  usually  include  only  the  strainer  system  and  the  controllers  ; 
and  several  plants  have  been  built  where  these  parts  have  been  fur- 
nished by  special  manufacturing  companies,  other  portions  of  the  plant 
being  designed  and  constructed  independently.  Fig.  138  illustrates 
this  form  of  construction.  It  represents  one  of  the  units  of  the  plant  at 
Little  Falls,  N.  J.,  the  complete  plant  consisting  of  thirty-two  of  these 
units.  As  shown,  the  tank  is  made  of  reinforced  concrete  and  par- 
tially covered  with  the  same  material.  The  strainer  system  is,  in 
general,  quite  similar  to  that  shown  in  Fig.  137  excepting  as  to  the 
rectangular  arrangement.  Compressed  air  is  used  for  agitating  the 
sand.  During  the  washing  process  the  dirty  water  is  carried  off 
by  means  of  steel  troughs  leading  to  a  gutter  and  thence  to  a  waste 
pipe.  The  convenient  arrangement  of  piping  is  an  important  part 
of  the  design  of  such  plants ;  this  feature  is  discussed  in  Art. 

549  £•• 

544,  Principles  of  Operation.  —  The  action  of  rapid  sand  filters  is 
somewhat  unlike  that  of  slow  sand  niters,  although  the  results  are  not 
greatly  different.  The  effect  of  a  coagulant  in  gathering  the  sediment 
into  relatively  large  masses  has  been  explained  in  Chapter  XX.  It 
aids  nitration  in  this  way,  and  also  forms  a  substitute  for  the  organic 
coating  on  the  sand  grains  and  on  the  surface  of  the  ordinary  sand 
filter.  It  is  the  use  of  a  coagulant  which  enables  such  high  velocities 
to  be  employed.  To  avoid  too  frequent  washing,  it  is  common  to 
employ  heads  as  high  as  10  or  12  feet,  but  with  such  high  heads 
and  velocities  the  sand  becomes  clogged  to  a  considerable  depth. 
The  methods  of  washing,  however,  enable  this  sediment  to  be 
readily  removed.  The  interval  between  washings,  i.e.,  the  "run,"  is 
24  hours  or  less,  and  the  operation  of  washing  requires  from  10  to 
15  minutes. 

In  the  design  of  a  rapid  filter  plant  the  preliminary  treatment  of 
the  water  is  often  a  question  of  much  importance  if  the  most  efficient 
methods  are  to  be  used.  Very  turbid  waters  can  often  best  be  handled 
by  permitting  a  considerable  period  of  subsidence  in  large  basins,  fol- 
lowed by  coagulation  with  a  further  short  period  of  settling ;  others 
may  require  the  use  of  a  coagulant  at  both  periods.  Many  waters  not 
too  turbid  can  be  handled  by  a  single  brief  period  of  sedimentation 
accompanied  by  coagulation.  For  effective  filtration  complete  clari- 
fication is  not  desirable  as  the  flocculent  precipitate  is  necessary  to 
secure  good  results  in  the  filter.  In  many  of  the  early  plants  the 
regulation  of  the  rate  of  filtration  and  the  quantity  of  chemical  applied 


EXPERIMENTS  ON  RAPID   FILTERS.  507 

was  very  poorly  done,  but  in  the  later  designs  very  efficiert  devices 
have  been  introduced  to  accomplish  these  objects.  In  the  removal  of 
color  the  rapid  filter  is  advantageous  because  of  the  accompanying  use 
of  a  coagulant.  Brown  and  peaty  waters  are  quite  markedly  improved 
in  the  process, 

545.  Experiments  on  Rapid  Filters  and  Results  of  Operation.  —  Im- 
portant experiments  on  rapid  filters  have  been  carried  out  at  Provi- 
dence in  1893-4  by  Mr.  E.  B.  Weston ;  at  Louisville  and  Cincinnati 
by  Mr.  George  W.  Fuller  in  1895-6  and  in  1898  respectively;  at 
Pittsburg  in  1897  by  Mr.  Allen  Hazen  ;  at  Washington  in  1899  by 
Col.  A.  M.  Miller;  and  at  New  Orleans  in  1901  by  Mr.  R.  S.  Weston. 
Each  of  these  series  extended  over  a  considerable  length  of  time 
and  was  very  carefully  conducted.  Several  shorter  series  of  analyses 
from  plants  in  regular  operation  are  available  and  give  valuable 
information. 

The  Providence  experiments  were  conducted  on  a  small  experi- 
mental Morison  filter,  The  results  were  of  a  rather  varying  character, 
but  when  the  filter  was  considered  to  be  under  normal  conditions  the 
removal  of  bacteria  was  from  95  to  99.9  per  cent,  averaging  about  98  £ 
per  cent.  The  number  in  the  original  water  was  usually  from  3000  to 
10,000  per  cubic  centimeter.  The  rate  of  filtration  was  128  million 
gallons  per  acre  per  day.* 

(a)  The  Louisville  Experiments.^ —  These  experiments  were  under- 
taken to  determine  the  efficiency  of  rapid  filters  in  the  purification 
of  the  Ohio  River  water.  Besides  important  results  as  to  bacterial 
efficiency,  much  of  value  was  derived  in  regard  to  features  of  construc- 
tion and  operation.  Unusual  difficulties  attended  the  operation  at  this 
place  on  account  of  the  great  amount  of  sediment  carried  at  times,  its 
greatly  varying  character,  and  the  fact  that  the  water  did  not  undergo 
a  preliminary  subsidence. 

With  regard  to  the  qualitative  results,  the  turbidity  was  practically 
all  removed  and  also  a  part  of  the  dissolved  organic  matter.  The 
bacterial  efficiency  was  irregular,  but  when  the  filters  were  operated 
normally  the  efficiency  averaged  from  97^-  to  98^  per  cent  in  the 
various  systems  experimented  with. 

The  greatest  fault  of  all  filters  was  the  lack  of  adequate  settling- 
tanks,  the  capacity  of  those  used  permitting  only  from  20  to  60 
minutes  of  subsidence  as  a  maximum.  In  no  case  did  the  filters  give 


*  Report  of  the  Rhode  Island  State  Board  of  Health,  1894. 
t  Fuller.     Water  Purification  at  Louisville.     New  York,  1898. 


508  RAPID   SAND   FILTRATION-. 

results  satisfactory  from  the  standpoint  of  economy  and  efficiency, 
chiefly  because  of  the  lack  of  a  previous  settling  of  the  water ;  and  such 
subsidence  for  a  day  or  more  is  regarded  as  imperative  in  the  treatment 
of  this  water.  With  such  subsidence,  however,  it  was  estimated  that 
the  average  amount  of  coagulant  (sulfate  of  alumina)  would  be  about 
1.75  grains  per  gallon,  and  with  proper  attention  to  the  operation  it 
was  considered  that  the  result  would  be  thoroughly  satisfactory  under 
all  ordinary  conditions. 

Mr.  Fuller  considered  it  desirable  to  employ  a  layer  of  sand  at  least 
30  inches  in  thickness  and  of  an  effective  size  of  0.35  mm.,  in  order  to 
increase  somewhat  the  frictional  resistance  over  that  offered  by  the 
sand  used,  which  was  from  0.43  to  0.51  mm.  in  diameter.  The  per- 
missible rate  was  considered  to  be  100  million  gallons  per  acre,  or 
over,  and  the  maximum  loss  of  head  about  10  feet.  In  washing  it 
was  observed  that  agitators  were  of  much  help,  and  if  the  washing  was 
thoroughly  done  no  deterioration  of  the  effluent  was  noticeable  on  the 
renewal  of  operations. 

(b)  The  Cincinnati  Experiments*  —  These  experiments  were 
undertaken  primarily  to  determine  the  applicability  of  slow  sand 
filters,  and  this  phase  of  the  subject  has  already  been  discussed  in 
Art.  536.  At  the  same  time  a  rapid  filter  of  the  Jewell  type  was 
experimented  with,  using  water  which  had  undergone  plain  subsidence. 
The  character  of  the  water  is  similar  to  that  at  Louisville.  The 
general  result  as  to  efficiency  was  the  removal  of  an  average  of  98^ 
per  cent  of  the  bacteria,  the  original  number  averaging  about  27,000. 
Excluding  results  obtained  at  the  time  when  certain  changes  were 
being  made  in  the  sand,  the  efficiency  was  99.4  per  cent,  with  an 
average  application  of  1.25  grains  of  sulfate  of  alumina  per  gallon. 
Mr.  Fuller  considered  that  with  about  one-third  of  a  grain  in  addition, 
"the  bacterial  results  would  be  as  good  as  is  practicable  to  obtain  by 
any  method  now  known  ;  that  is  to  say,  the  bacteria  in  the  effluent 
would  average  less  than  100  per  cubic  centimeter,  and  the  average 
annual  removal  of  the  river-water  bacteria  from  present  evidence  would 
amount  to  fully  99^  per  cent."  This  is  a  considerably  higher  efficiency 
than  obtained  at  Louisville,  but  in  the  latter  case  no  preliminary  sub- 
sidence was  allowed. 

Regarding  the  relative  advantages  of  rapid  filters,  and  slow  sand 
filters  with  the  use  of  a  coagulant,  Mr.  Fuller  considers  that  the  former 
"  would  be  the  less  difficult  to  operate,  would  be  somewhat  cheaper, 

*  Fuller.     Report  on  Water  Purification.     Cincinnati,  1899. 


EXPERIMENTS   ON  RAPID   FILTERS.  509 

and  would  give  substantially  the  same  satisfactory  quality  of  filtered 
water,  and  could  be  much  more  readily  and  cheaply  enlarged  for  future 
requirement." 

Other  points  of  value  deduced  from  these  experiments  were,  that  the 
maximum  loss  of  head  should  be  10  or  12  feet,  that  the  rate  could  be 
125  million  gallons  or  perhaps  more,  and  that  provision  for  at  least  6 
hours'  flow  should  be  made  for  coagulation  and  subsidence  immediately 
previous  to  filtration. 

(c)  The  Pittsburg  Experiments*  —  These  experiments  were  made 
on  two  experimental  slow   sand   filters,   one  Jewell  and  one  Warren 
rapid  filter,   and   a   set  of  artificial-stone  tiles  of   the  Fischer  system 
(see  Art.  554).     The  average  bacterial  results  for  seven  months  were 
as  follows : 

Bacteria  Efficiency 

per  c.c.  per  cent. 

River  water n>337 

Effluent  from  Warren  filter 201 1  98.2 

Effluent  from  Jewell  filter    293!  97.2 

Settling-basin  for  slow  sand  filters    9*224 

Effluent  from  slow  sand  filter  No.  i 106  99.1 

"          "        "        "         "        "2 148  98.7 

Sand  filter  No.  2  was  operated  for  four  months  with  unsettled  water, 
otherwise  the  water  for  the  slow  sand  filters  was  given  from  1 2  to  24 
hours'  subsidence.  The  rapid  filters  were  operated  without  preliminary 
subsidence.  The  efficiencies  obtained  throughout  the  tests  were  in 
general  very  uniform,  but  a  lessened  efficiency  frequently  followed,  for 
a  short  time,  the  washing  of  the  rapid  filters.  The  amount  of  coagu- 
lant was  found  to  be  of  vital  importance,  and  up  to  I  grain  per  gallon 
the  efficiency  increased  rapidly  with  the  coagulant.  With  no  coagulant 
it  was  only  50  or  60  per  cent. 

(d)  The  Washington  Experiments.  — The  city  of  Washington  is  sup- 
plied with  a  water  which  is  turbid  for  a  large  portion  of  the  year,  in 
spite  of  the  fact  that  it  passes  through  two  large  reservoirs.     The  effect 
of  storage  is,  in  fact,  greater  upon  the  bacteria  than  upon  the  clay. 
Experiments  were  made  upon  a  slow  filter,  and  upon  a  rapid  filter  using 
a  coagulant.     The  results  were,  in  general,  better  from  the  rapid  filter 
than  from  the  slow  sand  filter,  although  neither  gave  at  all  times  a  clear 
effluent.     The  rapid  type  of  filter  was  recommended   by  Col.  A.  M. 
Miller,  but  it  was  thought  by  Mr.  R.  S.  Weston,  who  reported  on  the 


*  Report  of  the  Filtration  Commission.     Pittsburg,  1899. 

t  Excluding  inferior  results  obtained  during  special  experiments. 


510  RAPID   SAND   FILTRATION. 

chemical  and  biological  work,  that  a  slow  sand  filter  with  the  aid  of  a 
coagulant  would  also  give  satisfactory  results.  This  system,  however, 
was  not  tested.* 

Slow  sand  filters  were  later  installed  and  it  is  noteworthy  that  the 
results  of  their  operation  indicate  that  an  entirely  clear  effluent  cannot 
be  had  at  all  times  without  the  use  of  a  coagulant,  although  the 
bacterial  results  are  satisfactory.  (Art.  536.) 

(e)  The  New  Orleans  Experiments.  —  Extensive  experiments  were 
made  in  1901  by  Mr.  R.  S.  Weston  on  the  purification  of  the  Miss- 
issippi River  water  at  New  Orleans  by  both  slow  and  rapid  filters. 
This  water  has  an  excessive  amount  of  very  fine  sediment  (Art.  462) 
and  the  chief  problem  was  one  of  clarification  rather  than  bacterial 
purification.  It  was  found  that  either  system  would  give  satisfactory 
results  when  the  water  received  proper  preliminary  treatment,  but  that 
plain  sedimentation  was  an  inadequate  preparation  for  even  the  slow 
filters.  In  this  case  it  was  found  that  the  most  economical  method  of 
treatment  for  rapid  filtration  consisted  in  a  preliminary  period  of  plain 
subsidence  of  about  12  hours  followed  by  an  equal  period  of  subsidence 
with  coagulation.  With  slow  filters  the  second  period  of  subsidence 
could  economically  be  carried  on  for  about  24  hours.  It  was  estimated 
that  on  the  average  a  period  of  12  hours  plain  subsidence  would  reduce 
the  turbidity  to  about  485  parts  per  million,  silica  standard  (435  parts 
suspended  matter),  and  that  the  12  hour  period  of  coagulation  would 
reduce  the  turbidity  to  below  75  parts,  silica  standard.  It  was  not 
thought  economical  to  attempt  to  reduce  the  turbidity,  previous  to 
filtration,  below  50  parts,  silica  standard.  The  average  amount  of 
coagulant  required  for  a  turbidity  of  485  parts  in  the  settled  water 
would  be  4.5  grains  sulfate  of  alumina  per  gallon.  The  amount  of 
wash  water  was  estimated  at  4  per  cent.  The  most  economical  size  of 
sand  to  use  was  found  to  be  from  .30  to  .40  mm'  effective  size  with  a 
uniformity  coefficient  of  not  more  than  1.5.  A  finer  sand  would  lead 
to  too  rapid  clogging  of  the  bed,  while  a  coarser  sand  would  permit  the 
passage  of  coagulated  material  before  the  maximum  desirable  head  of 
about  10  to  12  feet  was  utilized.  A  depth  of  sand  of  2.5  feet  and  a 
rate  of  filtration  of  125,000,000  gallons  per  acre  per  day  were  con- 
sidered satisfactory.  The  cost  of  filtration,  including  capital  charges, 
was  estimated  at  $15.00  per  million  gallons. f 

*  The  results  of  the  experiments  together  with  much  other  information  on  the 
subject  of  filtration  is  contained  in  Senate  Report  No.  2380,  56th  Cong.;  second 
Session,  on  "  Purification  of  the  Washington  Water  Supply." 

t  Report  oh  Water  Purification  Investigation,  1903. 


EXPERIMENTS   ON  RAPID  FILTERS. 


546.  Tests  of  Plants  in  Operation.  —  At  Little  Falls,  N.  /.,  the 
average  results  of  the  first  five  months  of  operation  of  a  rapid  filter 
plant  were  as  follows  :  * 

RESULTS  OF  FILTRATION  AT  LITTLE  FALLS,  N.  J. 


Turbidity. 

Color. 

Bacteria. 

f  J 

Per  Cubic  Centimeter. 

1 

Month. 

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1 

1902 

Sept. 

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31 

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3900 

190 

96.5 

Oct. 

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31 

7 

3800 

650 

90 

97.6 

Nov.       . 

1*63 

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4 

2 

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28 

7 

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1  100 

60 

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Dec.       . 

1.70 

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24 

5 

5800 

1800 

50 

99.1 

1903 

Jan. 

0.84 

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5 

4000 

1700 

110 

97.2 

The  river  water  is  badly  polluted  but  is  usually  low  in  turbidity.     The 
average  period  of  coagulation  was  about  three  hours. 

At  Moline,  Illinois,  the  Mississippi  river  water  is  purified  by  means 
of  rapid  filtration,  with  coagulation  for  about  2  hours  using  iron  and 
lime  as  a  coagulant.  Average  results  obtained  in  a  test  run  of  19  days 
were  as  follows  :  f 

Bacteria  per  c.c. 

River  watei     10140. 

Settled  water 610. 

Filtered  water    31. 

Percentage  reduction 99.7 

Color,  parts  per  million. 

River  water  77. 

Filtered  water 17. 

Iron  sulfate  used,  gr.  per  gal...  1.38 

Lime  used,  gr.  per  gal .95 

The  maximum  number  of  bacteria  on  any  day  was  70.     The  turbidity 
of  the  raw  water  averaged  163  parts  per  million. 

At  the  Baisleys  and  Springfield  Filter  Plants,  two  small  plants 
of  the  Brooklyn  Water-works,  the  following  results  represent  daily 

*  Trans.  Am.  Soc  C.  E.,  1903,  L.  p.  438. 
t  Eng.  Record,  1907,  LV.  p.  708. 


512  RAPID  SAND   FILTRATION. 

analyses   for   six  weeks,  and   are  typical  of  the  work  done  at  these 
plants : 

Baisley's.  Springfield. 

Turbidity  of  raw  water  14.9  6.3 

"          "  filtered  water     .2  .41 

Color  of  raw  water 31.0  17.0 

"       "  filtered  water    3.0  i.o 

Iron  in  raw  water 1.14  -39 

"     "  filtered  water '. . . .  .03  .09 

Bacteria,  when  No.  in  raw  water  exceeded  2300. 

Raw  water 4°44-  11,251. 

Filtered  water 62.                    114. 

Percentage  reduction 98.5                   98.6 

Bacteria,  when  No.  in  raw  water   was   'less   than 
2500. 

Raw  water 1089.  1133. 

Filtered  water   23.  22. 

Percentage  reduction 97.9  98.1 

547.  Summary.  —  The  experiments  here  described,  and  the  results 
of  operation,  indicate  that  when  rapid  filters  are  properly  operated  tur- 
bidity can  be  practically  all  removed,  a  large  percentage  of  color,  and  a 
considerable  portion  of  dissolved  organic  matter.  Bacterial  results  are 
also  in  general  as  satisfactory  as  those  obtained  by  slow  sand  filters. 

To  obtain  uniformly  good  results  with  economy  requires  very  care- 
ful operation.  The  coagulant  must  be  closely  regulated  to  correspond 
with  the  quality  of  the  water,  —  in  the  case  of  waters  low  in  alkalinity 
this  is  particularly  necessary.  The  efficiency  depends  so  entirely  upon 
the  control  of  these  matters  that  the  operation  of  a  rapid  filter  involves 
greater  care  on  the  part  of  the  attendants  than  that  of  a  slow  filter.  It 
is  fully  as  important  in  this  case  also  that  the  whole  plant  should  be 
under  control  of  bacteriological  tests,  regularly  and  frequently  made. 
Many  points  of  operation,  such  as  period  between  washings,  wasting  of 
water  after  washing,  exact  amount  of  coagulant  required,  can  be  learned 
only  after  experience  in  the  light  of  such  analysis. 

Considering  the  economic  advantages  of  rapid  filters,  it  may  be  said 
that  they  are  especially  adapted  to  those  cases  where  the  cost  of  land 
is  high,  where  the  water  is  so  turbid  as  to  require  large  settling  reser- 
voirs or  the  use  of  a  coagulant,  and  in  small  plants  where  the  unit  for 
slow  filters  would  be  very  small.  They  are  also  well  adapted  for  the 
rapid  removal  of  iron  from  ground-waters,  or  of  the  precipitate  in  soft- 
ening plants.  (See  Chapter  XXIII.) 

*  Eng.  Record,  1905,  LII.  p.  238. 


i 


GENERAL   ARRANGEMENT  OF  PLANT.  513 

548.  General  Arrangement  of  a  Rapid  Filter  Plant.  —  In  a  com- 
plete rapid  .filter  plant  the  essential  elements  are:  (i)  the  coagulating 
and  settling  basin  and  appliances,  (2 )  the  filters,  and  (3)  the  clear-water 
reservoir.  In  addition  to  these  there  may  be  preliminary  settling  reser- 
voirs in  the  case  of  a  water  carrying  large  quantities  of  sediment.  Such 
reservoirs  would  usually  be  constructed  quite  separate  from  the  filter 
plant,  and,  as  regards  details,  need  not  be  considered  here.  The  coagu- 
lating basin  and  the  clear  water  reservoir  may  likewise  be  arranged  in- 
dependently of  the  filters,  but  usually  one  or  both  are  built,  with  the 
filters,  into  a  single  structure  forming  the  purification  plant.  Inasmuch 
as  the  coagulating  basin  constitutes  a  necessary  and  vital  part  of  a  rapid 
filter  plant,  and  requires  as  close  attention  as  the  filters  themselves,  it 
is  especially  important  that  the  appliances  for  operating  the  basins  and 
the  filters  be  under  the  same  roof  and  conveniently  arranged  for  operat- 
ing purposes.  The  clear-water  reservoir,  requiring  little  attention,  may 
be  located  at  any  convenient  point  near  at  hand. 

The  best  arrangement  of  parts  will  depend  much  upon  local  condi- 
tions. A  convenient  arrangement  of  filter  units,  especially  if  rectangular 
in  form,  is  similar  to  that  for  large,  slow  filters;  that  is,  to  place  them 
in  two  or  more  rows  side  by  side,  with  the  necessary  piping,  valves,  etc., 
in  a  gallery  between  the  rows.  The  coagulating  basin  may  be  conven- 
iently located  adjoining  the  filters,  and  the  clear- water  reservoir  sepa- 
rately, or,  as  is  quite  common,  immediately  underneath  the  filters.  The 
introduction  of  reinforced  concrete  makes  this  arrangement  economical 
and  satisfactory. 

Fig.  I38a  illustrates  the  arrangement  of  filters  and  coagulating  basin 
at  Youngstown,  Ohio.  The  whole  is  under  roof  and  represents  a  con- 
venient and  compact  plan.  The  clear-water  reservoir  is  located  at 
some  distance  from  the  filter  plant.  The  filter  units  are  14'  6"  x  21' 
in  size  at  the  sand  level,  and  between  the  rows  are  the  pipe  gallery  and 
operating  platforms.  Details  of  the  filter  unit  and  pipe  system  are 
shown  in  Fig.  I38b. 

Fig.  I38c  illustrates  the  general  plan  of  the  purification  plant  at 
Watertown,  N.Y.,  and  Figs.  I38d  and  1386  the  details  of  the  filter 
plant.  The  coagulating  basin  and  the  pure-water  reservoir  are  con- 
crete, vaulted  reservoirs  located  near  at  hand,  but  the  solution  tanks  and 
appliances  are  located  in  the  filter-house.  The  filter-house  roof  is 
extended  to  cover  the  operating  platform  between  the  filters  and  a  por- 
tion of  the  filters  themselves,  the  remaining  portion  being  covered  with 
a  reinforced  concrete  cover  and  earth  filling. 

Fig.   I38f  shows  the  filter  plant  at  Columbus,  O.     The  filters  are 


RAPID  SAND  FILTRATION. 


FIG.    i38a.   FILTER    PLANT    YOUNGSTON,   O. 

(From  Engineering  Record,  vol.  LII.) 


•*."•'• 

1 

•»'•'•* 

» 

•|  —  ^  •  i 

i                           1        '^  '^     -1' 

« 

»•• 
« 

*                                             VP 

».'-*.  "    '            *     ':'»  •*•'•'•*  "—  .S  .'-*.    «"""  V  '     »•  '»" 

Longrtucthal  Section  of  Rlter  and  RpeGalfery 

FIG.    i38b.   FILTER  UNIT,   YOUNGSTOWN,   O. 

(From  Engineering  Record,  vol.  LII.) 


DETAILS   OF  CONSTRUCTION  AND    OPERATION. 


515 


relatively  large  here,  each  tank  unit  being  n'  8"  x  50'  8"  in  dimen^ 
sion.  The  general  arrangement  of  filters  and  piping  is  the  same  as  in 
the  other  plants  illustrated,  the  filters  being  mostly  covered  with  rein- 
forced concrete.  The  filters  are  used  primarily  as  a  part  of  a  softening 
plant. 

In  the  large  plant  at  Cincinnati  (Fig.  I38g)  the  filters  are -arranged 
in  a  manner  similar  to  that  at  Columbus,  but  the  filter-house  extends 
entirely  over  the  filters,  an  arrangement  possessing  some  advantages  in 


Qf- Manholes. Q 

S       .R        n    •    n        a        «.       „  7  „        i 


Cl  o/'ffV 
M     ' 

M 


er  Pipe  •*. 
aw  \ 

~-'---' 


Y^Coaji//^^ 
fs  ap plied  here. 

i 


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^^^^ 

Filter     Houspi 


Pipe      Oollery. 


°l 


..... 

IVCooquMed  Httter.  |f—  - 
........     • 


ie-WPur*  Water. 


O  Coagulating    Basin.Q       T 


O  Coagulating  Basin  O  !' 

--~>'--  ~-~ 


/}   [p::fc±:;:±^^^±^±:^^^ 
114?*^°   9  -°    °    °    °    '    °  1°    ' ^°   ! 


General    Plan  of  Water  Purification  Plant. 


FIG.    1380.    FILTER  PLANT,   WATERTOWN,  N.  Y. 

(From  Engineering  Record,  vol.  XLIX.) 

regard  to  inspection  and  control.  The  clear-water  reservoir  is  under- 
neath the  filters  in  both  these  plants. 

549.  Details  of  Construction  and  Operation.  —  The  most  important 
details  of  construction  include  :  (a)  the  sand  bed  ;  (b)  the  strainer  sys- 
tem and  collecting  pipes  ;  (c)  the  agitating  system  ;  (d)  the  wash-water 
appliances  ;  (e)  means  for  controlling  the  rate  of  filtration ;  (_/")  the 
coagulating  system,  including  means  for  preparing  solutions  and  regu- 
lating their  application,  and  the  arrangement  of  coagulating  basins ; 
(g)  arrangement  of  piping  and  valves ;  and  (k)  various  other  devices 
for  operating  the  plant. 

(a)  The  Sand  Bed.  —  Experience  has  shown  that  the  most  satis- 
factory sand  is  one  of  quite  uniform  grain  and  of  an  effective  size  of 
from  .3  to  .4  mm.,  the  best  size  depending  somewhat  upon  the  character 
of  the  water  to  be  treated.  A  uniformity  coefficient  of  not  more  than 


Si6 


RAPID  SAND   FILTRATION. 


Plan     of    Fil+eys 
Top  of  niters  E 1 120  5  i 


T 


t'Opcryting  Platform  El  H8  0~-    •  •  Cpaaulateti  Wafer*.  ^  '• 


-J-r  -w 


'E1J06.Z 
,  El  1040 


^:«A^ 

Section  C-  O        ^  Minimum  Thickness  of  Floor  > 


Section    A-B.  *•  $" Steel .?<.<** 

FIG.  i38d.  FILTER  PLANT,  WATERTOWN,  N.  Y. 

(From  Engineering  Record,  vol.  XLIX.) 


DETAILS   OF  CONSTRUCTION  AND   OPERATION. 


517 


Top  of  Filter  Wall  El.  ISO.  5 


Drain  Covered  with  £ 
Strengthened  with  StccJ. 


-&W  I.  Re  wash..     Min.  Th'ckn&ss  of  Floor  6" 
't Invert  El. 102.25  Floor  Slopes  to  Drain. 

to  101.5 
Sec-Hon    on    Lme  C- D. 


of    Pipe    connections -Tor  Two  Filters.^ 


Confroiiei V--T  ; ;  i  i  \—-i 

K)"lntet+,   jijjii     ^HtKfqmrsh,  Special  Bend 


Plan    of    Piping  to  Two  Filters 

FIG.  1386.  DETAILS  OF  FILTER,  WATERTO-WN,  N.  Y. 

(From  Engineering  Record,  vol.  XLIX.) 


5i8 


RAPID  SAND  FILTRATION. 


Section   A- 8 


FIG.  i38f.  FILTER  PLANT,  COLUMBUS,  O. 

(From  Engineering  Record,  vol.  LIII.)  contvikr. 

WFitttrtd 


Secti'on  C"O. 


DETAILS  OF  CONSTRUCTION  AND  OPERATION. 


519 


1.5  is  desirable.  A  sand  of  low  uniformity  is  undesirable  as  it  tends  to 
stratification  in  washing,  and  the  finer  particles  are  likely  to  be  carried' 
away  in  the  process.  Such  a  sand  also  offers  greater  resistance  to  the 
passage  of  the  water.  A  fine  sand  also  clogs  more  quickly  than  a  coarse 
sand,  thus  increasing  the  cost  of  operation.  On  the  other  hand,  a  coarse 


Dr&ih 


FIG.  i38g.  FILTER  PLANT,  CINCINNATI,  O. 

(From  Engineering  Record,  vol.  LV.) 


sand  allows  the  sediment  to  penetrate  to  a  greater  depth,  and  if  too  coarse 
it  may  need  to  be  cleaned  before  the  maximum  available  head  has  been 
utilized.  A  depth  of  30  to  36  inches  is  usually  employed  in  the  more 
recent  plants.  The  sand  bed  is  supported  on  a  layer  of  fine  gravel,  6  to 
8  inches  or  more  in  thickness,  which  permits  the  perforations  in  the 
strainers  to  be  of  fairly  large  size.  This  gravel  should  be  carefully 


520  RAPID  SAND   FILTRATION. 

screened  and  of  as  large  a  size  as  practicable  without  allowing  the  super- 
imposed sand  to  penetrate  into  the  pore  spaces.  Usually  two  or  three 
grades  are  employed,  the  upper  one  being  about  .05  to  .1  inch  in  size, 
and  the  lower  one  about  \  to  \  inch.  The  gravel  should  be  free  from 
fine  material,  and  as  uniform  as  possible  in  order  to  avoid  being  dis- 
turbed in  the  washing  process.  Crushed  and  screened  quartz  is  often 
used  for  the  sand  and  gravel,  but  natural  materials  well  screened  are 
equally  satisfactory. 

(b).  The  Strainer  System  and  the  Collecting  Pipes.  —  The  design  of 
the  strainer  and  collecting  system  is  a  matter  of  greater  difficulty  than 
in  the  case  of  the  slow  sand  filter.  As  in  that  type,  the  collecting 
system  must,  first  of  all,  be  sufficiently  extensive  to  cause  the  total  loss 
of  head  to  be  nearly  uniform  over  the  entire  area.  If  this  were  the 
only  requirement  it  could  readily  be  met  by  the  use  of  coarse  gravel 
and  drain  pipes  with  large  openings.  The  strainer  system,  however, 
must  serve  also  to  distribute  the  wash  water  uniformly  into  the  sand 
bed.  To  accomplish  this  there  must  be  a  considerable  resistance  to 
flow  through  the  strainer,  as  compared  to  that  through  the  pipe  system, 
so  that,  as  the  water  forces  its  way  through  the  sand,  a  considerable 
reduction  of  resistance  in  the  sand  at  one  point  will  not  materially 
change  the  pressure  at  other  points.  This  requires  the  strainer  open- 
ings to  be  small,  numerous,  and  well  distributed,  and  the  pipe  system 
to  be  relatively  large  and  arranged  so  as  to  give  practically  equal 
pressures  at  all  points.  The  collecting  pipes  must  be  designed  with 
reference  especially  to  the  amount  of  wash  water  required  and  must 
be  arranged  in  units  of  not  too  large  size.  The  unit  of  area  served  by 
one  collecting  main  is  commonly  made  from  10  to  15  feet  wide  by  15 
to  20  feet  long.  In  large  plants  it  is  convenient  to  group  together  from 
two  to  four  such  units  to  serve  a  single  tank,  the  size  of  tank  depending 
much  upon  the  total  size  of  plant. 

Figs.  137,  138,  and  I38b  illustrate  common  arrangements  of  collect- 
ing pipes  and  strainers.  In  each  case  the  effluent  pipe  connects  with  a 
large  central  cast-iron  collector,  or  "mainfold,"  into  which  are  screwed 
lateral  collecting  pipes  placed  about  6  inches  apart.  Into  these  are 
screwed  brass  strainers  which  are  also  spaced  about  6  inches  apart. 
These  strainers  are  perforated  with  numerous  small  holes.  In  the  earlier 
practice  the  holes  were  very  small,  but  in  later  plants  they  are  made 
larger,  Jg  inch  to  -/%  inch  being  a  common  size.  Large  holes  are  less  apt 
to  clog  up,  and,  with  the  use  of  gravel  beneath  the  sand,  are  much  more 
satisfactory. 

The  general  arrangement  of  collecting  pipes  in  the  Watertown  plant 


DETAILS  OF  CONSTRUCTION  AND  OPERATION. 


521 


(Fig.  1380!)  is  the  same,  but  the  strainers  are  here  made  of  small  brass 
tubes,  attached  by  means  of  T's  to  the  laterals  of  2-in.  wrought-iron 


Details    of   Collector  and    Air   Syster 
s-"i*  Extra  Strong  w.l.  Pipe  Lateral  Co/lectors. 


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FIG. 


Port     Sectional  Elevation. 

.  STRAINER  SYSTEM,  WATERTOWN  FILTERS. 

(From  Engineering  Record,  vol.  xnx.) 


pipe.     Details  of   this  strainer  system  are  shown  in  Fig.   I38h.     The 
laterals  are  about  10  inches  apart  and  the  strainers  6  inches. 

In  some  of  the  latest  plants  the  laterals  consist  mainly  or  wholly  of 
channels  in  the  concrete  floor,  and  the  strainers  are  made  of  brass  plates 


522 


RAPID  SAND   FILTRATION. 


set  directly  into  this  floor.  Fig.  1381  illustrates  such  a  system  as  em- 
ployed in  the  Columbus  plant.  The  strainer  itself  is  a  brass  plate  perfor- 
ated with  ^g-in.  holes.  These  plates  are  set  into  slabs  of  reinforced  con- 
crete on  8|-in.  centers,  which  in  turn  are  set  into  the  concrete  floor  8} 
inches  apart.  Below  these  slabs  are  lateral  channels,  as  shown  in  the  sec- 
tion. Between  the  rows  of  strainers  triangular  concrete  ridges  are  con- 
structed in  the  floor  to  a  height  of  3  inches  above  the  strainer  level. 


DETAILS  OF  STRAINER 


A 


'..''>*>. 

!  i  m  '  Wf  '   ' "    .^%v:W^-^':>;-'V4j    aW&£% "»    ~rr ;    •""  ':'^^:-(x:'~',-:- 

W^^  *  '•.•^.cr^L^Lj  I ^--ci_i±i2A;vl |;  < , 


FIG.  138!.  STRAINER  SYSTEM,  COLUMBUS  FILTERS. 

(From  Engineering  Record,  vol.  till.) 


The  furrows  between  are  filled  with  gravel,  which  also  extends  a  few 
inches  above  the  ridges.  This  arrangement  aids  in  securing  a  good  dis- 
tribution of  the  wash  water.  The  collecting  unit  is  1 1'  8"  square,  at 
the  center  of  which  is  a  cast-iron  connection  with  the  main  effluent  pipe. 
Four  such  units  make  up  one  tank  unit,  and  two  such  tank  units  are 
operated  together  in  pairs  as  a  single  filter  unit.  Fig.  I38f  shows  the 
arrangement  of  collecting  pipes  leading  from  the  collecting  unit,  and  it 
will  be  noted  that  the  length  of  the  pipe,  up  to  its  connection  to  the 
filter,  is  the  same  for  all  units,  thus  causing  a  uniform  resistance  to 
flow  in  the  pipe  system. 

Fig.  138]  shows  a  somewhat  similar  detail  adopted  for  the  Cincin- 
nati plant.  The  laterals  consist  of  concrete  channels  1 2  inches  apart, 
with  strainers  of  long,  brass  plates,  perforated  with  sixty-four  ^-in. 


DETAILS  OF  CONSTRUCTION  AND  OPERATION. 


523 


holes  per  lineal  foot.  From  each  of  these  lateral  channels,  connections 
are  made  by  means  of  3^-in.  cast-iron  risers  to  the  main  collector 
located  beneath  the  floor.  The  furrows  in  the  concrete  floor  are  8  inches 
deep  and  contain  all  the  gravel.  Above  this  gravel  is  placed  a  wire 
screen  of  No.  20  brass  wire,  having  10  meshes  per  inch.  The  purpose 
of  this  screen  is  to  hold  the  gravel  in  place  during  washing,  the  water- 
pressure  employed  here  being  especially  high,  as  no  other  method  of 
agitation  is  used.  The  units  of  the  collecting  system  are  \2\r  X  14' 
and  four  such  units  make  up  one  tank  unit.  The  filter  unit  comprises 


FIG.  138}.  STRAINER  DETAIL,  CINCINNATI  FILTERS. 

(From  Engineering  Record,  vol.  LV.) 


two  tanks  as  in  the  Columbus  plant,  thus  giving  a  filter  unit  of  28'  X 
50'  net  area.  In  the  New  Orleans  plant  the  same  general  system  has 
been  adopted,  no  air  being  used  in  cleaning. 

(c)  The  Agitating  System.  —  Two  general  methods  of  agitating  the 
sand  are  in  use,  the  mechanical  agitator  and  agitation  by  compressed  air. 
The  usual  form  of  the  mechanical  agitator  is  illustrated  in  Fig.  137. 
It  consists  of  deep  rakes  which  are  moved  through  the  sand  during 
the  washing  process..  After  the  operation  is  complete  the  rakes 
are  lifted  out  of  the  sand.  While  the  circular  form  of  tank  is  better 
adapted  to  the  use  of  this  form  of  agitator  it  has  been  used  to  some 
extent  with  rectangular  tanks,  but  compressed  air  is  much  more  con- 
venient in  that  case. 

In  the  use  of  compressed  air,  the  air,  under  a  pressure  of  3  to  5  Ibs., 
is  forced  through  the  sand  bed,  either  through  the  strainer  system 
itself  or  through  a  separate  pipe  system  located  in  the  gravel  just  above 
the  strainers.  In  the  air  distributing  system,  as  in  the  water  system,  it 


524  RAPID  SAND  FILTRATION. 

is  necessary  to  use  such  an  area  of  openings  as  to  admit  the  desired 
amount  of  air  and  at  the  same  time  to  offer  a  considerable  resistance  to 
exit  as  compared  to  the  resistance  in  the  pipe  system.  These  require- 
ments make  it  necessary  to  use  a  much  smaller  total  area  of  openings 
than  in  the  water  system,  an  area  of  .02  to  .03  sq.  in.  per  sq.  ft.  of 
filter  being  common.  Where  the  air  is  forced  through  the  strainer 
system  an  ingenious  arrangement  of  the  strainer  traps  off  the  main 
opening,  so  that  the  opening  for  air  is  reduced  to  the  desired  amount. 
In  this  case  the  air  pipes  are  connected  at  intervals  with  the  collecting 
main,  through  which  the  air  passes  to  the  trapped  strainers.  In  the 
operation  cf  washing,  air  and  water  are  used  alternately. 

Fig.  I38g  shows  the  details  of  the  air  system  in  the  Watertown 
plant.  The  pipes  consist  of  small  slotted  brass  tubes  spaced  about 
4  inches  apart.  At  Columbus  the  air  is  conveyed  through  separate 
brass  air  tubes  placed  2  feet  II  inches  apart  and  supported  about 
6  inches  above  the  strainers. 

In  some  plants  water  alone  is  successfully  used  without  other  means 
of  agitation,  notable  examples  being  the  large  plants  at  Cincinnati  and 
New  Orleans.  In  these  plants  no  provision  is  made  for  special  agitation, 
but  the  wash  water  is  used  under  relatively  high  pressure.  Experience 
in  some  plants  indicates  that  the  results  gradually  deteriorate  if  water 
alone  is  used,  although  at  first  there  appears  to  be  no  difference. 

(d)  Wash-water  Appliances.  —  The  wash-water  appliances  consist  of 
the  pipe  connections,  arranged  so  that  the  flow  may  be  reversed  in 
direction,  the  agitating  system,  and  the  means  for  taking  off  the  dirty 
water  from  above  the  filter.  The  wash  water  is  supplied  under  a 
pressure  of  about  10  to  15  Ibs.  either  by  means  of  suitable  pumps,  or 
from  the  high  pressure  system  through  reducing  valves,  the  former 
being  generally  the  more  economical  method.  It  is  admitted  to  the 
effluent  pipe  of  the  filter  through  suitable  pipe  connections  and  con- 
trolling valves.  The  dirty  water  from  the  filter  passes  through  troughs 
or  gutters  built  across  the  bed  or  at  the  margin,  and  thence  is  conducted 
through  pipes  to  the  drain.  In  order  readily  to  carry  off  the  wash 
water  the  gutters  need  to  be  spaced  so  that  the  lateral  movement  of 
the  water  is  relatively  small,  not  more  than  3  to  4  feet.  These  gutters 
are  conveniently  built  of  reinforced  concrete.  Various  arrangements 
are  shown  in  the  illustrations.  In  Fig.  137  a  wooden  gutter  extends 
around  the  tank  along  the  inside  surface;  in  Fig.  138  two  gutters  are 
constructed  along  the  outside  walls  and  a  central  trough  of  steel  is  also 
provided.  In  Fig.  I38b  a  somewhat  similar  arrangement  is  used.  In 
Fig.  I38d  two  gutters  of  steel  are  employed,  while  in  Fig.  I38f  rein- 


DETAILS  OF  CONSTRUCTION  AND  OPERATION.  525 

forced  concrete  gutters  are  used,  spaced  about  7^  feet  apart  and  leading 
to  a  central  gutter  between  adjoining  beds.  The  gutters  are  placed 
about  i  foot  above  the  surface  of  the  sand  bed.  Generally  the  un fil- 
tered water  is  admitted  through  the  same  pipe  connection  that  serves 
as  the  outlet  for  the  wash  water,  the  gutters  thus  serving  as  weirs  to 
distribute  the  raw  water  until  the  filter  is  partially  filled.  After  wash- 
ing a  filter  it  is  sometimes  desirable  to  waste  the  effluent  for  a  time. 
Provision  should  always  be  made  for  this  by  constructing  suitable  con- 
nections from  the  effluent  pipe  to  the  drain.  The  time  required  for 
washing  is  only  10  to  12  minutes,  and  the  amount  of  wash  water 
required  is  usually  from  4  to  5  per  cent  of  the  total  amount  filtered. 

(e]  Head  Employed  and,  Manner  of  Controlling  Rate  of  Filtration. 
—  At  the  ordinary  rate  of  loo  to  125  million  gallons  per  acre  per  day, 
the  minimum  frictional  resistance  is  usually  from  2  to  3  feet.  As  in 
the  slow  sand  filter,  arrangements  must  be  made  whereby,  as  the  filters 
become  clogged,  this  loss  of  head  may  be  increased  up  to  the  maxi- 
mum desirable  amount,  and  so  varied  as  to  maintain  a  uniform  rate  of 
filtration.  The  maximum  loss  of  head  is  generally  made  about  10  or  12 
feet.  A  greater  maximum  tends  to  increase  the  cost  of  plant  and  the 
penetration  of  suspended  matter  into  the  filter,  while  a  lesser  maxi- 
mum tends  to  increase  the  frequency  and  cost  of  cleaning  and  the  pro- 
portion of  area  out  of  service.  With  this  maximum  available  head  the 
period  of  service  will  usually  range  from  6  to  12  hours. 

The  head  is  controlled  in  a  manner  similar  to  that  used  with  slow 
filters,  that  is,  by  maintaining  a  constant  level  of  water  on  the  filters 
and  varying  th :  pressure  head  in  thv-  effluent  pipe  by  some  means  more 
or  less  automatic.  Generally  automatic  controllers  are  used,  a  con- 
troller being  inserted  in  the  effluent  pipe  of  each  filter  unit.  A  form 
used  by  the  Jewell  Filter  Company  is  one  designed  by  Mr.  E.  B. 
Weston,  and  known  by  his  name.  The  discharge  is  controlled  by  two 
butterfly  valves  which  are  regulated  by  a  float  so  as  to  give  a  constant 
head  over  an  annular  opening  through  which  the  water  is  discharged. 
The  annular  opening  may  be  varied  in  size  by  the  use  of  various  sized 
central  disks.  The  controller  is  enclosed,  but  the  discharge  side  is  not 
under  pressure.*  A  design  used  at  the  Watertown  plant  is  illustrated 
in  Fig.  1 38k.  Here  a  regulating  gate  or  valve  acts  as  an  orifice  plate, 
thus  enabling  the  rate  to  be  more  readily  varied.  The  piston,  or 
pressure  disk,  is  under  pressure  on  its  upper  side  from  the  down-stream 
side  of  the  regulating  valve  and  on  its  lower  side  from  the  up-stream  side 

*  See  Eng.  Record,  Nov.  25,  1899. 


526 


RAPID   SAND   FILTRATION. 


4" 'Connection  Pipe 
T  to  Downstream  side, 
tmg  Valve. ' 


of  the  valve,  vibration   being    checked   by   transmitting    the  pressure 
through  small  openings  in  a  stilling  disk.     A  type  of  controller  similar 

to  the  automatic  weir  and  float  used  at 
Pittsburg  is  employed  at  Hackensack, 
N.Y.*  Various  other  devices  are  used 
for  this  purpose,  but  those  described 
represent  the  most  common  types. 

The  means  employed  to  maintain 
a  constant  level  of  water  on  the  filter 
is  the  usual  balanced  valve  placed  on 
the  entrance  pipe  and  regulated  by  a 
float.  A  butterfly  valve  is  also  often 
employed  for  this  purpose.  Generally 
the  level  of  water  in  the  entire  system 
of  filters  is  maintained  at  a  uniform 
elevation,  and  equal  to  that  in  the 
coagulating  basin,  so  that  the  regulat- 
ing valves  are  placed  in  the  basin  only. 
The  most  suitable  arrangement  de- 
pends upon  local  conditions. 

(/)  The  Coagulating  System.  — 
The  various  parts  of  the  coagulating 
system  are  the  same  as  described  in 
Chapter  XX.  The  period  of  coagula- 
tion is  important  as  the  success  of 
the  plant  depends  much  upon  this 
feature.  In  the  early  plants  this 
was  very  inadequate,  being  but  a 
few  minutes.  Generally  a  period  of  3  to  6  hours  is  now  provided,  the 
most  advantageous  period  depending  upon  the  character  of  the  water. 
Too  perfect  sedimentation  is  undesirable  as  it  removes  too  fully  the 
coagulum  upon  which  the  efficiency  of  the  filter  depends.  The  coagu- 
lating basin  of  the  Youngstown  plant  is  well  shown  in  Fig.  I38a.  Here 
the  effluent  passes  over  a  broad  weir  into  the  pipes  leading  to  the  filters. 
(g)  Arrangement  of  Piping  System. — The  pipe  system  includes 
the  following :  Inlet  pipes  for  the  raw  water,  outlet  pipes  for  effluent, 
pipes  for  wash  water,  pipes  for  wasting  dirty  water  to  the  drain,  pipes 
for  wasting  effluent,  and,  generally,  air  pipes.  The  large  mains  of  these 
various  systems  are  generally  placed  in  a  pipe  gallery  between  rows  of 


Section     A-B. 
Sections   of   Part  of  Controller. 

FIG.   i38k.     CONTROLLER,  WATERTOWN 
FILTERS. 

(From  Engineering  Record,  vol.  XLIX.) 


Eng.  Record,  1904,  L.  p.  591. 


DETAILS  OF  CONSTRUCTION  AND  OPERATION.  $2? 

filters  and  branches  taken  off  at  each  filter  as  shown  in  several  of  the 
illustrations.  In  the  large  units  at  Columbus  and  Cincinnati  the  filter 
unit  is  divided  in  the  center  by  a  horizontal  gutter  into  which  the  raw 
water  is  discharged,  and  which  also  receives  the  dirty  water  in  washing. 
The  air  pipe  connections  are  also  made  by  means  of  branches  taken  off 
in  the  central  channel  (see  Fig.  I38f).  The  branch  pipes  from  the  raw- 
water  main  and  from  the  waste-water  main  usually  connect  to  the  same 


FIG.  138!.     OPERATING  ROOM,  YOUNGSTOWN  FILTERS. 

(From  Engineering  Record,  vol.  LII.) 

point  in  the  filter  ;  likewise  the  branches  from  the  effluent  and  from 
the  wash-water  mains.  An  additional  cross  connection  is  placed  be- 
tween the  effluent  pipe  and  the  waste  pipe  to  permit  of  wasting  the 
effluent. 

(//)  Other  Devices  Used  in  Operating  the  Plant.  —  Besides  the 
features  already  described,  other  details  which  require  careful  attention 
are  the  various  devices  used  in  the  operation  of  the  plant.  For  the 
operation  of  the  valves  hydraulic  pressure  is  generally  employed,  the 
pressure  pipes  being  all  operated  from  tables  on  the  operating  platform. 
Fig.  138!  shows  the  operating  room  of  a  modern  plant.  Loss-of-head 


528  RAPID   SAND   FILTRATION. 

gauges  and  water-level  gauges  should  be  provided,  as  in  a  slow  filter 
plant,  also  convenient  means  for  sampling.  Proper  laboratory  facilities 
for  the  study  and  control  of  the  operation  are  important. 

550.  Cost.  —  The  cost  of  a  rapid  filter  plant  under  ordinary  condi- 
tions will  range  from  $8,000  to  $12,000  per  million  gallons  capacity,  for 
filters,  coagulating  basin,  clear-water  well,  and  auxiliary  pumping  appa- 
ratus. The  cost  of  operation  is  largely  dependent  upon  the  amount  of 
coagulant  used.  The  cost  of  sulphate  of  alumina  is  about  $20  to  $25 
per  ton,  equivalent  to  $1.40  to  $1.7 5  per  million  gallons  for  each  grain 
per  gallon  used.  Sulphate  of  iron  costs  about  $10  to  $12  per  ton,  and 
lime  $4  to  $6.  Compared  to  the  cost  of  sand  filters  the  first  cost 
will  usually  be  less,  but  if  much  coagulant  is  used  the  cost  of  operation 
will  be  more.  Which  system  is  the  more  economical  thus  depends 
upon  the  character  of  the  water  treated  and  other  local  conditions. 
Under  ordinary  conditions  the  cost  of  operation  per  million  gallons 
will  range  from  $4  to  $6  ;  and,  including  capital  charges,  interest 
and  depreciation,  the  total  cost  will  range  from  $10  to  $12  per  million 
gallons. 

LITERATURE. 

(See  also  references  in  Chapter  XIX.) 

1.  Weston.     Rhode  Island  State  Board  of  Health  Report,  1894.     Experi- 

ments at  Providence. 

2.  Various  Systems  of  Filtration  at  Denver,  Colo.     Eng.  News,  1894,  xxi. 

p.  83. 

3.  The    Jewell  Mechanical   Water  Filter  in  Nineteen  Cities.     Eng.  News, 

1896,  xxxv.  p.  354. 

4.  Hazen.     Report  on  the  Mechanical  Filtration  of  the  Public  Water-supply 

of  Lorain,  O.     Ohio  State  Board  of  Health  Report,  1897,  p.   154. 
Abstract,  Eng.  News,  1897,  xxxvm.  p.  278. 

5.  Water  Purification  at  Vincennes,  Ind.     Eng.  News,  1900,  XLIII.  p.  291. 

6.  Water  Purification  at  Norfolk,  Va.     Eng.  News,  1900,  XLIII,  p.  346. 

7.  Weston.    Test  of  a  Mechanical  Filter  (East  Providence,  R.  I.).       Trans. 

Am.  Soc.  C.  E.,  1900,  XLIII.  p.  69. 

8.  The  Efficiency  of  the  East  Providence  Mechanical  Filters.     Eng.  Record, 

1901,  XLIV.  p.  545- 

9.  A  Mechanical  Filter  Plant  for  the  Ithaca  Water-works  Company.     Eng. 

Record,  1903,  XLVIII.  p.  237. 

10.  Weston.     Report  on  Water  Purification  Investigation  of  the  Mississippi 

River  Water  at  New  Orleans,  1903.     Public  Doc. 

11.  Fuller.     The   Filtration  Works  of   the  East  Jersey  Water  Company,  at 

Little  Falls,  New  Jersey.     Trans.  Am.  Soc.  C.  E.,  1903,  L.  p.  394. 

12.  A    Rapid    Filter    Plant   for   the    New    Chester  Water  Company.     Eng. 

Record,  1904,  XLIX.  p.  245. 

13.  Recent  Concrete-Steel  Water-works  Construction  at  Ithaca,  N.  Y.     Eng. 

Record,  1904,  XLIX.  p.  444. 


LIT  ERA  TURE.  5  29 

14.  A  Mechanical  Filtration  Plant  for  Watertown,  New  York.     Eng.  Record, 

1904,  XLIX.  p.  640  et  seq. 

15.  The    Mechanical    Filters   of   the    Hackensack   Water   Company,     Eng. 

Record,  1904,  L.  p.  572. 

16.  Weston.     The  American  System  of   Filtration  Plant  in  Mysore,  India. 

Eng.  Record,  1904,  L.  p.  704. 

17.  Levi  Mechanical  Filters  at  Charleston-Kanawah,  W.  Va.     Eng.  News, 

1904,  LI.  p.  326. 

18.  Whipple.     Mechanical  Filter  at  Binghamton,  N.  Y.     Eng.  Record,  1905, 

LI.  p.  683. 

19.  The    Mechanical    Filters    at   Youngstown,  O.     Eng.  Record,   1905,    LII. 

p.  409. 

20.  Mechanical  Filters  of  the  Brooklyn,  N.  Y.,  Water  Works.     Eng.  Record, 

1905,  LII.  p.  237. 

21.  Mead.       Recent   Improvements   in   the    Plant   of  the    Danville   Water 

Company.     Jour.  West.  Soc.  Engrs.,  1905,  x.  p.  272. 

22.  Weston.     New   Water    Purification    Plant   at   Paris,  Ky.      Eng.  News, 

1906,  LV.  p.  494. 

23.  The  Baiseley's,  Springfield,  Forest  Stream,  and  Hempstead  Filter  Plants, 

Borough  of  Brooklyn,  New  York.     Eng.  News,  1906,  LVI.  p.  195. 

24.  Blagden.     The  Filtration-works  for  Supplying   the  Town  of  Alexandria 

with  Potable  Water.     Proc.  Inst.  Civ.  Eng.  No.  3615. 

25.  Milligan.     The   Development   of   Mechanical   Filtration.      Jour.    West. 

Soc.  Eng.,  1906,  XL  p.  503. 

26.  The  Mechanical  Filters  of  the  Water-works  of  Harrisburg,  Pa.     Eng. 

Record,  1907,  LV.  p.  315. 

27.  Monahan.      The    Cincinnati   Water    Purification    Plant.      Eng.  Record, 

1907,  LV.  p.  430. 

28.  Improvements  to  the  Water-supply  System  of  Albany,  N.  Y.     Installa- 

tion of  Rapid  Filters  for  preliminary  filtration.     Eng.  Record,  1907, 
LV.  p.  609. 

29.  The   Water  Filtration  Plant  at  Moline,  111.     Eng.  Record,   1907,  LV.  p. 

70S- 

30.  Burgess.     The  Development  of  the  Mechanical  Filter  Plant.     Proc.  Ohio 

Engineering  Soc.,  1908.     Eng.  News,  1908,  LIX.  p.  249. 


CHAPTER    XXIII. 
MISCELLANEOUS    PURIFICATION    PROCESSES. 

554.  Special  Forms  of  Filters.  —  Besides  the  two  principal  types  of 
sand  filters  discussed  in  the  preceding  chapters,  various  special  forms 
of   sand    niters,  and    filters    composed    of   other   materials,  have    been 
employed  to  a  limited  extent.     Two  types  of  these  are  of  considerable 
importance   and    will    be   briefly   described.     These   are  the  artificial, 
porous  stone  filter,  represented  chiefly  by  the  Fischer  system  in  muni- 
cipal plants  and  the  porcelain  filters  for  household  use,  and  the  rapid, 
coarse  filter  employed  for  preliminary  treatment  such  as  the  Maignen 
"scrubber."     The  use  of  asbestos  for  a  filter  membrane  in  domestic 
filters,  and  recently  as  an  aid  in  sand  filtration  at  South  Bethlehem, 
should  also  be  noted.* 

555.  The  Fischer    Tile  Filter.  —  This    form  of  filter,  invented  by 
Director  Fischer  of  the  water-works  of  Worms,  Germany,  and  used  at 
that  place,  consists  of  a  series  of  hollow  cells  composed  of  a  mixture 
of  sand  and  glass  fused  together.     The  cells  are  about  3  feet  square 
and  8  inches  thick,  with  a  hollow  space  of  about   I  inch.     They  are  set 
up  on  edge  in  a  reservoir  containing  the  water  to  be  filtered,  and  con- 
nected together  in  groups  so  that   the  water  filters  through  into  the 
interior   space   and  thence   passes  out    through    suitable  pipes.     The 
filters  are  cleaned  by  reversing  the  flow,  and  by  washing  with  a  hose- 
stream.     They  can    also   be   sterilized  by  steam.      The  rate  of  filtra- 
tion practiced  at  Worms  is  about  3  million  gallons  per  acre  per  day, 
but  the  actual  space  occupied  by  the  filters  is  only  about  one-fourth 
that  of  an  ordinary  filter.     The  results    obtained  compare  very  favor- 
ably with   those   from  sand  filters.     The  system  is  in  use  in    several 
places   in    Europe.     Several   cells  were    experimented   upon   at    Pitts- 
burg,  but  thoy  were  not  found  very  well  suited  for  so  turbid  a  water, 
the  preliminary  treatment  there  required  accomplishing  nearly  all  the 
purification.     Other  forms  of  stone  filters  have  been  less  extensively 
employed. 

556.  The  Maignen   "Scrubber"  —  This  is  a  form  of   preliminary 
filter,    composed    of   layers    of   coarse   gravel   and    slag   covered    with 


*  Eng.  Record,  1905,  LII.  p.  61. 


SPECIAL   FORMS  OF  FILTERS. 


531 


a  layer  of  compressed  sponge.  The  water  enters  at  the  bottom 
and  flows  upwards,  the  rate  being  ordinarily  about  60,000,000  gallons 
per  acre  per  day.  Generally  about  60  per  cent  of  the  turbidity  and 
75  to  80  per  cent  of  the  bacteria  are  removed.  The  action  is  partly 
sedimentation  and  partly  filtration.  It  is  estimated  at  Philadelphia  that 
preliminary  treatment  with  this  "scrubber,"  will  enable  the  sand  filters 


Longitudinal  Soct'iorx 

FIG.  139.    MAIGNEN  "  SCRUBBER." 

(From  Engineering  Record,  vol.  LII.) 

to  operate  satisfactorily  at  about  6,000,000  gallons  per  acre  per  day 
with  a  considerable  saving  in  cost  over  a  larger  plant  of  slow  sand 
filters.  Scrubbers  of  the  Maignen  type  are  also  used  at  South  Beth- 
lehem, Pa.  Here  they  are  composed  of  the  following  layers.  (Fig 
139):  The  lower  foot  is  made  up  partly  of  3-in.  gravel  and  partly  of 
3-in.  coke.  Above  this  are  four  layers  of  i^-in.  coke  of  a  total 
thickness  of  2  feet.  In  each  layer  are  placed  regular  rows  of  slates 


532 


MISCELLANEOUS  PURIFICATION  PROCESSES. 


inclined  about  30°,  but  in  opposite  directions  in  the  different  rows. 
Above  these  layers  is  another  layer  of  i|-in.  coke  and  finally  a  layer 
of  about  8  inches  of  compressed  sponge.  The  slate  layers  are  intended 
as  deflectors  to  aid  sedimentation.  The  scrubber  is  cleaned  by  revers- 
ing the  flow  of  water.  The  sponge  is  also  removed  and  washed  occa- 
sionally and,  if  necessary,  the  coke  may  be  treated  in  the  same  way. 
The  rate  of  filtration  through  the  scrubbers  is  28,000,000  gallons  per 
acre  per  day  and  7,000,000  through  the  sand  filters.  A  further 
increase  in  the  rate  of  the  sand  filters  to  9,000,000  gallons  has  been 
accomplished  by  adding  a  membrane  of  asbestos  fibre  to  the  top  of  the 
filter.* 

557.  Domestic  Filters.  —  Frequently  it  is  advisable  to  purify  water- 
supplies   for    household    use.     For  this   purpose   a  large  number   of 

different  filters  have  been  devised,  but 
many  of  these  are  so  inefficient  as  to 
be  worse  than  useless  ;  for  it  not  in- 
frequently happens  that  the  posses- 
sion of  a  filter  lulls  the  consumer  into 
a  state  of  false  security.  The  best  of 
these  filters  suitable  for  household  use 
are  those  that  are  made  of  unglazed 
porcelain  (Pasteur  filter),  or  fine  in- 
fusorial earth  (Berkefeld  filter). 

Filters  of  this  class  are  compara- 
tively porous,  thus  permitting  a  fairly 
rapid  flow.  In  this  respect  the  Berke- 
feld is  superior,  as  it  filters  consider- 
ably faster  than  the  Pasteur.  Both 
of  these  filters  deliver  a  wholly  germ- 
free  filtrate  when  they  are  first  put 
in  service,  but  unless  close  attention 
is  given  them  they  sooner  or  later 
lose  this  property.  The  pore  spaces  in  filters  of  this  class  are  not 
smaller  than  the  bacteria  that  ordinarily  abound  in  the  raw  water ; 
hence  the  removal  of  these  organisms  is  not  purely  mechanical.  There 
seems  to  exist  a  sort  of  attraction  between  the  bacteria  and  the  particles 
composing  the  filter,  so  that  the  former  are  prevented  from  being  forced 
through  the  pores.  This  attractive  property  varies  with  different 
materials.  Guinochet  states  that  the  pores  in  the  micro-membranes  of 


a  b 

FIG.  i39a.    PASTEUR  FILTER. 
a,  view  from  outside. 
fc,  sectional  view. 


*  Eng.  Record,  1905,  LII.  p.  61. 


SPECIAL  FORMS  OF  FILTERS.  533 

the  asbestos  filter  made  by  Breyer  are  smaller  than  in  the  Pasteur  filter 
and  yet  bacteria  pass  these  quite  readily.  As  additional  water  is 
passed  through  these  filters,  the  pore-spaces  become  reduced  in  size, 
owing  to  the  accumulation  of  organic  or  other  matter,  until  finally  a 
living  pellicle  or  membrane  is  formed  on  the  outer  filtering  surface. 
This  increases  the  resistance  offered  to  the  passage  of  the  water  and 
consequently  diminishes  the  flow  of  the  effluent.  The  bacteria  that 
abound  in  this  slimy  pellical  are  not  destroyed,  and  if  the  temperature 
is  favorable  they  begin  to  grow.  Under  such  conditions,  the  bacteria 
capable  of  multiplication  force  their  way  through  the  pores  of  the  filter 
and  so  appear  in  the  filtrate.  Filters  of  this  class  therefore  retain  their 
germ-proof  qualities  for  periods  that  are  in  a  way  inversely  proportional 
to  the  temperature  of  the  water.  The  lower  the  temperature  of  the 
water,  and  therefore  the  slower  the  development  of  the  contained 
bacteria,  the  longer  the  filtrate  will  retain  its  sterile  condition.  Gen- 
erally speaking,  these  filters  should  be  cleaned  and  sterilized  in  boiling 
water  or  in  steam  under  pressure  once  a  week  in  order  to  kill  out  the 
germ-life  that  has  found  lodgment  in  the  pores.  In  this  way  not  only 
is  the  sterility  of  the  filtrate  maintained,  but  the  yield  of  filtered  water 
is  increased.  The  more  rapid  rate  of  filtration  in  the  Berkefeld  as 
compared  with  the  Pasteur  filter  makes  this  filter  lose  its  efficiency 
more  rapidly. 

It  is  necessary  to  test  the  soundness  of  these  filters  before  they  are 
installed.  This  can  be  done  by  compressing  the  air  in  one  just  after  it 
has  been  boiled  and  then  immersing  the  same  in  water.  In  a  perfectly 
sound  filter  (Pasteur)  no  bubbles  of  air  should  be  observed. 

Although  it  is  a  demonstrated  fact  that  the  normal  water  bacteria 
will  work  their  way  through  these  filters  in  the  course  of  a  few  days  to 
a  few  weeks,  still  it  is  by  no  means  so  certain  that  disease  organisms 
like  typhoid  and  cholera  would  do  so.  Experiments  which  have  been 
made  by  adding  cultures  of  these  organisms  to  water  and  then  filtering 
the  same  have  shown  that  these  filters  kept  back  the  disease  bacteria 
for  several  weeks,  but  that  finally  they  could  be  detected  in  the 
filtrate.  When,  however,  the  amount  of  organic  matter  added  was  less, 
and  the  conditions  therefore  simulated  more  nearly  those  that  would 
obtain  in  a  polluted  water,  the  typhoid  germ  failed  to  appear  in  the 
filtrate.* 

In  times  of  epidemic  disease  entire  reliance  should  not  be  placed  in 
the  operation  of  these  filters,  as  it  frequently  happens  that  some  of 

»  S chofer,  Cent.  f.  Bakt,  1893,  xiv.  p.  685. 


534  -      MISCELLANEOUS  PURIFICATION  PROCESSES. 

them  are  defective.  An  outbreak  of  145  cases  of  cholera  in  a  single 
regiment  of  650  men  occurred  in  1894  in  Lucknow,  India,  as  a  result 
of  an  imperfect  filter  in  use  in  the  barracks ;  but  in  general  the  use  of 
the  best  niters  has  reduced  the  amount  of  water-borne  disease.  This 
is  especially  noteworthy  in  the  garrisons  of  the  French  army,  where  the 
typhoid  death-rate  has  been  much  lessened.  Rideal  mentions  an 
instance  in  the  barracks  at  Melun.  In  1889  there  were  122  deaths 
from  this  disease ;  after  the  introduction  of  the  Pasteur  filter,  the 
average  mortality  for  the  next  seven  years  was  only  seven. 

Filters  of  this  class  are  not  often  used  for  city  supplies,*  but  are 
admirably  adapted  for  schools  and  other  public  institutions. 

Other  types  of  household  filters,  such  as  those  constructed  of  porous 
stone,  charcoal,  or  asbestos,  have  been  on  the  market  for  many  years. 
Judged  from  the  popular  standpoint  of  purity,  which  is  generally  the 
production  of  a  clear  water,  many  of  the  filters  would  be  regarded  as 
quite  satisfactory,  but  as  a  means  of  removing  germ-life  they  possess  for 
the  most  part  but  little  merit.f 

558.  Aeration.  —  Attempts  have  often  been  made  to  purify  water  of 
organic  matter  by  aeration.  The  presence  of  oxygen  is  certainly 
necessary  for  the  action  of  the  nitrifying  organism,  and  experiments  of 
the  Massachusetts  Board  of  Health  show  that  artificial  aeration  greatly 
increases  the  rate  of  purification  in  the  case  of  sewage  filtration.  But 
to  add  large  quantities  of  oxygen  to  water  that  already  contains  oxygen 
appears,  from  experiments  by  Drown  and  from  analyses  of  aerated 
water  in  various  places,  to  have  little  or  no  effect  on  the  organic  matter. 
Experiments  on  aeration  were  made  by  Down  \  in  several  ways : 
(i)  by  exposing  water  in  bottles  to  the  air  of  a  room  ;  (2)  by  drawing  a 
current  of  air  through  the  water ;  (3)  by  shaking  water  in  a  bottle  ;  and 
(4)  by  exposing  water  to  air  under  a  pressure  of  60  to  75  pounds  per 
square  inch.  The  results  of  some  of  the  experiments  are  given  in 
Table  No.  73.  The  variations  shown  in  the  amount  of  albuminoid 
ammonia  are  too  small  to  be  significant.  Other  experiments  on  very 
dilute  sewage  gave  about  the  same  results,  with  the  exception  that  a 
part  of  the  free  ammonia  was  removed  in  the  same  way  that  any  gas 
can  be  driven  out  by  aeration.  The  general  results  of  the  experiments 
are  confirmed  by  analyses  made  on  river-waters  at  points  above  and 
below  falls  or  rapids. 

*  Several  cities  in  India  have,  however,  installed  filter-plants  on  this  system, 
t  For   description    of   form   of  domestic   sand    filter   see  article  by    Fletcher; 
Eng.  News,  1906,  LVI.  p.  141. 

t  Mass.  Board  of  Health,  1891,  p.  385. 


AERA  TION. 


535 


TABLE  NO    73. 

RESULTS   OF   EXPERIMENTS    ON    AERATION    OF   COCHITUATE   WATER. 

(Parts  per  100,000.) 


Free 
Ammonia 

Albumi- 
noid 
Ammonia 

Nitrogen 
as 
Nitrites 

Nitrogen 
as 

Nitrates 

First  experiment: 
Original  sample     

.  0014 

.0182 

.  OOO2 

.  O2  7  C 

After  standing  in  open  bottle  for  48  hours     .    .    . 
After  aerating  by  current  of  air  for  48  hours     .    . 
After  standing  in  open  bottle  for  216  \  hours    .    . 
After   standing   49?    hours    and   then  aerating  by 

.0008 
.0014 
.0036 

0026 

.0176 
.0170 
.0158 

01  c6 

.0005 
.0003 
.OOO2 

OOO2 

.0250 
.0250 
.0250 

02  so 

Fourth  experiment: 
Original  sample                                               .            • 

0018 

0140 

.OOO2 

v^^v 

O2OO 

After  standing  for  72  hours                   .            ... 

.0016 

.  OI  <2 

.OOO2 

O^OO 

After  aerating   "     "        "         

.0024 

.O142 

.OOO2 

.O2OO 

After  being  under  pressure  of  75  Ibs.  for  72  hrs.  . 

.0036 

.0150 

.  000.2 

.0250 

Though  aeration  may  effect  little  or  no  change  in  the  organic 
matter  present  in  a  water,  it  does  have  a  very  important  action  in  the 
case  of  waters  from  ponds  and  reservoirs  which  possess  offensive  odors 
or  tastes  because  of  certain  dissolved  gases  present.  These  gases  may 
arise  either  through  the  putrefaction  of  dead  organic  matter,  such  as 
the  vegetation  left  in  a  reservoir  when  constructed,  or  the  dead  algae 
and  other  organisms  which  may  periodically  grow  in  the  water,  or  they 
may  be  formed  in  the  growth  of  certain  microscopical  organisms.  In 
any  case  aeration  is  very  effective  as  it  causes  the  displacement  of  the 
objectionable  gases  by  the  gases  of  the  atmosphere.  Where  waters  are 
to  be  filtered  that  are  deficient  in  oxygen  some  method  of  aeration 
should  be  employed.  Another  use  of  aeration  is  the  prevention  of  the 
growth  of  algae  in  small  reservoirs  by  the  agitation  produced  by  the  pro- 
cess. In  the  removal  of  iron  from  ground-waters  aeration  also  plays 
an  important  part  as  more  fully  described  in  Art.  565. 

Aeration  is  accomplished  in  various  ways.  It  may  be  done  by 
causing  the  water  to  flow  over  cascades  or  weirs,  or  to  fall  freely  from 
broad  areas  of  perforated  plates,  or  by  still  other  means.  The  more 
extensive  the  aeration  required  the  more  thorough  must  be  the  exposure 
to  the  air.  The  largest  plants  designed  especially  for  aeration  are 
probably  those  of  the  Spring  Valley  Water-works  of  San  Francisco. 
There  are  three  separate  plants,  all  of  similar  design.  The  one  known 
as  the  College  Hill  plant  has  a  capacity  of  8  million  gallons  per  day. 
The  water  rises  about  20  feet  in  an  upright  pipe,  is  then  conducted 


536 


MISCELLANEOUS  PURIFICATION  PROCESSES. 


through  two  long  wooden  flumes  and  distributed  from  these  through 
holes  in  the  sides,  to  a  series  of  wooden  platforms.  These  are  about 
3  feet  apart  vertically  and  are  made  of  i-in.  plank  6  inches  wide  laid 
\  inch  apart.  The  result  of  the  aeration  appears  in  this  case  to  be 
quite  marked,  according  to  the  report  of  the  Board  of  Health.  The 
results  are,  for  the  three  plants,  as  follows,  in  parts  per  100,000:  * 

Albuminoid  ammonia:  123 

Before  aeration    00620      .00756      .00756 

After  aeration 00416      .00252      .00492 

Oxidizable  organic  matter: 

Before  aeration    5.000        4.24          4.24 

After  aeration 1.665        2.94          1.80 

It  is  to  be  noted  that  the  albuminoid  ammonia  is  very  low  before 
treatment. 

At  Albany  aeration  is  accomplished  by  allowing  the  water  to  spray 
into  the  settling-reservoir  through  small  holes  in  the  vertical  inlet-pipes 
(see  Figs.  120,  121). 

A  more  effective  form  of  aerator  is  that  used  in  the  filter  plant  at 
Reading,  Pa.,  and  shown  in  Fig.  iSQb.  As  at  Albany  the  aerator  is 


Perforated  Plate 


FIG.  i39b.    AEKATOR  HEAD,  READING,  PA. 

attached  to  the  inlet  pipes  of  the  settling  reservoir.  The  water  flows 
over  the  enlarged  lip  of  the  vertical  outlet  pipe  and  falls  through  a 
large  horizontal  perforated  plate  into  the  reservoir. 

559.  Softening  of  Water.  —  Water  is  rendered  hard  by  the  presence 
of  lime  and  magnesia,  chiefly  in  the  form  of  carbonates  and  sulfates, 
but  occasionally  as  chlorids  and  nitrates.  The  carbonates  cause 
so-called  temporary  hardness  (removable  by  boiling),  while  the  sul- 
fates and  other  compounds  cause  permanent  hardness.  The  various 
objections  to  a  hard  water  have  been  fully  pointed  out  in  Chapter  IX 

*  Eng.  Record^  1896,  xxxiv.  p.  201 ;  1899,  XL.  p.  155. 


SOFTENING    OF   WATER. 


537 


(Art.  159),  but  it  may  be  well  to  repeat  here  the  most  important  facts. 
In  using  a  hard  water  for  washing  purposes  approximately  2  ounces  of 
soap  are  neutralized  or  wasted  for  each  100  gallons  of  water  for  each 
grain  per  gallon  of  calcium  carbonate  or  its  equivalent.  In  boiler  use 
the  carbonates  of  lime  and  magnesia  are  precipitated,  forming  a  deposit 
which  can  usually  be-  removed  by  blowing  out,  unless  accompanied  by 
scale-forming  substances.  Sulfate  of  lime  precipitates  at  high  tempera- 
tures and  forms  a  very  hard,  objectionable  scale,  particularly  if  the 
water  contains  other  suspended  matter.  The  solubility  of  the  sulfate 
is  approximately  given  by  the  following  table  : 


Temperature 
Fahr. 

Pressure, 
Lbs.  above  Atmospheric. 

Grains  per  Gallon, 
CaS04. 

32 

Ill 

68 

120 

104 

I25 

140 

121 

I76 

114 

212 

0 

III 

284 

37-8 

45 

324.S 

80.8 

33 

356.5 

132.0 

16 

473 

5I3-5 

10 

Of  the  other  substances  the  sulfate  of  magnesium  is  the  most 
common.  It  is  objectionable  as  tending  to  decompose  at  high  tem- 
peratures, forming  scale. 

560.  Chemistry  of  Water  Softening.  —  The  softening  of  water  is 
accomplished  by  simple  processes  of  chemical  precipitation.  To 
remove  the  carbonates,  lime  is  used  as  the  precipitant.  The  carbonates 
are  held  in  solution  chiefly  by  virtue  of  the  carbonic  acid  dissolved  in 
the  water,  and  on  adding  lime  the  acid  unites  with  it,  forming  carbonate 
of  lime.  In  the  case  of  hardness  due  to  the  carbonate  of  lime  the 
reaction  is 


CaCO3  +  CO2  +  Ca(OH)2  =  2CaCO 


H2O. 


The  resulting  carbonate  is  now  but  slightly  soluble  and  so  precipitates 
out.*  With  the  carbonate  of  magnesia,  a  similar  reaction  is  presumed 
to  first  take  place,  thus  : 

MgC03  +  C02  +  Ca(OH)2  =  MgCO,  +  CaCO,  +  HO; 


*  The  lime  may  also  be  considered  as  being  present  as  a  bicarbonate,  which 
changes  to  the  insoluble  carbonate  when  Ca(OH)2  is  added. 


5  38  MISCELLANEOUS  PURIFICA  TION  PROCESSES. 

but  as  the  carbonate  of  magnesia  is  quite  soluble,  a  further  quantity  of 
lime  is  required  to  complete  the  process,  thus  : 


MgC03  +  Ca(OH)2  =*  Mg(OH)2  +  CaCO 


,. 


The  hydrate  precipitates  out. 

To  remove  the  sulfates,  sodium  carbonate  (Na2CO3)  is  used.  Lime 
must  also  be  added  in  the  case  of  magnesium  sulfate.  The  reactions 
are: 

CaSO4  4-  Na2CO3  »  CaCO3  +  Na2SO4, 
and 


MgS04  +  Ca(OH)2  +  Na2C03  =  Mg(OH)2  +  CaCO3  +  Na2SO4. 

The  sodium  sulfate  resulting  from  these  reactions  is  very  soluble  and 
unobjectionable  in  the  amount  likely  to  be  present.  The  chlorids  and 
nitrates  may  be  removed  in  the  same  way  as  the  sulfates. 

561.  General  Features.  —  The  lime  process  for  the  removal  of  tem- 
porary hardness  was  invented  in  1841  by  Dr.  Clark  of  England,  and 
is  commonly  known  by  his  name.  It  has  been  used  quite  extensively 
in  that  country,  where  many  towns  are  supplied  with  water  drawn  from 
the  chalk  deposits.  Various  methods  of  carrying  out  the  details  of  the 
process,  relating  principally  to  the  application  of  the  lime  and  the 
removal  of  the  precipitate,  have  been  devised.  These  are  known  under 
various  names,  but  the  general  principle  is  the  same  in  all.  The 
lime  is  usually  added  in  the  form  of  lime-water,  although  milk  of 
lime  is  also  used.  When  both  permanent  and  temporary  hard- 
ness are  to  be  removed  it  is  necessary  to  add  both  lime  and  sodium 
carbonate. 

.  The  chief  features  of  a  softening  plant  relate,  to  the  apparatus  for 
preparing  and  introducing  the  chemical,  the  sedimentation  basins  for 
the  removal  of  the  main  body  of  the  precipitate  and  the  final  filtration 
or  clarification  of  the  settled  water.  The  lime  water  is  usually  prepared 
as  a  standard  saturated  solution.  After  it  is  introduced  the  mixing  is 
accomplished  and  the  chemical  action  hastened  by  agitation  of  the 
water  either  by  passing  it  rapidly  through  baffled  channels  or  by  means 
of  steam  or  compressed  air  or  by  mechanical  devices.  This  agitation 
also  assists  in  subsequent  precipitation  of  the  finer  particles  by  means 
of  the  coagulating  action  of  the  larger  particles.  The  precipitation  is 
carried  out  in  ordinary  settling  basins,  after  which  the  partially  cleared 
water  is  usually  filtered  through  some  form  of  rapid  filter.  For  this 
purpose  cloth  filter  presses  are  often  used,  while  in  some  of  the  largest 
modern  plants  the  ordinary  rapid  sand  filter  is  employed.  Traces  of 


SOFTENING  OF  WATER.  539 

free  alkali  which  may  remain  in  the  softened  water  may  be  removed  by 
adding  CO2,  or  by  mixing  in  a  small  proportion  of  the  untreated 
hard  water. 

In  the  original  Clark  process  the  precipitate  was  removed  by  sub- 
sidence in  large  tanks.  In  the  Porter-Clark  process  (one  of  the  most 
commonly  used  processes)  the  water,  after  the  application  of  the  lime, 
rises  slowly  through  an  iron  cylinder  containing  broad  shelves  on  which 
the  precipitate  settles,  and  from  which  it  is  scraped  at  intervals  by 
means  of  a  series  of  paddles.  The  final  cleaning  takes  place  in 
settling-basins. 

In  the  Archbutt-Deeley  Process,  used  in  several  modern  English 
plants,  the  precipitation  is  aided  by  stirring  up  for  several  minutes 
some  of  the  previously  accumulated  sediment.  After  sedimentation  the 
small  amount  of  CaCO3  remaining  in  suspension  is  redissolved  and  all 
free  alkali  removed  by  adding  CO2  obtained  from  a  small  coke  stove. 
This  recarbonizing  also  renders  the  water  more  palatable. 

562.  Examples  of  Softening  Plants.  —  One  of  the  largest  softening 
plants  yet  constructed  is  that  at  Southampton,  England,  where  the  entire  city 
supply  is  softened  to  the  extent  of  reducing  the  hardness  from  18°,  Clark 
scale,*  to  about  6°.  The  capacity  of  the  plant  was,  in  1892,  2,400,000 
gallons  per  day.  The  lime  is  burnt  in  a  kiln  near  at  hand.  The  slaked  lime 
is  dissolved  in  the  softened  water  in  two  large  cylinders,  the  amount  taken  in 
solution  being  about  75  grains  per  gallon.  At  this  ratio  it  requires  for  this 
plant  about  one-tenth  as  much  lime-water  as  the  amount  of  water  to  be 
treated.  After  receiving  the  chemical,  the  water  passes  into  a  large  cistern, 
where  much  of  the  precipitate  settles ;  the  finer  particles  are  removed  by  a 
series  of  Atkin  filters.  These  filters  consist  of  perforated  zinc  disks  covered 
with  filter-cloths  and  arranged  in  pairs  along  a  hollow  shaft.  They  are  immersed 
in  the  water  to  be  filtered.  The  water  passes  through  these  disks  to  the 
space  between  them  and  thence  through  the  hollow  shaft  to  the  outlet.  The 
filters  are  cleaned  every  6  or  7  hours  by  spraying  them  from  fixed  perforated 
pipes,  the  disks  and  shaft  being  rotated  at  the  same  time. 

The  cost  of  the  plant  is  stated  to  be  about  $48,000,  which  is  equivalent 
to  $20,000  per  million  gallons  capacity.  The  cost  of  operation  is  about  $4 
per  million  gallons,  t 

At  Columbus,  Ohio,  a  softening  plant  with  a  daily  capacity  of  30,000,000 
gallons  is  being  constructed  (1908).  Lime-water  and  a  solution  of  soda  ash 
will  be  used  to  eliminate  the  carbonates  and  sulfates.  Rapid  filters  are 
used  to  remove  the  precipitate  from  the  softening  process,  and  during  times 
of  high  turbidity  of  the  raw  water  the  relatively  large  amounts  of  gelatinous 
hydrate  of  magnesia  will  act  as  a  coagulant.  Arrangements  are  provided  to 
by-pass  raw  water  into  the  softened  water,  in  order  to  eliminate  any  traces  of 
caustic  alkalinity  which,  if  permitted  to  remain,  would  cause  a  hard  precipitate 

*  i°  =  i  grain  of  carbonate  per  Imperial  gallon  =  i  part  in  70,000. 

t  Proc.  Inst.  C.  E.,  1891-92,  cvm.  p.  285  ;  Eng.  News,  April  16,  1892,  p.  380. 


540  MISCELLANEOUS  PURIFICATION  PROCESSES. 

in  the  pipes.  When  required,  sulfate  of  iron  or  alumina,  can  be  added  as  an 
additional  coagulant  to  remove  excessive  turbidity.  The  lime-water  is  pre- 
pared by  introducing  10  per  cent  milk  of  lime  into  the  desired  amount  of 
raw  water  which  is  then  conveyed  to  the  bottom  of  the  mixing  tank  where 
it  is  stirred  mechanically.  It  gradually  rises  in  this  tank,  clearing  as  it  rises, 
and  is  drawn  off  at  the  top  as  lime  water.  Weirs  and  Venturi  meters  are  used 
for  measuring  purposes.* 

Other  municipal  plants  worthy  of  note  are  those  at  Oberlin,  O.,  and 
Winnipeg,  Canada. f 

563.  Softening  of  Water  for  Boiler  Use.  —  In    Europe,  plants   for 
the  softening  of  boiler  feed-water  have  been  in  general  use  for  many 
years  and  recently  many  such  plants  have  been  installed  by  railroad 
companies  in  this  country.     The  operation  of  these  plants  has  resulted 
in  a  great   economy  in    locomotive    maintenance.     In    some  of   these 
plants   the   precipitate  is  removed   by  the  use  of   settling-tanks  alone 
but  generally  some  form  of  rapid  filter  is  used.    The  chemicals  used  are 
lime  and  usually  soda  ash,  or  crude  sodium  carbonate.f 

Many  scale  preventives  have  been  proposed  for  use  in  boilers,  but 
probably  the  best  in  general  use  is  sodium  carbonate.  This  breaks  up 
the  sulfates  as  previously  shown,  and  thus  prevents  the  formation  of  a 
hard  deposit ;  but  the  precipitation  of  the  carbonates  is  increased  by 
the  process.  The  sodium  sulfate  remains  in  solution,  but  should  not 
be  allowed  to  concentrate  too  greatly  or  it  will  cause  foaming. 

564.  Bacterial  Efficiency  of  the  Softening  Process.  —  Experiments 
by  Frankland,  and  results  of  operation  in  practice,  show  a  considerable 
degree  of  bacterial  purification  in  the  softening  process,  —  in  some  cases 
quite  as  high  as  that  of  other  processes.     The  lime  precipitate  is  pul- 
verulent instead  of  gelatinous  in  character,  and  experiments  at  Louis- 
ville  showed   the  process  to  be  in  general  quite   inadequate  for  the 
removal  of   bacteria,  unless  lime  be  introduced  in  considerable  excess 
(Art.  475).     Where  water  contains  magnesia,  as  at  Columbus,  the  pre- 
cipitate acts  effectively  as  a  coagulant,  and  by  the  use  of  rapid  filters 
the  bacterial  effiiency  should  be  very  good. 

565.  Removal  of  Iron  from  Waters.  —  Cause  of  Iron  in  Waters.  — 
Ground-waters   may  not   infrequently  contain  iron  in  solution  and    so 
have  their  taste  and  appearance  impaired.      Such  waters  are  apt  to  act 
as  astringents.     Where  iron  is  present  in  the  proportion  of  0.4-0.5  part 
per  million,  little  or  no  trouble  from  taste  or  appearance  is  to  be  noted. 
An  excess  of  iron,  however,  is  not  only  disagreeable  to  the  taste,  but 
is  objectionable  for  domestic  use,  especially  in  the  laundry. 

*  Eng.  Record,  1906,  LIII.  p.  202. 
t  See  references  at  end  of  chapter. 


REMO  VAL  OF  IRON  FROM  WA  TERS.  541 

The  presence  of  iron  in  ground-waters  is  due  to  a  series  of  chemical 
changes  that  are  induced  by  the  presence  of  organic  matter.  Most 
soils,  as  sands,  gravel,  etc.,  contain  more  or  less  iron,  which  is  generally 
in  the  form  of  ferric  oxid  (Fe2O3).  As  surface-waters  percolate  into 
soil-layers  containing  organic  matter,  they  are  rapidly  deprived,  by  the 
oxidation  of  the  organic  matter,  of  the  free  oxygen  which  they  contain. 
When  this  supply  of  oxygen  is  used  up,  the  organic  matter  attacks  the 
insoluble  ferric  oxid,  reducing  it  to  ferrous  oxid  (FeO),  which  unites 
with  the  carbonic  acid  naturally  present  in  the  water,  thus  forming 
ferrous  carbonate  (FeCO3),  which  is  soluble  in  waters  of  an  acid  reac- 
tion. Therefore,  wherever  the  conditions  in  the  soil  favor  these  chem- 
ical changes,  iron  may  appear  in  the  water.  In  alluvial  plains,  river 
valleys,  and  similar  locations,  where  organic  matter  is  more  or  less 
abundant,  waters  of  this  class  are  often  found.  In  a  number  of  differ- 
ent cities  along  the  Atlantic  seaboard,  as  on  Cape  Cod,  Long  Island, 
and  the  Jersey  shore,  as  well  as  in  numerous,  locations  in  the  alluvial 
plains  of  Germany,  Holland,  and  Denmark,  trouble  from  such  a  source 
has  been  experienced. 

In  such  waters,  the  iron  bacterium,  Crenothrix>  is  very  likely  to 
grow.  As  this  form  develops  in  darkness,  it  is  capable  of  multiplying 
in  distributing-pipes,  where  it  may  sometimes  accumulate  to  such  an 
extent  as  to  seriously  interfere  with  the  service.  This  organism  lives 
on  the  soluble  iron,  utilizing  it  as  a  food,  finally  precipitating  it  as 
ferric  oxid  in  its  gelatinous  sheath,  and  so  causing  the  accumulation  of 
flocculent  masses.  Upon  the  death  and  decay  of  these  organisms,  bad 
odors  and  unpleasant  tastes  may  be  produced. 

Waters  containing  these  iron  salts  are  clear  when  first  drawn,  but 
soon  become  cloudy  on  standing,  due  to  the  absorption  of  oxygen  from 
air  and  the  consequent  conversion  of  the  soluble  ferrous  salt  into  ferric 
hydroxid.  This  material  in  time  settles  out  as  a  rusty  precipitate. 
Sometimes  where  there  is  an  abundance  of  organic  matter  in  solution, 
as  in  waters  from  peaty  sources,  soluble  compounds  are  formed 
with  the  organic  matter  that  are  not  readily  oxidized  upon  exposure 
to  air. 

566.  Treatment  of  Iron  Waters.  —  It  has  been  noted  that  in  many 
cases  where  the  iron  is  present  as  ferrous  carbonate  it  will  be  removed 
by  oxidation  if  exposed  to  the  air.  This  reaction  is  utilized  in  the 
practical  treatment  of  such  waters,  and  in  most  of  the  plants  installed 
for  the  removal  of  iron  from  ground-waters  aeration  is  employed 
to  facilitate  this  oxidation.  The  precipitated  iron  (Fe2O3)  is  generally 
removed  from  the  water  by  filtration  through  sand.  As  a  heavy 


542  MISCELLANEOUS  PURIFICATION  PROCESSES. 

flocculent  deposit  is  produced  that  does  not  readily  penetrate  the  filter, 
even  where  coarse  sand  is  employed,  rapid  filtration  is  possible. 

To  satisfactorily  treat  waters  of  this  class,  it  is  necessary  to  reduce 
the  iron  content  to  less  than  0.5  part  per  million.  The  percentage  of 
iron  removed,  therefore,  is  not  of  so  much  value  as  a  determination  of 
the  content  of  the  effluent. 

The  extent  of  aeration  required  varies  considerably,  according  to 
the  character  of  the  water,  and  the  conditions  necessary  for  successful 
treatment  cannot  in  all  cases  be  determined  without  experiment.  In 
some  cases  simple  exposure  in  open  canals  gives  sufficient  aeration,  or 
the  mere  spraying  in  small  jets,  or  other  simple  means  may  be  success- 
ful. At  Chariot tenberg,  and  several  other  places  in  Germany,  the 
water  is  passed  through  aerators  made  of  coarse  pieces  of  coke.  At 
Beelitzhof  the  aerators  are  made  of  blocks  of  stone,  and  appear  to  work 
equally  well.  At  Provincetown,  Mass.,  Mr.  H.  W.  Clark  found  that 
where  simple  aeration  would  not  answer,  a  coke-filter  was  successful, 
due,  it  was  thought,  to  some  chemical  action  of  the  coke. 

In  some  cases  the  difficulty  of  aeration  is  probably  due  to  excess  of 
organic  and  of  free  carbonic  acid.  At  Reading,  Mass.,  lime  and  sul- 
fate  of  alumina  have  been  successfully  used  in  connection  with  aeration 
and  filtration.  This  process,  however,  increases  the  hardness  very 
considerably.  Recent  experiments  by  Mr.  R.  S.  Weston  indicate  that 
good  results  can  be  secured  by  the  addition  of  ferric  hydrate  electrically 
produced.  At  Provincetown,  Mr.  Clark  found  that  ferrous  sulfate  or 
ferric  chlorid  would  precipitate  the  iron. 

567.  Application  of  Electricity  to  Water  Purification.  —  Electricity  is 
indirectly  applicable  to  the  purification  of  water  in  two  ways  :  (i)  the 
electrolytic  production  of  a  disinfectant  and  deodorizer ;  (2)  the  elec- 
trolytic production  of  a  coagulant.  In  both  of  these  cases  it  appears 
that  the  action  of  the  substance  produced  is  quite  the  same  as  when 
produced  in  other  ways,  and  the  question  is  primarily  one  of  the  eco- 
nomical manufacture  of  the  substance  in  question. 

The  principal  method  of  producing  t'ic  first-named  class  of  com- 
pounds is  by  the  electrolysis  of  salt-water  or  sea-water,  producing  thereby 
principally  the  hypochlorite  of  sodium,  a  powerful  disinfectant.  Elec- 
tricity has  also  more  recently  been  employed  in  the  production  of  ozone. 
The  action  of  substances  of  this  character  is  discussed  in  Art.  570.  The 
process  is  one  which  has  so  far  been  chiefly  limited  to  sewage  treatment, 
but  under  certain  conditions  may  prove  of  value  in  water  purification. 

The  other  general  method  has  been  applied  to  the  production  of 
hydrate  of  iron  and  hydrate  of  alumina  with  results  comparable  with 


THE  ANDERSON  REVOLVING  PURIFIER.  543 

the  use  of  those  substances  as  already  described.  This  subject  was 
thoroughly  investigated  by  Mr.  Fuller  at  Louisville,  with  the  conclu- 
sion *  that  aluminum  cannot  be  economically  used  in  this  way  on 
account  of  its  excessive  cost.  Aluminum  in  the  sulfate  is  much 
cheaper  per  pound  than  the  metallic  aluminum. 

Regarding  ferric  hydrate,  Fuller  states  that  "  under  practical  con- 
ditions this  process  (electrolytic)  can  be  used  to  produce  ferric  hydrate, 
a  good  coagulant,  up  to  the  point  where  the  atmospheric  oxygen  dis- 
solved in  the  water  is  not  completely  exhausted."  Since  the  more 
recent  development  of  the  use  of  sulfate  of  iron  with  lime  the  cost  of 
the  electrolytic  process  will,  however,  rarely  compare  favorably. 

A  very  considerable  advantage  of  the  electrolytic  production  of  the 
coagulant  is  that  it  does  not  add  any  objectionable  substance  to  the 
water,  or  increase  its  hardness. 

568.  The  Anderson  Revolving  Purifier. — This  process  of  purification 
(patented)  is  in  reality  a  method  of  adding  iron  as  a  coagulant  previous 
to  subsidence  and  filtration.     The  water  is  passed  through  a  revolving 
cylinder,   containing  a  quantity  of    iron   in   the  form  of   turnings   or 
punchings,   which,   as    the    cylinder   rotates,   are   lifted   and   scattered 
through  the  water  by  means  of  projections  bolted  on  the  inside  of  the 
cylinder.     The  inlet  and  outlet  are  through  hollow  trunnions  on  which 
the  cylinder  rotates.     The  rate  of  flow   is   such  as  to  give  the  water 
3  to  5  minutes  contact  with  the  iron.     The  result  of  the  operation  is 
that  a  small  amount  of  the  iron  is  dissolved  by  the  carbonic  acid  of  the 
water,  forming  ferrous  carbonate.     On  exposure  of  the  water  to  the  air 
in    reservoirs,   or   by  artificial  aeration,   this   is   oxidized  into  hydrate 
which  acts  as  a  coagulant  similarly  to  aluminum  hydrate,  in  removing 
color  and  in  aiding  sedimentation  and  filtration   (see   Chapter  XXI). 
This  system  is  in  use  at  a  number  of  places  in  Europe,  notably  at 
Antwerp,  Dordrecht,  and  for  some  of  the  suburban  supplies  of  Paris. 
After  treatment  the  water  is   filtered  at  a  moderate  rate  through  sand 
filters. 

569.  Sterilization  and  Distillation. — Not  infrequently  a  public  supply 
becomes  suspicious  and  the  prudent  consumer  is  forced  to  protect  his 
household  by  private  means.     Generally  speaking,  the  introduction  of 
satisfactory  filters  will  insure  safety  if  the  same  are  properly  managed. 
Another  method  on  which  even  greater  reliance  can  be  placed  is  the 
use  of  heat.     There  are  no  pathogenic  bacteria  that  are  liable  to  be 
distributed  by  the  way  of  the  water-supply  that  are  able  to  withstand 

*  Fuller.    Water  Purification  at  Louisville. 


544  MISCELLANEOUS  PURIFICATION  PROCESSES. 

the  influence  of  boiling  water  for  a  period  exceeding  10-15  minutes. 
Cholera  and  typhoid  succumb  in  5  minutes  or  less.  In  case  of  sudden 
outbreaks  of  disease  or  temporary  disturbance  of  installed  water-sup- 
plies, this  method  can  always  be  relied  on  with  perfect  safety. 
There  are  several  types  of  sterilizers  that  have  been  placed  on  the 
market  that  are  adapted  to  individual  use  (see  literature) ;  also  appa- 
ratus that  is  designed  for  the  treatment  of  large  quantities  that  would 
be  of  service  in  case  of  epidemics.  Ordinarily,  measures  of  this  sort 
are  left  to  the  option  of  the  water-consumer,  but  in  times  of  extensive 
epidemics,  as  in  the  Hamburg  cholera  outbreak  of  1 893,  public  stations 
supplying  sterilized  water  may  be  established.  Boiling  does  not,  how- 
ever, render  potable  a  water  containing  large  amounts  of  organic 
matter,  although  it  may  destroy  the  disease-germs  that  may  be  therein. 
By  distillation  a  water  can  be  obtained  free  from  dissolved  matter  as 
well  as  bacteria. .  This  process  is  extensively  used  on  shipboard  to 
obtain  potable  water  from  sea-water,  and  in  a  few  places  on  the  sea- 
coast  for  similar  purposes.  In  a  recent  test  of  a  ""triple-effect "  evap- 
orator at  the  Dry  Tortugas,  Fla.,  a  net  distillation  of  13.98  pounds  of 
water  per  pound  of  coal  was  obtained.*  Distilled  water  is  rendered 
more  palatable  by  aeration  and  the  introduction  of  a  small  quantity 
of  salt. 

570.  Purification  by  Addition  of  Chemicals.  —  Chemical  substances, 
such  as  alum  and  iron  sulfate,  are  frequently  added  to  water  to  aid  in  its 
purification,  but  the  object  of  these  is  to  cause  flocculation,   and  the 
bacteria  are  removed  by  subsidence  or  filtration  rather  than  destroyed. 
In    the    main,    chemical    substances    that  are    sufficiently  powerful  to 
destroy  organisms  in  water  are  likely  to  injure  the  potable  quality  of 
waters,  unless  they  can  be  later  removed  or  neutralized. 

571.  Ozone. — Apparently   one    of   the   most    successful    of   these 
methods  is  in  the  use  of  ozone  which  has  already  been  applied  on  a 
commercial    scale.      The   gas    is    generated    electrolytically   and    then 
passed   through  the  water.     Experiments   made  by  Weyl  f    on   river- 
water  such  as  the  Spree,  which  contained  from  16,000-18,000  bacteria 
per  c.c.,  showed  a  reduction  to  100-200  organisms  per  c.c.     The  water 
is  pumped  into  a  tower  and  allowed  to  flow  slowly  over  stones,  thus 
bringing  it  in  contact  with  the  air  that  is  heavily  charged  with  ozone. 
The  gas    acts  as  a  powerful    disinfectant,   destroying   the  pathogenic 
organisms    with    certainty.      It    is    not  very  readily   absorbed    by  the 
water,  hence  water  treated  in  this  way  does  not  act  easily  on  pipes. 

*  Eng.  News,  1900,  XLIII.  p.  203. 

t  71.    Versammlung  deutscher  Naturforscher  u.  Aerzte,  1899. 


PURIFICA  TION  B  Y  ADDITION  OF  CHEMICALS.  545 

Recently  experiments  were  tried  at  Lille,  Belgium,  with  the 
apparatus  of  Marmier  and  Abraham.  Calmette,*  reporting  these 
results,  says  that  its  efficiency  is  higher  than  any  other  known  process. 
All  pathogenic  and  other  bacteria,  with  the  exception  of  a  few  harm- 
less spore-bearing  hay  bacilli,  were  destroyed.  The  ozonization  of  the 
water  adds  no  element  prejudicial  to  health. 

Experiments  made  in  1904,  by  a  special  committee  of  investigation, 
on  a  plant  installed  at  the  Saint-Maur  water-works,  Paris,  showed  a 
bacterial  efficiency  above  99  per  cent,  the  bacteria  remaining  in  the 
water  consisting  only  of  harmless  varieties. 

For  the  successful  working  of  an  ozone  sterilizing  plant  it  is  neces- 
sary that  most  waters  be  filtered  before  being  ozoned.  As  most  waters 
can  be  made  satisfactory  by  filtration,  the  additional  cost  of  the  ozone 
process  in  order  to  secure  even  complete  sterilization  will  seldom  be 
justified.  It  is  a  method  which  may  prove  of  value  in  special  cases, 
but  it  is  too  expensive  for  ordinary  use.  It  may  also  be  said  that  it 
is  hardly  out  of  the  experimental  stage  and  that  absolute  sterility  is 
very  difficult  to  obtain,  f 

572.  Chlorinated  Lime  (Traubc's  Method).  — In  1893  Traube  \  pro- 
posed an  exceedingly  simple  and  efficient  method  of  rendering  water 
germ-free  by  the  addition  of  chlorinated  lime  or  bleaching-powder 
(CaOCl2).  This  strong  disinfectant  consists  of  a  mixture  of  calcium 
hydroxid,  Ca(OH)2,  calcium  chlorid,  CaCl2,  and  calcium  hypochlorite, 
Ca(ClO)2.  By  virtue  of  the  active  chlorine  which  it  contains  it  will 
destroy  all  bacteria  in  a  few  hours  even  in  extremely  dilute  solutions. 
The  excess  of  the  chlorinated  lime  may  be  readily  neutralized  by  the 
addition  of  sodium  sulfite  or  calcium  bisulfite.  Water  so  treated  is 
perfectly  harmless,  and  does  not  have  its  taste  or  appearance  impaired ; 
in  fact,  remains  unchanged  except  for  a  slight  increase  in  hardness. 

Other  methods  of  utilizing  the  strong  disinfecting  action  of  chlorine 
have  been  tried  with  some  success.  At  Ostend,  successful  experiments 
have  been  made  with  a  process  in  which  a  compound  of  chlorine  and 
oxygen  has  been  used.  Chlorid  of  lime  with  chlorid  of  iron  is  used 
in  the  so-called  "  ferro-chlore  "  process.  This  process  has  been  shown 
to  give  satisfactory  results  in  experiments  in  Belgium  and  also  at 
Paris.  § 

*  Rev.  Set.,  4  Ser.  xi.  p.  432. 

t  See  report  on  use  of  Ozone  for  the  Croton  Water-supply.  Eng.  News,  1907 , 
LVIII.  p.  561. 

\  Zeit.f.  Hyg.,  1894,  xvi.  p.  149. 
§  Eng.  Record,  1906,  LIV.  p.  94. 


546  MISCELLANEOUS  PURIFICATION  PROCESSES. 

572a.  Peroxide  of  Hydrogen  (H2O2).  —  This  disinfecting  agent  can 
also  be  utilized  in  the  sterilization  of  water.  In  solutions  of  I  :  10,000 
the  cholera  organism  is  killed  in  five  minutes ;  the  typhoid  bacillus  in 
one  day  in  solutions  of  double  this  strength.  In  proportions  of  I  :  1000, 
water  is  rendered  practically  germ-free  within  24  hours,  and  these  pro- 
portions do  not  affect  the  taste. 

572b.  Copper  Stdfate.  —  The  action  of  copper  sulfate  as  a  germicide 
is  well  known  and  its  use  for  this  purpose  has  been  more  or  less 
studied,  but  it  has  been  generally  objected  to  on  account  of  its  possible 
deleterious  effect  on  the  human  system.  Its  use  to  destroy  and  prevent 
the  growth  of  objectionable  algae  and  other  microscopical  organisms 
in  reservoirs  is  of  much  more  importance  and  has  been  successfully 
applied  in  many  cases. 

Attention  was  directed  to  the  highly  toxic  effect  of  copper  sulfate 
upon  algae  by  the  studies  of  Messrs.  Moore  and  Kellerman  in  the 
laboratory  of  Plant  Physiology  in  the  U.  S.  Department  of  Agriculture, 
published  in  1904.*  From  these  and  other  studies,  and  from  actual 
experience  in  practice,  it  is  found  that  an  amount  of  copper  sulfate 
of  i  part  in  2,000,000  is  sufficient  to  destroy  most  of  the  objectionable 
forms  of  organisms,  some  being  rapidly  destroyed  with  an  application 
of  only  i  part  in  20,000,000.  In  these  minute  quantities  no  harmful 
effect  can  arise  from  its  use  in  a  drinking  water,  and  considering  that 
very  few  applications  are  needed  during  the  season  and  that  a  large 
portion  of  the  copper  is  precipitated  with  the  organisms,  there  would 
seem  to  be  no  objection  to  its  use  under  proper  supervision.  The 
method  of  application  which  has  been  frequently  employed  is  to  drag 
sacks  containing  the  copper  sulfate  back  and  forth  through  the  reser- 
voir or  pond  in  a  more  or  less  systematic  manner.  With  careful  manip- 
ulation this  method  will  serve  to  distribute  satisfactorily  the  desired 
amount  of  material,  but  at  the  best  it  would  appear  that  some  form 
of  spray  apparatus  using  a  definite  solution  would  be  more  satisfactory. 

The  use  of  copper  sulphate  as  an  algicide  has  been  applied  in  many 
cases  with  good  results.  At  Butte,  Mont.,  a  reservoir  of  180,000,000  gal- 
lons was  given  two  treatments  at  a  cost  of  23  cents  per  million  gallons. 
An  amount  of  copper  sulfate  equivalent  to  i  part  in  8,000,000 
was  sufficient  to  destroy  the  asterionella  and  anabaena  which 
caused  the  trouble.  At  Hanover,  N.  H.,  a  reservoir  of  100,000,000 
gallons  received  a  single  treatment,  using  a  proportion  of  i  part  in 
4,000,000.  The  number  of  micro-organisms  was  decreased  in  24 
hours  from  600  per  c.c.  to  60  and  wholly  eliminated  in  60  hours. f 

*  Bulletin  No.  64,  Bureau  Plant  Ind.         t  See  references  on  p.  549. 


PURIFICATION  BY  ADDITION  OF  CHEMICALS.  547 

The  germicidal  effect  of  copper  is  well  established,  but  in  general 
it  is  not  effective  within  limits  that  would  be  permissible.  A  promising 
method  of  using  it  for  this  purpose  is  in  connection  with  iron  and  lime  as 
a  coagulant  in  rapid  filtration.  Tests  at  Marietta,  O.,  in  which  a  com- 
bined sulfate  of  iron  and  copper  was  used  containing  only  i  per  cent 
of  copper  sulfate,  showed  very  good  results.  The  average  of  eleven 
runs  gave  an  effluent  containing  but  12  bacteria  per  c.c.,  the  number 
in  the  river  water  being  1913.* 


LITERATURE. 

SPECIAL    FORMS    OF    FILTERS. 

1.  Filtering  Plant.     "  System    Fischer  und    Peters,"   at  Worms,  Germany. 

Eng.  News,  1892,  xxvni.  p.  231. 

2.  Schofer.     Sandstone-slab  Filters  on  the  Fischer  System  at  Worms.     Proc. 

Inst.  C.  E.,  1895-96,  cxxv.  p.  468. 

3.  Artificial  Sandstone  Filters.     Eng.  Record,  1897,  xxxv.  p.  515. 

4.  The    Arad    Water  Works    and  Fischer    Plate    Filters.      Engng.,    1901, 

LXXI.  p.  204.     Plate  filters  used.     Eng.  Record,  1902,  XLVI.  p.  296. 

5.  Maignen.    Scrubbers  for  Preparing  Water  for  Filtration.     Eng.  Record, 

1902,  XLVI.  p.  76. 

6.  Hering  and  Fuller.     The  Maignen  Preliminary  Filters  for  the  Prepara- 

tion of  Water  for  Sand  Filtration.     Abstract  of  Report,  Eng.  Record, 
1902,  XLVI.  p.  484. 

7.  Maignen.     The  Lower  Roxborough  Preliminary  Filters.     Proc.  Eng.  Club 

Phil.,  1904,  xxi.  p.  227. 

8.  Water    Purification    at    South    Bethlehem,    Pa.     Describes    Scrubbers. 

Eng.  Record,  1905,  LII.  p.  61. 

AERATION. 

1.  Drown.     The  Effect  of  the  Aeration  of  Natural  Waters.     Report  Mass. 

Bd.  Health,  1891,  p.  385  ;  Eng.  News,  1892,  xxvm.  p.  183. 

2.  Brush.     Aeration  of  a  Gravity  Supply.     Proc.  Am.  W.  W.  Assn.,  1891, 

P-  73- 

3.  Aeration  of  Charleston,  S.  C.,  Water-supply.     Eng.  Record,  1892,  xxvi. 

p.  197. 

4    Aeration   and  Continuous  Sand  Filtration  at  Ilion,  N.  Y.     Eng.  News, 
1894,  xxxi.  p.  466. 

5.  The  San  Francisco  Aerating-plant.     Eng.  Record,  1896,  xxxiv.  p.  201. 

6.  Metcalf .     Aerator  for  Mechanical  Filters  at  Winchester,     Ky.  Eng.  Newst 

1901,  XLV.  p.  410. 

7     The    Antietam    Filters  of    the  Reading,  W.  W.    Eng.  Record,  1905,  LI. 
p.  340. 

*  Eng.  Record,  1906,  LIII.  p.  392. 


548  MISCELLANEOUS  PURIFICATION  PROCESSES. 


SOFTENING. 

1.  Latham.     Softening  of  Water.     Paper  before  Soc.  of  Arts.     Of  historical 

value.     Eng.  News,  1885,  XIIL  p.  65. 

2.  Matthews.     The  Southampton  Water-works  and  Softening  Plant.     Proc. 

Inst.  C.  E.,  1891-92,  cvm.  p.  285. 

3.  Atkins.     Water  Softening  and  Scientific  Filtration.     London,  1894. 

4.  Collet.     Water  Softening  and  Purification.     London,  1895. 

5.  Archbutt.     Water  Softening.     Proc.  Inst.  M.  E.,  1898,  p.  404.     Abstract, 

Eng.  News,  1898,  XL.  p.  403 ;  Eng.  Record,  1898,  xxxvm.  p.  388. 

6.  Recent  Practice  in   Purifying  Feed-water  for  Locomotives.     Report  of 

Com.  of  Mast.  Mech.  Assn.     Eng.  News,  1899,  XLI.  p.  411. 

7.  The  Municipal  Water  Softening  Plant  at  Winnipeg.     Eng.  Record,  1902, 

XLV.  p.  555. 

8.  Molyneaux.     Water  Softening  Plant  at  the  Wilmslow  (Stockport)  Works. 

Jour.  Gas  Lgt.,  1902,  LXXX.  p.  1692. 

9.  The   Kennicott  Water  Softening  System.     Eng.  News,   1902,  XLVH.  p. 

386. 

10.  Four  Systems  of  Softening  Water  for  Industrial  Purposes.     Eng.  News, 

1903,  L.  p.  5. 

11.  The  Burt  Continuous  WTater  Softening  Process.     Eng.  News,  1904,  in. 

p.  238. 

12.  Railway  Water  Service.     Report  of  Com.  of  Am.  R'y.  Eng.  &  M.  of  W. 

Assn,  1905.     Eng.  News,  1905,  LIII.  p.  332. 

13.  The  Water  Softening  Plant  at  Oberlin,  O.     Eng.  News,   1905,  LIV.  p. 

313- 

14.  The   Water  Filtering  and   Softening  Works   at  Columbus,  Ohio.     Eng. 

Record,  1906,  LIII.  p.  202. 

REMOVAL    OF    IRON. 

1.  Wellmann.     Ueber  Beseitigung  des  Eisengehaltes  irn  Grundwasser  mit 

Beziehung  auf  die  Charlottenburger  Wasserwerke.     Jour.  f.  Gas.  u. 
Wasservers.,  1894,  xxxvn.  p.  595  ;  Eng.  News,  1895,  xxxiv.  p.  147- 

2.  Pippig.     Die  Grundwasser-Enteisenungsanlage  des  Kieler  Wasserwerks. 

Jour.  f.  Gas.  u.  Wasservers.,  1896,  xxxix.  p.  650- 

3.  Removal  of   Iron  from  Ground-water   at    Reading,  Mass.     Eng.  News, 

1896,  xxxvi.  p.  348. 

4.  Clark.     Removal  of  Iron  from  Ground-waters.     Jour.  New  Eng.  W.  W. 

Assn.,  1897,  xi.  p.  277. 

5.  Bancroft.     The  Iron-removal  Plant  at  Reading,  Mass.     Jour.  New  Eng. 

W.  W.  Assn.,  1897,  xi.  p.  294. 

6.  The   Removal   of    Iron   from   Ground-water.     Eng.   Record,    1899,   XL. 

p.  412.     Describes  several  plants. 

7.  Iron  Removal  from  Ground-water  at  Far  Rockaway  by  Slow  Sand  Filtra- 

tion.    Eng.  News,  1900,  XLIII.  p.  238. 

8.  Uber  d.  Grundwasser  von  Kiel  mit  besonderer  Beriicksichtigung  seines 

Eisengehaltes   u.  uber   Versuche    z.  Entfernung  d.  Eisens.     Zeit.  f. 
Hyg.,  xin.  p.  251. 

9.  Uber  die  Natur  und  Behandlung  eisenhaltigen  Grundwassers.     Zeit.  f. 

Hyg.,  xxn.  p.  68. 


LITER  A  TURE.  5  49 

10.  Iron    Removal   from   the    Prenzlau   Water-supply.      Eng.  Record,   1900, 

XLII.  p.  566. 

11.  Chase.    Removal  of  Iron  from  the  Water-supply  of  Superior,  Wis.     Eng. 

News,  1901,  XLV.  p.  141. 

12.  The  Removal  of    Iron  from  the  Water-supply  of  Reading,  Mass.     Eng. 

Record,  1906,  LIV.  p.  60 1. 

THE    ANDERSON    PROCESS. 

1.  Anderson.     The    Antwerp    Water-works.     Proc.    Inst.    C.    E.,   1882-83, 

cxxii.  p.  24. 

2.  Anderson.     The  Purification  of  Water  by  Means  of  Iron  on  the  Large 

Scale.     Proc.  Inst.  C.  E.,  1884-85,  LXXXI.  p.  279. 

3.  Ogston.     The  Purification  of  Water  by  Metallic  Iron  in  Mr.  Anderson's 

Revolving  Purifiers.     Proc.  Inst.  C.  E.,  1884-85,  LXXXI.  p.  285. 

4.  Devonshire.     The    Purification    of   Water   by   means  of   Metallic  Iron. 

Jour.  Franklin  Inst,  1890,  cxxix.  p.  449. 

STERILIZATION    BY   CHEMICALS. 

1.  Traube.      Einf aches  Verfahren  Wasser  in  grosser  Mengen  keimfrei  zu 

machen.     Zeit.  f.  Hyg.,  xvi.  p.  149. 

2.  Bassenge.     Zur   Herstellung  keimfreien   Trinkwasser    durch    Chlorkalk. 

Zeit.  f.  Hyg.,  xx.  p.  227. 

3.  Soper.     The  Purification  of  Drinking-water  by  the  Use  of  Ozone.     Eng. 

News,  1899,  XLII.  p.  250. 

4.  Soper.     The    Ozonization   of   Water.     Jour.  New   Eng.    W.    W.    Assn., 

1900,  xv.  p.  i. 

5.  Weyl.     Ueber    die  Verwendung  von  Ozone  zur   Gewinnung  keimfreien 

Trinkwassers.  Jour.  f.  Gas.  u.  Wasservers.,  1899,  XLII.  p.  809; 
also  Cent.  f.  Bakt.,  xxvi.  p.  15.  Abstract,  Eng.  News,  1900,  XLIII. 
p.  92  ;  Eng.  Record,  1900,  XLI.  p.  105. 

6.  Van't  Hoff.     Die  Reinigung  des  Trinkwassers  durch  Ozon.     Zeitschr.  /. 

Elektrochemie,  1902,  vm.  p.  504. 

7.  Erlwein.     Weitere  Beitrage  zur  Technik  der  Ozonwasserwerk.     Gesund- 

heits-Ingenieur,  1903,  xxvi.  p.  485, 

8.  The  Production  and  Uses  of  Ozone.     Engr.  1903,  xcvi.  p.  497. 

9.  Otto.     Les  Progres  Recents  Realise's  dan  PIndustrie  de  1'Ozone.     Mem. 

Soc.  Ing.  Civ.  d  France,  Nov.  1903. 

10.  Hatch.     A  Sterilized   Water-supply  at    Leavesden  Asylum.     Proc.  Inst. 

Civ.  Eng.  No.  3606. 

11.  Whipple.     Disinfection  as  a  Means  of   Water  Purification.     Proc.  Am. 

W.  W.  Assn.,  1906;  Eng.  Record,  1906,  LIV.  p.  94. 

THE  USE  OF  COPPER  SULFATE. 

1.  Moore   and    Kellerman.     Preventing    the    growth   of   Algae   in   Water- 

supplies.      Bui.  No.  64,  U.  S.  Dept.  Agr.     Eng.  News,   1904,  LI. 

p.  496- 

2.  Caird.     The    Copper    Sulfate  Treatment   for   Algae   at   Elmira,    N.    Y. 

Eng.  News,  1904,  LII.  p.  34. 

3.  Carroll.     Treatment  of  a  Reservoir  -f  the  Butte  Water  Co.  with  Copper 

Sulfate.     Eng.  News,  1904,  LII.  p.  141. 


55O  MISCELLANEOUS  PURIFICATION  PROCESSES. 

4.  Fletcher.     The  Use  of   Copper  Sulfate   to  Prevent  Algae  Growths   at 

Hanover,  N.  H.     Eng.  News,  1904,  LII.  p.  375. 

5.  Quick.     Copper    Sulfate    Treatment   of   Lakes  Clifton    and   Monticello, 

Baltimore  Water- works.     Eng.  Record,  1904,  L.  p.  374. 

6.  Prince.     The  Treatment  of  Water  with  Copper  Sulfate  at  Denver,  Colo. 

Eng.  News,  1905,  LIV.  p.  575. 

7.  Jackson.     Purification  of  Water  by  Copper  Sulfate.    Eng.  News,   1905, 

LIV.  p.  307. 

8.  A   Symposium   on   the    Relation    of    Copper    Sulfate    to    Water-supply 

Matters.     Jour.  New  Eng.  W.  W.  Assn.,  1905  ;  Eng.  News,  1905,  LIV. 
p.  306. 

9.  Brown.     Tests  of  Copper  and  Iron  Sulfates  and-  Lime  with  Mechanical 

Filters  at  Anderson,  Ind.      Proc.  Am.  W.  W.  Assn.,   1905.      Eng. 
News,  1905,  LIII.  p.  556. 

10.  Clark   and  Gage.     The   Bactericidal   Action   of   Copper.     Eng.   News, 

1906,  LV.  p.  411. 

11.  Rettger  and  Endicott.     The  Use  of  Copper  Sulfate  in  the  Purification  of 

Water.     Eng.  News,  1906,  LVI.  p.  425. 

12.  Experiments  with  Copper-Iron  Sulfate  for  Water  Purification  at  Marietta, 

Ohio.     Eng.  Record,  1906,  LIII.  p.  392. 

HOUSEHOLD    FILTERS. 

1.  Kiibler.     Unters.  ii.  d.  Brauchbarkeit   der  "  Filter  sans   pressions,   Sys- 

teme  Chamberland-Pasteur."     Zeit.  f.  Hyg.,  vin.  p.  48. 

2.  Nordtmeyer.     U.  Wasserfiltration  durch  Filter  aus  gebrannter  Infusorien- 

erde.     Zeit.  f.  Hyg.,  1891,  x.  p.  145. 

3.  Breyer.     Hyg.  Rundschau,  1891,  p.  977. 

4.  Th.  Weyl.     Berl.  klin.  Wochenschrift,  1892,  No.  23. 

5.  E.  von  Esmarch.    Uber  Wasserfiltration  durch  Steinfilter.     Cent.  f.  Bakt., 

1892,  xi.  p.  525. 

6.  Kirchner.      Unters.    ii.    d.    Brauchbarkeit    der    "  Berkefeld    Filter "    aus 

gebrannter  Infusorienerde.     Zeit.  f.  Hyg.,  1893,  xiv.  p.  299. 

7.  Gruber.     Gesichtspunkte  f.  d.   Priifung  u.  Beurtheilung  v.  Wasserfiltern. 

Cent.  f.  Bakt.,  1893,  xiv.  p.  488. 

8.  Jolin.     Einige  Untersuchungen  ii.  d.  Leistungsfahrigkeit  d.  Kieselguhr- 

Filter.     Zeit.  f.  Hyg.,  1894,  xvn.  p.  517. 

9.  Fletcher.     A  Sand  Filter  for  the  Home.     Eng.  News,  1906,  LVI.  p.  141. 

STERILIZATION    BY    HEAT. 

1.  Treatment  of  large  quantities  of  water.     Berl.  klin.  Wochensch.,   1892, 

p.  663. 

2.  Rubner   and   Davids.     Tests   of  von   Siemens'  Apparatus.     Berl.    klin. 

Wochensch.,  1893,  p.  861. 

3.  Schultz.     Expts.  with  Werner  von  Siemens'  Apparatus.     Zeit.  f.  Hyg., 

1894,  XV.  p.  206. 


C.   WORKS  FOR  THE  DISTRIBUTION  OF  WATER. 

CHAPTER    XXIV. 
PIPES   FOR   CONVEYING   WATER. 

573.  Materials  Employed. — A  variety  of  materials  may  be  employed 
for  the  construction  of  water-conduits.      If  the  conduit  is  not  under 
pressure,  the  form  of  construction  used  may  be  an  open  canal  dug  in 
the  natural  earth,   or  a  masonry  conduit  in    "cut  and  cover,"  or    a 
tunnel.      Where  the  water  flows  under  pressure  the  first  two  types  are 
not  suitable  and  a  pipe,  or  possibly  a  tunnel,  must  be  employed.     The 
method  of  construction  used  in  connection  with  canals,  masonry  con- 
duits, and  tunnels  will  be  described  in  the  next  chapter;   the  present 
chapter  will  deal  only  with  the  design  and  manufacture  of  pipes. 

The  materials  used  for  water-pipes  are  cast  iron,  wrought  iron, 
steel,  wood,  cement,  vitrified  clay,  lead,  and  occasionally  a  few  other 
materials.  The  important  requirements  for  a  water-pipe  are  strength, 
durability,  and  low  cost.  The  relative  importance  of  these  require- 
ments will  vary  under  different  circumstances,  and  this  will  lead  to  the 
use  of  different  materials  in  different  cases. 

574.  Stresses  to  be  Considered. — The  stresses  to  be  considered  in 
the  design  of  water-pipes  are  those  due  to  (i)  the  water-pressure,  (2) 
the  pressure  of  the  surrounding  earth  and  the  action  of  other  outside 
forces,  (3)  changes  of  temperature,  and  (4)  blows  and  shocks  received 
in  transportation  and  construction. 

575.  Stresses  Due  to  Water-pressure. — The  maximum  pressure  to 
be  provided  for  will  be  the  maximum  which  can  occur  under  normal 
conditions  of  operation  (usually  the  maximum  possible  static  pressure), 
plus    an    allowance    for  water-hammer.      The    former  can  readily  be 
computed,  but  the  latter  is  difficult  of  estimation. 

Sometimes  pipe-lines  are  so  designed  that  static  pressure  can  never 
occur,  the  valves  being  so  arranged  that  the  water  never  comes  to  rest. 


552  PIPES  FOR   CONVEYING    WATER. 

In  that  case  the  maximum  pressure  at  any  point  will  be  the  maximum 
pressure-head  which  can  exist  under  the  assumed  conditions  of  flow. 
This  will  be  less  than  the  static  head  by  the  amount  lost  in  friction 
from  the  open  end  of  the  pipe  to  the  point  in  question.  (See  further 
discussion  in  Art.  630.) 

The  dynamic  effect,  or  the  amount  of  water-hammer  to  be  assumed 
depends  on  many  circumstances.  It  was  shown  in  Chapter  XII  that 
it  varies  in  .general  with  the  length  of  the  pipe,  with  the  velocity  of  the 
water,  and  with  the  rapidity  with  which  the  velocity  is  changed  by  the 
action  of  valves  or  otherwise.  The  amount  to  be  allowed  should 
evidently  be  varied  according  to  the  nature  of  the  pipe-line. 

In  a  distributing  system  of  small  pipes  where  the  operation  of 
hydrants  and  large  branches  has  a  relatively  great  influence  on  the 
system,  the  allowance  should  be  large.  In  this  case  the  amount  added 
for  water-hammer  has  commonly  been  about  100  pounds  per  square 
inch,  which,  from  the  theoretical  considerations  of  Chapter  XII  would 
appear  to  be  quite  high  enough  for  all  ordinary  cases.  The  amount 
assumed  for  cast-iron  pipes  in  the  new  pipe  system  of  the  Metropolitan 
Water-  works  of  Boston  is  given  on  page  556. 

In  the  case  of  a  large  pipe-line  without  branches,  and  carefully 
protected  from  excessive  pressure  by  relief-valves  and  by  precautions 
in  operating  shut-off  valves,  the  allowance  for  water-hammer  need  be 
very  little,  especially  for  pipes  of  steel  or  wood.  It  is  true  that  any 
reduction  whatever  in  velocity,  due  to  the  closing  of  a  valve,  will  raise 
the  pressure  an  amount  proportional  to  the  length  of  the  pipe  affected, 
the  velocity  of  the  water,  and  inversely  as  to  the  time  required  in 
closing.  For  example,  if  a  stop-valve  of  a  48-inch  pipe  be  closed  in 
60  seconds,  the  average  pressure  with  four  miles  of  pipe-line  would  be 
14  pounds  per  square  inch.  Large  wooden  and  steel  pipe-lines  are 
commonly  designed  with  little  or  no  allowance  for  hammer,  but  for 
those  portions  under  light  pressure  it  would  be  well  to  make  an  allow- 
ance of  25  to  50  pounds,  depending  on  the  velocity  of  the  water  and 
the  length  of  pipe  involved.  For  those  portions  of  the  pipe  under  heavy 
pressure  the  ram  would  be  small  in  proportion  to  the  static  pressure, 
and  the  necessity  for  considering  it  would  be  less. 

The  intensity  of  the  circumferential  stress  in  a  circular  pipe  is 


(!) 


where  r  =  radius  of  pipe, 

/  =  pressure-head,  and 
t  =  thickness  of  shell. 


STRESSES  IN  PIPES.  553 

Water-pressure  must  be  specially  considered  at  sharp  curves  and 
angles.  At  such  places  the  pressure  tends  to  displace  the  pipe-line 
and  force  the  pipes  apart. 

576.  Stresses  Due  to  Earth  Filling-  and  Other  Outside  Forces.  — 
The  pressures  due  to  the  forces  here  considered  tend  to  collapse  the 
pipe.  The  effect  of  earth  filling  will  be  felt  seriously  only  for  very 
deep  trenches  and  for  large  pipes,  while  the  effect  of  traffic  is  of  impor- 
tance only  for  very  shallow  filling.  To  protect  pipes  from  injury  due 
to  traffic  a  minimum  depth  of  covering  of  2  to  3  feet  will  usually  be 
sufficient,  since  the  pipes  themselves  are  able  to  sustain  a  very  con- 
siderable load  if  it  is  distributed.  The  stresses  caused  by  heavy  loads 
of  earth  need  to  be  more  fully  considered,  and  a  rough  analysis  of  the 
problem  will  be  of  some  assistance. 

If  we  neglect  the  lateral  support  of  the  earth  and  assume  the  weight 
of  filling  applied  as  a  vertical  load,  uniformly  distributed  over  a  width 
equal  to  the  diameter  of  the  pipe,  and  ^  J£ 

assume    also    the    upward     pressure    *r  "x  '    T7~J7T 


against  the  pipe  to  be  similarly  ap-  **  " 

plied,   there  will  be   produced    equal  . 

bending  moments  at  a  and  b  (Fig.    ]\A  ^)J  [/ 

140),  but  of  opposite  sign.*     If  W—    \.  JJ  f* 

total  load  and  d  =  diameter  of  pipe,    iMf^===^jf  L 

the  bending  moment  at  these  points 

will  therefore  be 

FIG.  140. 


Assuming  h  =  depth  of  fill  in  feet;  weight  of  filling  =  100  pounds 
per  cubic  foot;  /=  safe  fibre-stress  in  bending  for  the  pipe  material; 
d  =  diameter  of  pipe  in  inches  ;  and  /  =  thickness  of  pipe  in  inches, 
we  derive,  from  the  ordinary  beam  formula,  approximately 


t  = 


(2) 


If,  for  example,  we  assume  for  cast,  iron  a  value  of/=  7000  pounds 
per  square  inch,  we  will  have  t  =  .oo6d  Vlt.  Thus  for  a  48-inch  cast- 
iron  pipe,  and  a  depth  of  filling  of  16  feet  t  =  1.15  inches,  and  for  a 

*  Because  a  similar  set  of  horizontally  applied  forces  must  reduce  the  moments 
at  a  and  b  to  zero.  See  also  a  paper  by  Wm.  H.  Searles  on  "  Deflections  and  Strains 
in  a  Flexible  Ring  under  Load."  Jour.  Assn.  Eng.  Soc.,  1895,  xv.  p.  124. 


554  PIPES  FOR   CONVEYING    WATER. 

depth  of  25  feet  t  =  1.44  inches.     The  smaller  of  these  values  is  about 
as  small  as  would  be  used  in  any  case  for  this  size  of  pipe. 

This  analysis  is  of  course  very  rough,  but  it  serves  to  give  some 
notion  of  the  maximum  stress  that  is  possible  from  earth  pressure.  It 
is  to  be  noted  that  we  have  here  entirely  neglected  the  lateral  pressures 
involved.  In  the  case  of  cast-iron  pipe  the  material  is  so  rigid  that 
the  lateral  support  received  by  the  earth  may  be  very  little  and  the 
load  will  be  supported  largely  through  the  bending  resistance  of  the 
pipe ;  but  if  the  pipe  is  relatively  flexible,  like  steel  or  even  a  wooden- 
stave  pipe,  it  will  get  much  aid  from  this  lateral  pressure,  especially  if 
the  earth  is  well  tamped  in  place.  Cases  of  the  breakage  of  cast-iron 
pipe  under  high  embankments  have  occurred,  but  the  above  analysis 
indicates  that  usually  no  account  need  be  taken  of  earth  pressures  when 
the  depth  of  filling  is  less  than  10  or  15  feet. 

In  the  case  of  large  steel  pipes  built  of  comparatively  thin  material 
stiffening-rings  are  sometimes  used  to  support  heavy  loads,  as,  for 
example,  on  the  large  Brooklyn  line,  where  stiffening-rings  of  4  X  4  X 
f-inch  angles  were  used  under  all  waterways  and  wherever  the  covering 
exceeded  6  feet.  A  covering  of  concrete  is  also  sometimes  employed 
to  give  additional  strength.  In  most  cases,  however,  no  trouble  will 
be  had  if  the  back-filling  is  well  tamped,  and  the  pipe  perhaps  tem- 
porarily supported  by  interior  braces.  Where  the  filling  is  not  well 
done  steel  pipes  have  been  greatly  flattened  at  the  top  by  the  load  of 
earth.  At  Portland,  Oregon,  a  flattening  of  4  inches  was  caused  in  this 
way.  Experiments  there  made  showed,  however,  that  a  distortion  of 
as  much  as  8f  inches  in  a  42 -inch  steel  pipe  caused  no  leaks,  although 
a  flattening  of  only  if  inches  caused  a  permanent  set  of  J  inch.* 

Experiments  on  a  6 1 -inch  cast-iron  pipe,  ij  inches  thick,  for  the 
Sudbury  conduit,  showed  a  difference  of  from  .005  to  .01  foot  between 
horizontal  and  vertical  diameters  due  to  deflection  from  its  own  weight, 
and  a  maximum  deflection  of  .015  foot  under  a  load  of  4  feet  of 
gravel,  t 

Another  possible  outside  force  which  should  be  considered  in  the 
design  is  the  unbalanced  pressure  due  to  the  creation  of  a  partial 
vacuum  when  emptying  the  pipe.  The  capacity  of  the  air-valves 
should  be  made  such  as  to  preclude  dangerous  pressures  from  this 
source. 

577.  Stresses  Due  to   Temperature  Changes. — If  no  expansion  or 


*  Trans.  Am.  Soc.  C.  E.,  1897,  xxxvin.  p.  93. 
f  Eng.  Record,  1898,  XXXVIII.  p.  51. 


CAST-IRON  PIPE.  555 

contraction  is  allowed  in  a  pipe-line,  the  longitudinal  stresses  due  to 
changes  of  temperature  will  be  equal  to 

s  =  ETc, (3) 

where  s  =  intensity  of  stress ; 

E  —  modulus  of  elasticity ; 
T  =  change  of  temperature ; 
c  —  coefficient  of  expansion. 

Temperature  stresses,  as  a  rule,  need  not  be  considered  except  in 
the  case  of  riveted  steel  pipe.  (See  Art.  593.) 

578.  Stresses  Caused  in  Transportation  and  Construction. — Such 
materials  as  cast-iron  and  vitrified  pipe  require  a  considerable  thick- 
ness to  provide  for  these  stresses.  The  necessary  allowance  for  this 
purpose  has  been  determined  by  practical  experience,  and  account  of 
it  is  taken  in  the  formulas  and  rules  for  thickness. 


CAST-IRON   PIPE. 

579.  General. — Cast  iron  is  the  most  widely  used  material  for  water- 
pipe.      By  reason  of  its  moderate  cost,  its  durability,  and  the  conve- 
nience  with  which   it  may  be  cast  in  any  desired  form  it  is  almost 
universally  employed  for  the  pipes  and  various  special  forms  of  distrib- 
uting systems.      It  is  also  frequently  employed  for  large  pipe-lines, 
and  is  now  easily  obtained  in  any  desired  diameter  up  to  6  feet  or 
more.      Cast-iron  pipes  are  made  in  lengths  of  about  12  feet,  which  are 
joined   together  usually  by  the   bell-and-spigot  joint  run  with   lead. 
Branches  and  other  irregular  forms  are  used  for  connections.      These 
are  called  special  castings,  or  simply  ' 'specials." 

580.  Thickness  and  Weight  of  Cast-iron  Pipe. — The  material  used 
for  pipes  is  usually  required  to  have  a  tensile  strength  of  from  16,000 
to    18,000   pounds   per  square   inch.      A  factor  of  safety  of  5  maybe 
assumed   where    proper    allowance    is    made   for    water-hammer.      In 
addition  to  the  thickness  required  to  sustain   water- pressure  a  small 
addition  must  be  made  to  allow  for  eccentricity  of  casting  and  to  pro- 
vide sufficient  strength  to  bear  transportation.      One-tenth   of  an  inch 
should  be  sufficient  for  the  first  allowance.      For  the  second  object  it 
would  seem  that  no  allowance  at  all  need  be  made  for  such  sizes  and 
pressures   that   the  thickness   required    to  sustain   the   water-pressure 
would  be  large.      However,  it  is  customary  to   make   some  allowance 


PIPES  FOR    CONVEYING    WATER. 

for  all  sizes.      The  total  amount  allowed  for  both  the  above-mentioned 
objects  varies  in  the  different  formulas  from  about  .25  to  .35  inch. 

Different  formulas  are  used  by  different  pipe-foundries  and  by  dif- 
ferent cities  in  determining  the  thickness  of  pipe.  A  formula  which 
commends  itself  as  being  simple  in  form  and  rational  in  its  make-up 
is  that  used  by  the  Metropolitan  Water-  works  of  Boston.  It  is 


3300 

where  t  —  thickness  in  inches  ; 

/  =  static  pressure  in  pounds  per  square  inch; 
p'  =  allowance  for  water-hammer  in  pounds  per  square  inch  ; 
r  =  radius  of  pipe  in  inches  ; 
0.25  =  allowance  for  eccentricity,  deterioration,  and  safety  in  hand- 

ling. 
The  value  of/'  is  to  be  taken  as  follows: 

Size  of  Pipe.  Value  of/'. 

3-in.  to  10-in  ............  120 

12-in  ...............  no 

i6-in  ...............  100 

2O-in  .............  90 

24-in  ...............  85 

30-in  ...............  80 

36-in  ........  .  ......  75 

42-in.  to  6o-in  ...........  70 

This  formula  assumes  a  strength  of  16,500  pounds  per  square  inch 
and  a  factor  of  safety  of  5.  It  gives  pipe  somewhat  thinner  than  that 
formerly  used  by  the  Boston  Water-  works,  and  about  as  light  as  it  is 
advisable  to  use.  It  properly  varies  the  allowance  for  water-hammer 
according  to  the  size  of  pipe. 

Large  cities  usually  adopt  a  few  standard  thicknesses  for  each  size, 
corresponding  to  certain  pressures,  the  pipes  designed  for  the  different 
pressures  being  designated  as  Class  A,  Class  B,  etc.  The  variations 
between  classes  usually  correspond  to  a  difference  of  pressure  of  about 
50  pounds  per  square  inch.  The  various  pipe-foundries  have  likewise 
their  standard  weights  for  different  sizes,  which  differ  more  or  less 
among  themselves  and  also  differ  from  the  various  city  standards.  For 
large  orders  of  pipe  it  is  easy  to  secure  any  designated  weights,  but  for 
small  orders  it  will  be  economy  to  select  from  the  standards  given  in 
the  manufacturers'  lists  that  weight  which  will  come  nearest  to  the 
weight  desired. 


PIPE  JOINTS.  557 

Standard  specifications  for  water  pipe  have  been  adopted  by  the 
New  England  Water- Works  Association,  which  include  standards  as  to 
weights  and  dimensions  of  various  classes  of  pipe  and  of  various  specials. 
These  are  to  be  commended  as  being  the  result  of  much  careful  study 
and  discussion  and  as  aiding  greatly  in  standardizing  and  improving 
current  practice  in  this  important  particular.*  Table  No.  74  furnishes 
data  in  accordance  with  these  standards. 

In  determining  the  thickness  of  various  classes  of  pipe  formula  (4) 
has  been  used  and  pressures  from  50  to  500  feet  assumed,  although  it  is 
not  the  intent  of  the  specifications  to  recommend  any  particular  class 
for  a  given  pressure.  Variations  in  outside  diameter  are  made  as  few 
as  practicable,  the  variation  in  thickness  being  secured  principally  by 
varying  the  inside  diameter.  The  variations  in  special  castings  are 
fewer  than  in  straight  pipe. 

58 1.  Joints.  —  The  Ordinary  Bell-and-spigot  Joint.  —  The  joint  which 
is  ordinarily  employed  in  this  country  is  the  bell-and-spigot  joint.  The 
space  between  bell  and  spigot  is  filled  with  lead,  which  is  calked  solidly 
into  place  so  as  to  be  water-tight.  Many  forms  of  bell  or  socket  have 
been  devised,  but  practice  has  come  to  be  quite  uniform  on  this  point, 
and  is  well  represented  by  the  standard  shown  in  Fig.  142.  The  chief 
requisites  of  a  bell  and  spigot  are:  1st,  sufficient  space  to  allow  of 
thorough  calking,  but  no  more  space  than  necessary  ;  2d,  sufficient 
depth  of  bell  to  enable  a  tight  joint  to  be  made  and  to  give  considerable 
lateral  strength  to  the  pipe ;  3d,  sufficient  strength  of  bell  to  resist  the 
bursting-force  due  to  calking.  It  will  be  noted  from  the  illustrations 
that  a  groove  is  formed  on  the  interior  of  the  bell.  This  is  for  the  pur- 
pose of  holding  the  lead  more  firmly  in  place.  The  interior  surface  of 
the  pipe  at  the  joints  should  be  as  smooth  as  possible.  In  the  case  of 
some  large  pipe  recently  laid,  the  joints  on  the  interior  of  the  pipe 
were  filled  with  Portland-cement  mortar  in  order  to  give  a  smooth 
surface. 

In  Table  No.  75  are  given  the  various  dimensions  of  standard  bell 
and  spigot  in  accordance  with  the  specifications  of  the  New  England 
Water- Works  Association  (Fig.  142),  together  with  amounts  of  lead 
and  packing  required  per  joint. 

The  ordinary  bell-and-spigot  joint  with  lead  packing  will  enable  pipes 
to  expand  and  contract  under  moderate  changes  of  temperature  such  as 
occur  with  buried  pipes. 

*  These  specifications  may  be  had  from  the  Secretary  of  the  New  England  Water- 
Works  Association,  Boston,  Mass.  They  contain  full  tables  of  pipe  and  special 
castings.  See  also  Jour.  New  Eng.  W.  W.  Ass'n,  December,  1902,  March,  1903. 


558 


PIPES  FOR    CONVEYING    WATER. 


111 

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PIPE  JOINTS. 


559 


Curves  of  large  radius  can  be  constructed  with  straight  pipe  by 
deflecting  each  length  slightly.  In  this  way  it  is  possible,  with  a 
reasonable  deflection,  to  lay  4-  to  8-inch  pipe  to  a  curve  of  I5o-foot 
radius,  a  1 6-inch  pipe  to  a  25<D-foot  radius  and  a  36-inch  pipe  to  a 
5OO-foot  radius. 

t-a 


FIG.  142.  —  STANDARD  BELL  AND  SPIGOT,  NEW  ENG.  W.  W.  ASS'N  STANDARD. 

TABLE    NO.    75. 

GENERAL    DIMENSIONS    OF   STANDARD    BELL-AND-SPIGOT   PIPE   ACCORDING   TO   THE 
SPECIFICATIONS    OF   THE    NEW    ENGLAND    WATER-WORKS    ASSOCIATION. 


Nominal 
Diameter, 
Inches. 

Classes. 

Dimensions  in  Inches. 

Average  Weight  of  Lead 
per  Joint. 

Weight  of 
Jute  Gasket 
per  Joint. 

"  a  " 

"j" 

«  c  » 

"/" 

With 
Gasket. 

Solid 
Lead. 

4 

All 

•5° 

•30 

3.00 

0.40 

7.OO 

9.25 

.  IO 

6 

M 

•5° 

.40 

3.00 

0.40 

9-75 

12.75 

•15 

8 

(1 

•5° 

•5° 

3-50 

0.40 

12.50 

18.75 

•25 

IO 

M 

•5° 

•5° 

3  5<> 

0.40 

I5.25 

23-25 

•3° 

12 

« 

•50 

.60 

3-5° 

0.40 

18.00 

27.00 

•35 

14 

M 

•50 

.70 

3-5o 

0.40 

20.50 

31.00 

.40 

16 

«< 

•75 

.80 

4.00 

o.  50 

3L25 

50-50 

•65 

18 

M 

•75 

.90 

4.00 

o.  50 

34-75 

55-50 

.70 

20 

« 

•75 

2.00 

4.00 

0.50 

38.50 

62.00 

.80 

24 

«( 

2.OO 

2.10 

4.00 

0.50 

45-50 

74.00 

•95 

30 

II 

2.00 

2.30 

4-5° 

0.50 

56.00 

100.50 

i-55 

36 

42 

« 
(i 

2.OO 
2.00 

2^80 

4-5° 
5.00 

o.  50 
0.50 

67.00 

77-5° 

120.50 
154.00 

2.60 

48 

M 

2.OO 

3.00 

5.00 

o.  50 

88.50 

176.00 

3.00 

54 

A,  B,  C,  D 

2.75 

3.20 

5-5o 

0.50 

99-50 

215.00 

3-95 

54 

E,  F 

2-75 

3.80 

5-5° 

0.50 

IOO.OO 

215.5° 

3-95 

60 

A,  B,  C,  D 

2.75 

3-40 

5-5° 

o.  50 

no.  50 

239  .  oo 

4.40 

60 

E,  F 

2.75 

4.00 

5-5° 

o.  50 

I  I  I  .  OO 

24  i  .  oo 

4.40 

582.  Other  Forms  of  Joints.  —  In  England  and  at 
this  country  the  bored  and  turned  joint  has  been 
used.  A  form  of  this  type  of  joint  is  shown  in 
Fig.  1 43.  The  inside  of  the  socket  and  outside  of 
the  spigot  are  turned  to  an  accurate  fit,  and  the 
joint  is  made  by  simply  driving  the  pipes  together 
by  means  of  a  wooden  ram.  Sometimes  cement 
filling  is  used  in  addition.  In  some  cases  the 
cost  of  boring  and  turning  is  reported  to  be  less 
than  that  of  lead  joints,  while  in  other  cases  the 


a  few  points  in 


FIG.  143. 
TURNED  JOINT. 

opposite  is  true. 


560  PIPES  FOR   CONVEYING    WATER. 

Wooden  wedges  have  been  employed  to  a  limited  extent  in  place 
of  lead  packing.  At  Yarmouth,  Nova  Scotia,  such  joints  have  been  in 
use  since  185 1 ,  and  have  proven  so  durable  that  they  have  recently  been 
adopted  as  the  standard  for  that  place.  The  wedges  are  made  from 
clear,  dry,  pine  staves.  The  cost  is  stated  to  be  from  6  to  13  cents 
per  joint  for  sizes  from  8  to  24  inches  in  diameter.  Joints  of  this  sort 
have  been  found  in  perfect  condition  after  a  lapse  of  from  forty  to  forty- 
five  years.*  This  form  of  joint  would  probably  be  advantageous  where 
electrolysis  is  to  be  feared. 

A  joint  that  has  been  used  somewhat  in  Europe,  and  which  is  espe- 
cially suitable  for  temporary  work,  is  made  by  means  of  a  solid  rubber 
ring.  The  ring  is  inserted  in  the  socket  near  the  outside  edge  and  is 
rolled  back  by  pushing  the  pipe  into  place.  For  this  joint  a  smooth 
bell  would  be  preferable.  Other  forms  of  rubber  joints  have  been 
employed  occasionally,  sometimes  for  expansion  purposes.  (Art.  641.) 

For  inside  work  and  connections  in  confined  locations  the  flanged 
joint  is  more  convenient  than  the  bell  and  spigot.  It  is  also  better 
suited  for  temporary  work.  The  flanges  are  faced  carefully  at  right 
angles  to  the  axis  of  the  pipe,  and  the  joint  is  bolted  together  with  rub- 
ber or  other  packing  between  the  flanges.  Various  standards  are  used 
for  proportioning  the  flanges,  as  to  thickness,  number  of  bolts,  etc., 
for  which  reference  may  be  made  to  the  various  trade  circulars,  t 

For  joining  pieces  of  pipe  a  sleeve  is  used,  which  is  essentially  a 
short  piece  of  pipe  with  two  bells.  It  is  illustrated  in  Fig.  144. 
When  a  pipe  is  cut  to  make  a  connection  it  is  usual  to  shrink  a  small 
half-oval  or  semicircular  band  on  the  end  to  take  the  place  of  the  rib 
which  forms  the  ordinary  spigot. 

583.  Special  Castings. — The  ordinary  special  castings  required  are 
the  J,  -J,  and  Ty  bends  or  curves,  T's  and  crosses,  or  three-way  and 
four-way  branches,  Y  branches,  blow-off  branches,  offsets,  sleeves, 
caps,  and  plugs.  The  various  forms  are  illustrated  in  Fig.  144.  Many 
of  the  larger  cities  have  their  own  standard  designs  for  specials  as  well 
as  for  straight  pipe,  which  differ  more  or  less  from  the  manufacturers' 
standards.  For  the  smaller  cities  it  will  be  much  the  more  econom- 
ical to  use  either  the  manufacturers'  standards  or  those  of  some  neigh- 
boring large  city.J 

The  various  branches  are  manufactured  either  with  part  bell  and 
part  spigot  ends,  or  with  all  bell  ends.  The  latter  form  is  usually 

*  Jour.  N.  E.  Water-works  Assn.,  1900,  xv.  p.  34. 

t  See  also  standard  proposed  by  tne  Am.  Soc.  M.  E.  in  Trans.  Am.  Soc.  M.  E.. 
1893,  xiv.  p.  48.  t  See  standards  of  the  New  England  W.  W.  Assn. 


CAST-IRON  PIPE. 


56l 


preferred  for  branches,  as  it  enables  connections  to  be  readily  made  by 
means  of  pieces  of  pipe. 

In  designing  special  castings  consideration  should  be  given  to  the 
fact  that  such  castings  cost,  as  a  rule,  about  twice  as  much  per  pound' 
as  straight  pipe.  They  should  therefore  be  as  light  and  compact  as 


Bend. 


Reducer. 


Offset. 


Cap. 


Y  Branch. 


Four-way  Branch, 


Blow-off  Branch. 
FIG.  144. — SPECIAL  CASTINGS. 


Sleeve. 


practicable.  They  are  made  of  the  same  thickness  as  the  corresponding 
straight  pipe,  but  with  a  less  number  of  variations  for  the  different  pres- 
sures. The  general  form  of  specials  should  be  such  as  to  cause  as 
little  disturbance  in  the  water  in  passing  around  angles,  etc.,  as  prac- 
ticable. This  is  of  considerable  importance  where  the  velocity  is  high, 
and  hence  should  be  carefully  considered  in  the  design  of  hydrants  and 
hydrant  branches. 


562 


PIPES  FOR    CONVEYING    WATER. 


584.  Material  and  Method  of  Manufacture.  —  Quality  of  Iron.  — 
Water-pipe  should  be  made  of  the  best  quality  of  gray  iron,  uniform  in 
grain  and  soft  enough  to  be  readily  worked.  The  metal  should  be 
made  without  the  admixture  of  cinder-iron  or  other  inferior  metal,  and 
no  ordinary  scrap  should  be  used  in  the  manufacture.  A  mixture  of 
pig  irons  is  usually  required  to  give  the  best  results,  the  proper  propor- 
tions being  a  matter  of  experience.  An  ordinary  specification  for  the 

strength  of  -the  material  is  that  a 
test-bar  2  inches  by  I  inch  in  cross- 
section,  placed  on  supports  24 
inches  apart,  shall  sustain  a  load 
of  1900  pounds  at  the  center,  and 
shall  have  a  deflection  of  at  least 
T3T  inch  before  fracture.  This  re- 
quirement insures  a  certain  amount 
of  toughness,  or  resilience,  as  well 
as  strength.  Frequently  a  tension- 
test  is  required,  the  ultimate 
strength  specified  being  from  16,- 
ooo  to  18,000  pounds  per  square 
inch.  It  should  be  specified  that 
test-bars  shall  be  poured  at  any 
time  during  the  day  that  the  in- 
spector desires. 

585.  Molding  and  Casting.  — 
Water-pipes  are  now  always  cast 
in  vertical  molds,  and  should  be 
required  to  be  cast  with  the  bell 
end  down,  except,  perhaps,  for  the 
smaller  sizes.  The  form  of  mold 
Lused  is  shown  in  Fig.  145.  The 


A,  Flask. 
C,  Spindle. 
£,  Roping. 


B,  Base. 
D,  Socket. 
F,  Bead  ring. 


/,  Sand. 
FIG.  145. — PIPE-MOLD. 

(From  Cassier^s  Magazine,  vol.  vm.) 


cores  are  made  by  winding  the 
socket-ring  D  and  the  spindle  C 
with  hay  rope,  then  coating  with 
damp  sand  and  shaping  in  a 
lathe.  Much  care  is  required  in 
molding  and  casting  to  secure  good  results,  and  in  spite  of  the  greatest 
care  much  pipe  will  need  to  be  rejected  if  the  inspection  is  properly 
done.  In  the  case  of  a  contract  of  any  considerable  size  the  city  should 
always  employ  a  competent  inspector  to  protect  its  interests. 

Cores  should  be  accurately  centered  so  that  the  shell  will  be  of 


CAST-IRON  PIPE.  563 

uniform  thickness,  and  the  bells  and  spigots  should  be  truly  circular. 
The  pipe  should  be  free  from  all  surface  imperfections  that  will  weaken 
it  or  lessen  its  durability,  such  as  checks,  blow-holes,  sand-holes,  and 
cold-shuts ;  and  should  be  smooth  and  free  from  lumps,  scales,  blis- 
ters, etc.  No  plugging  of  blow-holes  or  the  like  should  be  permitted. 
Care  should  be  taken  to  have  the  core  as  smooth  as  possible,  and  firm 
enough  to  support  the  metal.  It  frequently  happens  that  ridges  are 
formed  on  the  interior  of  the  pipe,  due  to  the  compression  of  weak 
cores.  The  smoothness  of  the  interior  is  specially  important  in  order 
that  the  resistance  to  the  flow  of  water  may  be  a  minimum.  Specials 
should  be  true  to  the  designated  form. 

After  casting,  the  pipe  should  be  allowed  to  cool  before  being 
taken  from  the  molds,  in  order  to  prevent  unequal  contraction.  As 
soon  as  the  pipe  is  uncovered  it  should  be  thoroughly  cleaned  of  sand 
by  means  of  wire  and  other  brushes,  and  should  then  be  inspected  for 
surface  imperfections  and  for  thickness  and  form.  To  detect  surface 
defects  the  inspector  uses  a  light,  pointed  hammer,  and  for  measuring 
the  thickness  calipers  are  applied  to  the  pipe  at  several  points,  an 
allowance  of  from  ^  to  -^  inch  being  made  for  variations  from  the 
exact  specified  dimensions.  The  forms  of  the  sockets  and  spigots  are 
tested  by  templates.  Defective  spigots  are  often  cut  off  in  a  lathe  and 
a  new  spigot  made  as  described  on  page-  560.  A  small  percentage 
of  such  defective  pipe  is  usually  allowed  by  the  specifications.  Each 
piece  of  pipe  should  have  cast  upon  it  a  serial  number  to  designate 
the  number  of  the  cast  and  the  year,  and  also  letters  to  designate  the 
manufacturer. 

586.  Coating. — To  prevent  rapid  deterioration,  all  pipe  should 
receive  some  sort  of  protective  coating.  The  first  successful  process 
for  coating  was  invented  by  Dr.  Angus  Smith  in  1849,  and  was  intro- 
duced into  the  United  States  in  1858  by  Mr.  Kirkwood.  This  coating 
was  composed  of  a  varnish  of  coal-tar  and  linseed-oil.  The  ordinary 
coating  as  now  used  is  commonly  called  the  Angus  Smith  coating,  but 
it  differs  considerably  from  that  originally  employed.  As  now  applied 
in  practice  it  usually  consists  of  ordinary  coal-tar,  or  distilled  tar  with 
dead-oil  added  to  give  fluidity  to  the  material.  Sometimes  resin  or 
creosote  is  added.  In  the  process  of  coating,  the  tar  is  maintained  at 
a  temperature  of  about  300  degrees  Fahrenheit.  The  pipe  is  also 
usually  heated  to  about  the  same  temperature  before  dipping,  but  is 
sometimes  dipped  cold  and  allowed  to  remain  in  the  bath  until  it 
acquires  the  same  temperature  as  the  tar.  Some  specifications  require 
the  pipe  to  be  removed  and  then  redipped  in  order  to  give  a  thicker 


5<54  PIPES  FOR   CONVEYING    WATER. 

coating.  When  cool  the  coating  should  be  hard,  tough,  and  smooth, 
and  should  not  loosen  under  the  blows  of  a  hammer. 

To  obtain  good  results  the  pipe  must  be  absolutely  clean  and  free 
from  rust  before  dipping;  otherwise  the  tar  will  not  adhere  to  the  iron. 
It  is  supposed  that  most  of  the  corrosion  which  appears  in  the  interior 
of  the  pipe  starts  at  a  point  where  there  is  some  minute  defect  in  the 
coating,  and  it  is  therefore  very  important  that  the  coating  be  con- 
tinuous. In  some  recent  work  done  in  Boston  the  interior  of  the  pipe 
has  received  an  additional  coating  of  paraffine  or  vulcanite  applied 
with  a  brush,  in  the  hope  that  any  minute  holes  in  the  coating  would 
be  filled.  Any  injury  which  occurs  in  handling  should  be  remedied  by 
the  application  of  some  kind  of  asphalt  paint  or  tar  varnish. 

Asphalt  has  been  tried  in  various  ways  as  a  coating  for  cast-iron 
pipe,  but  without  much  success.  It  does  not  appear  to  adhere  as  firmly 
as  tar. 

587.  Testing  and  Weighing. — After  coating,  each  section  of  pipe 
should  be  subjected  to  an  hydraulic  test  of  from  200  to  300  or  more 
pounds  per  square  inch,  according  to  the  pressure  for  which  the  pipe 
is  designed,   the  test  pressure    being  considerably  above  the  actual 
working  pressure.      While   undergoing  this  test  the   pipe   should   be 
sharply   rapped  from  end  to  end  with   a  hand-hammer  to  detect  any 
weakness.      After  this  test  each  piece  of  pipe  should  be  weighed  and 
the  weight  plainly  marked  thereon  in  paint.      Inasmuch  as  the  pipe 
cannot  be  cast  to  exact  weight,  a  maximum  allowable  variation  of  3  to 
4  per  cent,  from  that  specified  is  usually  permitted.      Lighter  weights 
will  cause  the  pipe  to  be  rejected ;  heavier  weights  will  be  allowed, 
but  not  paid  for. 

588.  Durability  of  Cast-iron  Pipe. — The  life  of  well-coated  cast-iron 
pipe  is  still  to  be  determined.      The  question  of  corrosion  is  an  impor- 
tant one,  not  only  with  respect  to  the  life  of  the  pipe,  but  on  account 
of  the  fact  that  corrosion  will  greatly  reduce  its   carrying  capacity. 
Considerable  corrosion  may  indeed  take  place  on  the  interior  of  the 
pipe  without  greatly  impairing  its  strength. 

The  rapidity  of  the  corrosion  depends  largely  upon  the  character  of 
the  water,  and,  generally  speaking,  those  waters  containing  considera- 
ble amounts  of  free  carbonic  acid  are  the  worst  in  this  particular. 
Many  instances  are  reported  where  well-coated  pipes  appear  to  be 
practically  unchanged  after  forty  or  fifty  years  of  use.  In  other  cases, 
especially  where  the  water-supply  is  soft,  some  corrosion  will  take 
place  in  a  few  years.  At  still  other  places  the  coating  appears  to 
have  been  worn  away  or  to  have  disintegrated.  Usually  some  corro- 


WROUGHT-IRON  AND    STEEL   PIPE.  565 

sion  will  take  place  in  ten  or  fifteen  years  even  with  well-coated  pipes. 
In  most  cases  the  corrosion  is  much  less  rapid  after  it  has  proceeded 
to  a  certain  extent,  and  it  is  probably  safe  to  say  that  well-coated  pipe 
will  last  at  least  fifty  years,  and  probably  much  longer. 

The  internal  corrosion  of  pipes  occurs  in  a  different  way  from  the 
ordinary  rusting  of  iron.  Bunches  or  knobs,  called  tubercles,  form  on 
the  surface,  which  consist  for  the  most  part  of  oxid  of  iron,  with  some 
silica,  lime,  and  organic  matter.  These  may  increase  to  a  size  of  i^ 
to  2  inches  in  diameter,  and  \  to  I  inch  thick.  At  the  base  of  each 
tubercle  is  usually  found  a  spot  where  the  iron  is  badly  corroded  and 
often  so  soft  that  it  can  be  cut  with  a  knife.  This  soft  spot  may  be 
very  small,  while  the  coating  around  may  be  well  preserved.  The 
tubercle  is  supposed  to  start  at  a  point  where  the  original  coating  is 
defective,  a  very  small  defect  being  sufficient  to  allow  this  to  occur. 
The  theory  of  the  corrosion  is  that  the  iron  is  attacked  by  the  carbonic 
acid  in  the  water,  thus  forming  ferrous  carbonate,  which  is  then  oxid- 
ized to  ferric  hydrate  by  the  oxygen  dissolved  in  the  water.  The 
carbonic  acid  is  thus  set  free  and  is  capable  of  further  attacks  upon 
the  metal.  A  depression  is  gradually  formed  in  which  the  tubercle  is 
built  up. 

The  corrosion  of  the  exterior  of  a  pipe  depends  largely  upon  the 
character  of  the  soil.  Ashes,  cinders,  and  the  like  are  to  be  avoided 
for  filling. 

WROUGHT-IRON   AND    STEEL    PIPE. 

589.  Advantages  of  Wrought-iron  and  Steel  Pipe. — Wrought  iron 
and  steel  have  been  used  to  a  considerable  extent  for  water-pipes,  and 
for  large  pipe-lines  these  materials  present  considerable  advantage 
over  cast  iron.  The  question  is  purely  an  economical  one,  and  in  its 
consideration  several  factors  enter.  Since  steel  is  much  stronger  than 
cast  iron,  the  use  of  it  will  give  a  much  lighter  pipe,  an  advantage 
as  regards  transportation,  but  a  disadvantage  as  regards  durability, 
especially  for  small  sizes.  Special  forms  are  not  so  readily  constructed 
of  steel,  so  that  for  distributing-mains  cast  iron  is  much  preferable. 
Another  disadvantage  of  steel  pipe  is  that  with  the  ordinary  riveted 
joints  a  considerably  larger  pipe  is  required  than  if  a  smooth  cast-iron 
pipe  is  used.  Thus  for  a  diameter  of  42  inches  the  value  of  c  for  a  riv- 
eted steel  pipe  may  be  taken  at  no  (page  246),  while  for  a  new  cast- 
iron  pipe  it  is  about  130.  The  capacity  of  the  steel  pipe  is  therefore 
only  85  per  cent  of  that  of  a  cast-iron  pipe  of  the  same  diameter.  The 


566  PIPES  FOR    CONVEYING    WATER. 

discharge  being  nearly  proportional  to  d*,  the  necessary  size  of  steel 
pipe  to  equal  the  cast-iron  pipe  in  capacity  would  be  given  by  the  pro- 

portion -=-  =  (  —  ),  whence  x  —  44  £  inches,  which  is  about  6  per  cent 
.  o  5         4-2 

larger  than  the  cast-iron  pipe. 

Steel  pipe  is  specially  adapted  to  long  pipe-lines  with  few  of  no 
branches,  also  for  high  pressures,  and  for  resisting  other  unusual 
stresses.  Several  large  pipe-lines  have  been  built  of  steel  within  the 
last  few  years,  and  it  may  be  predicted  that  the  use  of  this  material 
will  be  greatly  extended  in  the  future  as  better  means  for  its  protection 
are  devised.  Even  allowing  for  its  more  rapid  corrosion,  it  will  prove 
cheaper  in  many  cases  to  renew  it  than  to  invest  the  additional  money 
required  for  the  cast-iron  pipe.  On  the  other  hand,  the  inconvenience 
of  renewal  may  be  largely  against  the  use  of  steel. 

Wrought  iron  has  been  entirely  superseded  by  steel  for  riveted 
pipes.  Some  experiments  indicate  less  corrosion  in  the  case  of 
wrought  iron,  but  the  difference  is  not  great  enough  to  be  worth  much 
consideration. 

590.  Quality  of  the  Material.  —  The  material  used  for  steel   pipes 
should  be  soft  open-hearth  steel  of  a  tensile  strength  of  about  60,000 
pounds  per  square  inch,    elastic   limit  one-half  of  ultimate  strength, 
elongation  22  to  25  per  cent,  and  reduction  of  area  50  per  cent.      This 
material  is  about  the  same  as  now  used  in  the  best  stand-pipe  construc- 
tion.     A   good   quality  of  material  is  required  to   resist  the  shocks  to 
which  pipe-lines  are  often  subjected,  and  to  withstand  safely  the  work 
of  forging,  punching,  and  calking. 

591.  Thickness  of  Shell  —  If  s  =  allowable  stress  per  square  inch  on 
gross  section,  the  required  thickness  is  given  by  the  equation 


where  •/  =  total   pressure   per  square  inch,   including  allowance  for 

water-hammer,  and 
r  =  radius  of  pipe  in  inches. 

The  value  of  s  depends  upon  the  method  of  construction.  If  the 
pipe  is  a  riveted  pipe,  the  longitudinal  joints  are  usually  double-riveted, 
and  as  such  have  an  efficiency  of  from  60  to  70  per  cent.  If  water- 
hammer  is  properly  taken  into  account,  the  safe  stress  on  net  area  may 
be  taken  at  about  15,000  pounds  per  square  inch,  whence  the  stress  on 
gross  area  will  be  about  10,000  pounds  per  square  inch,  which  would 


WROUGHT-IRON  AND    STEEL   PIPE.  5O/ 

be  the  value  of  s  to  be  used  in  the  preceding  equation.  For  very  large 
pipes  triple-riveted  joints  may  be  employed,  in  which  case  the  efficiency 
will  be  about  75  per  cent  (see  also  Art.  593). 

In  order  to  equalize  somewhat  the  life  of  pipes  of  various  sizes,  and 
at  the  same  time  to  prolong  it,  an  allowance  of  a  small  amount,  such 
as  y1^  inch,  may  well  be  added  to  the  thickness  determined  from  the 
formula. 

592.  Joints. — Small  sizes  of  pipe  may  be  made  by  means  of  the  lap- 
welded  joint,  or  the  spirally- riveted  joint,  or  the  longitudinal  lap-riveted 
joint.      Such  pipes  are  made  in  sections  of  1 2  or  15  feet  which  are  con- 
nected in  the  field  in  various  ways,  such  as  by  a  screw-coupling,  or  by 
means  of  a  cast-iron  bell  and  a  spigot  consisting  of  a  steel  or  wrought- 
iron  band,  or  by  riveting,  or  by  merely  driving  the  sections  together. 
For  large  sizes  riveted  longitudinal  and  circular  joints  are  usually  em- 
ployed.     Single  sheets  are  bent  and  riveted  to  form  one  section  of  pipe, 
which  may  be  made  either  cylindrical  in  form,  or  made  with  a  slight 
taper  and  the  sections  put  together  stove-pipe  fashion.    Lap-joints  have 
been  commonly  used,  but  this  form  of  joint  offers  considerable  obstruc- 
tion to  the  flow  of  water,  so  that  in  some  of  the  later  pipes  butt-joints 
have  been  adopted,  and  it  has  been  proposed  also  to  employ  counter- 
sunk rivets.      The  value  of  butt-joints  and  countersunk  rivets  would  be 
proportionally  greater  the  thicker  the  plates.      Whether  they  would  be 
economical  would  depend  on  the  extra  cost  involved  as  compared  with 
the  saving  effected  by  the  reduction  in  diameter  rendered  possible. 

In  the  construction  of  steel  pipes  several  sections  are  riveted  to- 
gether at  the  shop,  usually  enough  to  make  a  length  of  20  to  30  feet. 
These  sections  are  then  transported  to  the  field  and  riveted  together 
in  place.  Special  forms  of  joints,  such  as  described  for  small  pipes,  are 
also  sometimes  used  for  large  pipes,  but  probably  the  safest  joint  for 
the  circular  seams  is  the  well-calked  riveted  joint. 

Riveted  joints,  both  in  the  shop  and  in  the  field,  should  be  thor- 
oughly calked  and  tested  by  water-pressure. 

593.  Design  of  the  Riveting. — The  design  of  the  riveting  follows 
the  same  general  principles  as  employed  elsewhere,  and  as  more  fully 
discussed  in  the  chapter  on  stand-pipe  design,  Art.  720.      The  size  of 
rivets  is  usually  made  about  twice  the  plate  thickness  up  to  a  maximum 
diameter  of  about  \\  inches.     The  circular  joints  can  usually  be  made 
strong  enough  by  single  riveting,  but  economy  requires  the  longitudi- 
nal joints  to  be  double-  or  triple-riveted.      For  any  given  size  of  rivet 
the  spacing  is  determined  by  making  the  shearing  strength  of  the  rivet 
equal  to  the  tensile  strength  on  net  section ;  and  this  strength  divided 


568  PIPES  FOR    CONVEYING    WATER. 

by  the  strength  on  gross  section  is  the  efficiency  of  the  joint.  The 
safe  shearing  strength  of  rivets  may  be  taken  at  about  9000  pounds 
per  square  inch.  The  rivet-spacing  for  the  East  Jersey  pipe-line  was, 
for  example,  as  follows: 

Inches.  Inches.  Inches.   Inches. 

Nominal  size  of  pipe 48  48  48  36 

Thickness  of  sheets J  TV  f  J 

Size  of  rivets £  f  J  £ 

Circular  Seams. 

Rivet-pitch 1.5  1.8  20  1.5 

Lap  of  sheets 2  2f  2|  2 

Longitudinal  Seams  (double-riveted). 

Rivet-pitch 2.277  2.721  3.125  2.277 

Distance  between  rows ITV  iy3^  JA  riV 

Lap  of  sheets 3  $J  4  3 

In  the  72-inch  steel  pipe  at  Ogden,  Utah,  the.  longitudinal  joints 
were  double-strap  butt-joints,  triple-riveted,  similar  to  the  joints  used 
in  marine-boiler  practice.  The  circular  joints  were  double-riveted 
single-strap  butt-joints.  The  calculated  efficiency  of  longitudinal 
joints  is  from  85  to  87  per  cent.  The  stress  on  net  section  varies  from 
13,000  to  14,000  pounds  per  square  inch.  The  pipe  was  made  in 
sections  9  feet  2  inches  long,  each  section  consisting  of  a  single  plate. 
The  field-joints  were  power-riveted.* 

Steel  pipe-lines  are  usually  built  without  expansion-joints. 
Changes  of  temperature,  therefore,  produce  certain  longitudinal 
stresses  which  must  be  considered  in  designing  the  circular  joints  and 
in  making  connections  at  valves  and  other  points.  The  stress  per 
square  inch  on  gross  section  due  to  temperature  changes  is  given  by 
the  formula  of  Art.  577,  page  555.  For  steel,  c  =  about  .0000065 
and  E  =  30,000,000  pounds  per  square  inch.  If  the  pipe  is  buried, 
the  range  of  temperature  will  not  exceed  40  to  45  degrees,  so  that, 
assuming  the  pipe  laid  at  a  temperature  equal  to  the  maximum,  the 
greatest  stress  caused  by  a  reduction  of  temperature  will  be 

s  =  45  X  .0000065  x  30,000,000 
=  8800  pounds  per  square  inch  on  gross  area. 

Considering  the  self-adjustments  which  will  take  place  during  the  con- 

*  Trans.  Am.  Soc.  C.  E.,  1897,  xxxvm.  p.  258. 


WROUGHT-IRON  AND    STEEL   PIPE.  569 

struction  of  the  pipe,  the  stress  caused  by  temperature  changes  will 
doubtless  be  considerably  less  than  that  here  computed. 

If  the  pipes  are  exposed  for  any  great  distance,  expansion -joints 
become  necessary,  for  .the  consideration  of  which  reference  is  made 
to  the  next  chapter. 

594.  The  Locking-bar  Joint. — A  novel  form  of  longitudinal  joint 
which  appears  to  have  much  merit  is  what  is  known  as  the  locking- 
bar  joint,  used  recently  on  some  Australian  pipe-lines  (Fig.  146).  In 


Locking-  Section  of  pipe  Section  of  joint-ring, 

bar.  near  circular  joint. 

FIG.  146. — THE  LOCKING-BAR  JOINT. 

making  this  joint  the  plates  are  slightly  upset  at  the  edges,  then  in- 
serted in  the  grooves  of  the  bar  and  the  bar  pressed  down  upon  the 
plates  in  an  hydraulic  press.  The  pipes  are  then  tested,  and  if  found 
leaky  the  joints  are  usually  corrected  by  additional  work  in  the  press. 
No  calking  is  required.  Tljis  form  of  joint  has  proven  cheaper  than 
the  riveted  joint,  and  where  it  has  been  used  specifications  have  required 
its  efficiency  to  be  as  great  as  that  of  the  plates.  Tests  by  Prof.  Unwin 
have  shown  that  this  requirement  can  be  readily  met.  This  joint  pos- 
sesses a  very  considerable  advantage  over  the  riveted  joint  in  that  it 
forms  no  obstruction  to  the  flow  of  water  beyond  causing  a  slight  reduc- 
tion in  the  cross-section  of  the  pipe.  The  figure  also  illustrates  the 
joint-rings  for  the  circular  joints.  These  joints  are  made  with  lead 
as  for  cast-iron  pipes. * 

595.  Special   Details. — Changes  in  direction  are  usually  made  by 
forming  one  or  more  joints  at  a  small  bevel.      Two  or  three  standard 
bevels  of  small  angle  may  be  adopted,  and  any  desired  curve  made  by 
the    use    of  one    or    more    of  these  bevels.      Branches,    etc.,*  for  the 
ordinary  sizes  of  pipes,  are  usually  made  of  cast  iron  and  are  riveted 
or  bolted  firmly  to  the  steel  pipe.      Valves  are  joined  to  the  pipe  in 
a  similar  manner  by  means  of  cast-iron  flanges.      In  connecting  large 
mains  Mr.  Herschel  has  adopted  the  plan  of  using  several  small  cast- 
iron  flanged  connections,  an  arrangement  which  allows  the  use  of  small 
castings  and  small  valves.      Riveted  specials  are  sometimes  used  for 
large  pipes. 

596.  Coating  of  Steel  Pipe. — The  tar  coating  employed  for  cast-iron 
pipe  is  not  so  successful  when  applied  to  steel  or  wrought  iron,  but  the 

*  Eng.  News,  1898,  xxxix.  p.  373  ;  XL.  p.  423.     Eng.  Record,  1900,  XLI.  p.  178.     See 
also  use  of  this  joint  at  Lynchburg,  Va.,  Eng.  Record,  1906,  LIV.  p.  228. 


5/0  PIPES  FOR    CONVEYING    WATER. 

necessity  of  a  perfect  coating-  is  even  greater  in  this  case  on  account 
of  the  comparative  thinness  of  the  metal.  Some  form  of  asphalt  coat- 
ing has  usually  been  employed.  The  ordinary  method  of  applying 
the  coating  is  to  dip  the  pipe  in  liquid  refined  asphalt  heated  to  a  tem- 
perature of  280  to  350  degrees,  as  in  the  coal-tar  process.  A  second 
dipping  to  thicken  the  coat  is  often  used.  Various  mixtures  of  asphalt 
and  tar  have  been  tried,  but  with  no  better  results  than  with  the  pure 
asphalt. 

A  process  of  applying  asphalt  varnish,  known  as  the  Sabin  process, 
has  been  used  in  some  recently  constructed  pipe-lines  with  apparently 
more  success  than  has  accompanied  the  old  method.  In  this  process, 
the  pipe,  after  dipping,  is  baked  for  several  hours  at  a  temperature  of 
400  to  600  degrees,  thus  producing  an  enamel  coating. 

In  all  cases  the  pipe  must  be  thoroughly  cleaned  before  coating. 
The  specifications  for  the  Coolgardie  pipe-line  require  the  pipe  to  be 
cleaned  by  being  dipped,  first  in  dilute  sulfuric  acid,  and  then  in  a  bath 
of  lime-water.  The  coating  consists  of  Trinidad  asphalt  and  creosote. 
The  coating  of  the  Bundalier  pipe-line  is  composed  of  equal  parts  of 
asphalt  and  coal-tar. 

Still  another  form  of  coating  recently  used  is  known  as  '  *  mineral 
rubber  ' '  asphalt.  It  is  composed  of  asphalt,  but  the  process  is  secret. 
The  pipe  is  dipped  but  not  baked.  This  process  was  adopted  at  Min- 
neapolis in  1897,  and  has  been  used  in  several  other  important  works. 
The  results  so  far  appear  to  be  quite  promising. 

In  transportation  and  in  construction  in  the  field,  great  care  must 
be  exercised  to  avoid  injuring  the  coating.  Some  protective  covering 
of  pieces  of  old  carpet  or  canvas  should  be  used,  and  the  workmen 
required  to  wear  rubber  shoes.  The  field-joints  and  all  places  where 
the  coating  has  been  injured  should  be  coated  by  applying  with  a 
brush  some  kind  of  protective  paint.  Asphalt  dissolved  in  carbon 
bisulfide  (P.  &  B.  paint)  is  often  used,  but  the  fumes  from  it  are  very 
objectionable  to  the  workmen.  Various  other  asphalt  paints  or  var- 
nishes are  also  used  for  this  purpose. 

597.  Durability  of  Steel  Pipe. — Steel  pipe  coated  with  asphalt  has 
in  some  cases  been  reported  to  be  in  perfect  condition  after  a  lapse 
of  thirty  or  forty  years.  In  other  cases  corrosion  has  been  quite  rapid, 
so  that  the  life  of  the  pipe  has  been  short  as  compared  to  that  of  cast  iron. 
The  Rochester  wrought-iron  pipe  built  in  1873-5  nas  m  twenty-one 
years  required  a  little  repairing  by  means  of  patches  placed  on  the  out- 
side. During  this  time  eight  plates  out  of  a  total  of  14,000  have  been 
thus  repaired.  No  leaks  have  developed  at  riveted  joints.  The  Roches- 


WOODEN  PIPE.  571 

ter  pipe  was  coated  with  Trinidad  asphalt  and  coal-tar.  Mr.  Freeman 
in  estimating  the  cost  of  steel  pipe-lines  for  New  York  City  assumes 
their  life  at  fifty  years,  but  provides  for  their  cleaning  and  painting 
about  every  ten  years. * 


WOODEN   PIPE. 

598.  Advantages  of  Wooden  Pipe. — It  was  noted  in  the  introduction 
that  the  use  of  wood  for  water-mains  was  quite  universal  in  the  early 
days  of  water-works  construction,  and  that  this  material  was  subse- 
quently displaced  by  cast  iron.      The-use  of  wooden  pipe  under  certain 
conditions  has  now  again  reached  considerable  proportions  in  certain 
parts  of  the  country. 

In  general,  wooden  pipe  is  practically  adapted  to  those  locations 
where  transportation  of  iron  is  very  expensive  and  where  wood  is 
relatively  cheap.  When  properly  constructed,  wooden  pipe  is  very 
durable ;  it  is  not  subject  to  corrosion  by  electrolysis  nor  affected  by 
changes  of  temperature,  and  it  also  furnishes  good  protection  to  the 
water  against  cold  and  heat  in  exposed  locations.  It  possesses  an- 
other very  considerable  advantage  in  the  smoothness  of  the  interior 
and  in  the  fact  that  the  capacity  does  not  become  reduced  through  cor- 
rosion. The  special  field  for  wooden  pipe  is  for  low  pressures  and 
moderate  sizes,  where  a  metal  pipe,  if  used,  would  necessarily  have 
excessive  strength. 

599.  Bored  Pipe. — The  manufacture  of  bored  pipe  for  water-mains 
has  been  somewhat  revived  in  recent  years,  and  a  considerable  amount 
of   such    pipe   is   now  manufactured   under   the   name   of   ' '  improved 
WyckofTpipe."      The  pipe  is  made  from  solid  logs,  but  it  depends  for 
strength  upon  spiral  bands  of  flat  iron  which  are  wound  tightly  about 
it  from  end  to  end.      The  exterior  of  the  pipe  is  coated  with  pitch  as  a 
protection  to  the  bands.      The  joints  are  made  by  means  of  wooden 
thimbles  fitting  tightly  in  mortises  in  the  ends  of  the  pipe,  and,  in  lay- 
ing, the   sections   are   driven   together   by   means   of  a  wooden  ram. 
The  interior  surface  is  smooth  and  continuous.      The  pipe  is  made  in 
sections  8  feet  long,   and  in  sizes  from  2  to   17  inches  in  diameter. 
The  bands  are  spacecf  according  to  the  pressure.      Branch  connections 
are  made  by  means  of  cast-iron  specials  which  have  long  sockets  into 
which  the  wooden  pipe  is  driven.     A  considerable  amount  of  this  pipe  has 
been  used  in  recent  years.     It  is  very  durable  and  is  said  to  cost  some- 

*  Report  on  New  York's  Water-supply,  1900,  p.  320. 


572  PIPES  FOR    CONVEYING    WATER. 

what  less  than  cast   iron  where  the    transportation    charges  are  not 
excessive. 

600.  Stave-pipe. — The   necessities  of  water-carriage  in  the  West, 
and  the  expense  of  iron  pipe  in  that  region,  have  developed  a  very 
efficient  form    of  wooden-stave    pipe.      As  early  as   1874  Mr.   J.  .T. 
Fanning  built  such  a  pipe  at  Manchester,  N.  H.,  which  is  still  in  use, 
but  the  chief  development  of  this  type  of  construction  has  taken  place 
in  the  West  since  1883,  at  which  time  stave-pipe  was  first  extensively 
used  at  Denver. 

The  pipe  is  built  continuously  in  the  trench.  The  staves  are 
formed  with  radial  edges,  and  are  bound  tightly  together  by  means  of 
round  or  oval  bands  of  steel  or  iron,  spaced  and  sized  according  to 
the  pressure,  and  fastened  by  shoes  and  nuts.  The  general  form  of 
construction  and  method  of  building  will  be  clearly  understood  by  ref- 
erence to  Figs.  147  and  148.  The  latter  illustration  shows  also  the 
method  of  carrying  a  wooden  pipe  across  a  narrow  gorge. 

Two  types  of  stave-pipe  have  been  employed.  In  one  of  these, 
the  Allen  patent,  the  outside  and  inside  surfaces  of  the  staves  are  made 
concentric.  The  staves  are  made  to  break  joints,  and  the  end  joints 
are  made  tight  by  inserting  small  steel  plates  in  saw-kerfs  in  the  staves. 
In  the  other  form,  the  Durelle  patent,  polygonal  staves  1 6  to  20  feet 
long  are  used  which  have  a  slight  tongue  and  groove  formed  on  the 
edges.  The  staves  do  not  break  joints,  but  the  end  joint  is  made  by 
surrounding  the  pipe  by  a  layer  of  staves  4  feet  long.  The  former 
type  has  been  most  frequently  used. 

Stave-pipe  is  suited  to  pressures  up  to  about  100  pounds  per  square 
inch.  Above  this  limit  it  will  usually  be  less  economical  than  steel, 
as  the  bands  become  very  heavy  and  numerous.  Stave-pipe  has  been 
constructed  in  sizes  from  i  foot  up  to  9  feet  in  diameter.* 

60 1,  General    Requirements  for    Staves   and  Bands. — The    staves 
should  be  made  of  clear  stuff  and  be  somewhat  seasoned.      California 
redwood  and  Oregon  fir  have  been  most  frequently  employed.      The 
staves  should  be  thick  enough  to  prevent  percolation  and  not  deflect 
appreciably  between  bands.      In  practice  the  size  varies  from  about  I 
inch  by  4  inches  to  2^  by  8  inches. 

Bands  should  be  made  of  a  good  quality  of  soft  steel,  and  should  be 
upset  for  the  sake  of  economy.  They  should  be  thoroughly  coated 
with  asphalt  before  being  used.  They  must  be  of  such  a  size  and  so 
spaced  as  to  withstand  the  stresses  to  which  they  are  subjected,  prevent 

*  For  a  full  and  valuable  discussion  of  the  design  and  construction  of  stave-pipe 
see  paper  by  A.  L.  Adams  in  Trans.  Am.  Soc.  C.  E..  1899,  XLI.  p.  27. 


FIG.  147. — WOODEN-STAVE  PIPE. 


in 


in  £ 

g  » 

p  y 

w  z 

-  H 

<l  > 


K     O 
O     i» 

r 


WOODEN  PIPE.  577 

flexure  of  the  staves  sufficient  to  cause  leakage,  and  not  injuriously  crush 
the  fibers  of  the  wood.  To  resist  the  water-pressure  large  bands  and 
wide  spacing  will  in  general  be  most  economical,  but  the  size  is  lim- 
ited by  the  requirement  that  the  band  must  not  crush  the  wood  when 
fully  stressed,  and  the  spacing  must  not  exceed  a  certain  maximum. 

In  practice  the  thickness  of  staves  to  give  durability  and  prevent 
percolation  will  allow  a  maximum  spacing  of  10  to  12  inches  under 
light  pressures.  Under  any  considerable  pressure,  other  requirements 
will  govern  the  size  of  bands  and  the  spacing. 

602.  Size  of  Bands. — As  the  size  of  a  band  increases,  its  strength 
increases  as  the  square  of  the  diameter,  while  the  safe  pressure  upon 
the  wood  increases  only  as  the  first  power  of  the  diameter,  so  that  for 
each  case  a  definite  limit  exists  for  the  size  of  band  which  may  be 
used.  Experience  shows  that  the  width  of  contact  of  round  bands  with 
the  wood,  when  the  latter  is  compressed  within  safe  limits,  is  about 
equal  to  the  radius  of  the  band.  The  ultimate  crushing  strength  of  the 
wood  is  from  1000  to  2000  pounds  per  square  inch,  and  the  safe  stress 
is  usually  taken  at  from  600  to  750  pounds.  Mr.  Adams,  in  the  paper 
referred  to  on  page  518,  uses  a  value  of  650.  Adopting  this  figure 
and  letting  r  =  radius  of  band,  and  e  =  safe  pressure  per  lineal  inch 
of  band,  we  have  e  =  6$or.  Further,  let  5  =  safe  strength  of  band, 
.R  =  internal  radius  of  pipe,  and  /  =  thickness  of  pipe;  then 

S  =  (R  +  t)e  =  (R  +  i)6$0r (5) 

from  which  equation  the  size  of  band  is  determined.  A  factor  of  safety 
of  about  4  is  usually  employed. 

In  case  the  calculated  size  of  band  will,  by  the  formula  for  spacing 
given  in  the  next  article,  correspond  to  a  spacing  greater  than  10  or 
12  inches,  then  the  spacing  should  be  assumed  at  the  maximum  allow- 
able value  and  the  size  of  band  calculated  by  eq.  (6).  This  will  occur 
for  light  pressures  only.  Bands  less  than  f  inch  should  not  be  used. 

From  these  considerations  Mr.  Adams  has  made  up  a  table,  repro- 
duced in  Table  No.  76,  which  gives  a  suitable  size  of  stave  and  the 
maximum  size  of  band  for  different  diameters  of  pipe,  using  a  factor  of 
safety  of  about  4  for  the  bands.  Oval  bands  are  assumed  for  pipes 
20  inches  in  diameter  or  less,  in  order  to  secure  a  greater  proportionate 
area  of  contact.  For  the  10-,  12-,  22-,  and  3O-inch  pipes  the  bands 
used  cannot  be  stressed  to  their  full  working  value  without  crushing 
the  wood.  The  permissible  working  stress  given  is  such  as  will  give 
a  value  of  e  equal  to  6  5  or. 


578 


PIPES  FOR    CONVEYING    WATER. 


603.  Spacing  of  Bands. — The  size  being  determined,  the   spacing 
will  depend  upon  the  stresses.      These  are  from  three  sources: 

1.  The  initial  tension. 

2.  The  stress  due  to  water-pressure. 

3.  The  stress  due  to  the  swelling  of  the  wood. 

TABLE   NO.  76. 

ECONOMIC    PROPORTIONS    FOR    STAVE- PIPE   DESIGN  (ADAMS). 


Nominal 
Diameter 
of  Pipe. 
Inches. 

Stock  Sizes  for 
Staves. 

Thickness  of 
Finished 
Staves. 

Economic  Sizes 
of  Bands. 

Working-  Stress 
in  Band. 
S. 
Pounds. 

Factor  of  Safety 
in   Band. 

Oval. 

10 

li"  X  4" 

iA" 

A"  x  A" 

1255 

5.26 

12 
H 

4X4 
4X4 

1 

A  XA 

A  XA 

1475 
1650 

4-47 
4 

16 

2       X  6 

*A 

A  XA 

1650 

4 

18 

20 

2       X  6 
2       X  6 

if 
Jt 

*  ** 

Tff     X   Tff 

1650 
1650 

4 
4 

Circular. 

22 

2       X  6 

if 

I 

1508 

4.4 

24 

2       X  6 

if 

1650 

4 

27 

2       X  6 

iA 

1650 

4 

30 

2       X  6 

it 

2673 

4.4 

36 

2       X  6 

iA 

2950 

4 

42 

2       X  6 

if 

2950 

4 

48 

2       X  6 

«« 

2950 

4 

54 

2£     X   8 

*l 

4600 

4 

60 

3       X  8 

4 

4600 

4 

66 

3       X  8 

2T9* 

6600 

4 

72 

3       X   8 

2f 

6600 

4 

If,  after  a  pipe  is  filled  with  water,  the  bands  be  loosened  until  the 
water  begins  to  percolate  through  the  cracks,  the  stress  will  then  be 
due  to  (2)  only,  but  this  condition  is  impracticable  of  attainment.  In 
actual  practice  the  staves  are  more  or  less  seasoned  and  the  bands 
screwed  up  tightly  at  first.  The  wood  will  readily  swell  2  or  3  per 
cent,  which  is  an  amount  far  beyond  the  capacity  of  the  bands  to  allow 
by  virtue  of  their  elasticity  and  their  sinking  into  the  wood ;  so  that 
the  total  force  on  the  bands  is  approximately  equal  to  the  swelling- 
power  of  the  wood  (crushing-strength  of  saturated  wood)  plus  the  water- 
pressure.  The  swelling-power  of  the  staves  appears,  from  experiments 
by  Mr.  A.  C.  Henny,*  to  vary  from  50  to  200  pounds  or  more  per 
square  inch, — ordinarily  from  75  to  150  pounds.  Adams  assumes  100 
pounds,  and  this  is  probably  a  sufficiently  high  value. 

To  determine  the  spacing  we  have  then,  if  d  =  spacing  of  bands  in 


*  Trans.  Am.  Soc.  C.  E.,  1899,  vol.  XLI.  p.  76. 


WOODEN  PIPE.  579 

inches,  /  ==  water-pressure  per  square  inch,  and  ef  =  swelling-force  of 
wood  per  square  inch,  with  other  notation  as  on  page  523, 

5  =  pdR  +  e'td, 


.    .      ....      (6) 

In  this  formula,  5  is  the  safe  strength  of  the  band  as  determined 
by  the  application  of  eq.  (5).  The  size  of  the  band  and  its  working 
stress  may  also  be  taken  from  Table  No.  76.  If  the  spacing  as  found 
from  eq.  (6)  is  greater  than  the  maximum  allowable,  then  d  should  be 
assumed,  the  value  of  5  computed,  and  the  size  of  band  selected 
accordingly. 

For  large  sizes  and  high  pressures  the  term  e't  is  relatively  small 
and  a  formula  for  spacing  based  on  water-pressure  alone,  namely, 
£ 

d  =.  —=yy  is  sufficiently  accurate,  and  is  used  by  some  engineers.      For 
pK 

small  sizes  and  low  pressures  it  is  desirable,  however,  to  take  account 
of  the  swelling  action. 

It  is  to  be  noted  that  no  account  has  been  taken  of  initial  tension. 
It  has,  however,  been  assumed  that  the  stress  on  the  band  is  caused 
by  full  water-pressure  plus  the  swelling-power  of  the  staves,  and  this 
is  the  maximum  force  which  can  act  upon  the  bands. 

604.  Coupling-shoes.  —  The  coupling  of  the  bands  is  made  by  means 
of  a  malleable-iron  or  steel  shoe  closely  fitting  the  pipe,  and  of  a  strength 
equal  to  that  of  the  bands.      The  design  of  this  shoe  is  a  matter  of  con- 
siderable importance  and  some  difficulty.      It  should  be  so  made  as  to 
strain  the  bands  axially,  it  should  have  a  good  bearing  on  the  staves 
so  as  not  to  cause  undue  pressure,  and  it  should  be  convenient  and 
made  as  light  as  possible,   consistent  with  strength.      Two  forms  of 
shoes  are  illustrated  in   Fig.   149.      The  first  is  of  malleable  cast  iron, 
while  the  second  is  a  forged   shoe.      The  first  requires  a  forged  head 
on  the  band,  and  the  second  a  loop-eye.      The  pressure  between  shoe 
and   pipe  is  quite  uniform  in  both  these   forms,  which  is  not  true  of 
some  that  have  been  used.    Other  forms  are  illustrated  in  Mr.  Adams's 
paper. 

605.  Specials.  —  Stave-pipe  can  readily  be  built  to  a  curvature  of 
from  200  to  300  feet  radius  by  springing  the  staves  into  place.      Con- 
nections are  usually  made  by  means  of  castings  with   deep  bells,  into 
which  the  pipe  is  built  and  calked  with  oakum  and  paint.      Variations 
in  diameter  are  made  by  the  use  of  tapered  staves.      Repairs  can  very 
readily  be  made  in  this  kind  of  pipe. 


580 


PIPES  FOR    CONVEYING    WATER. 


606.  Leakage  and  Durability  of  Wooden  Pipe. — Tests  of  pipe-lines 
have  shown  in  some  cases  practically  no  leakage.  In  others,  a  slight 
leakage  has  been  observed  which,  including  evaporation  from  the 


BOTTOM   VIEW 

ia-      ai 

B-B  A-A 

FIG.  149. — COUPLING-SHOES  FOR  WOOD-STAVE  PIPE. 

(From  Trans.  Am.  Soc.  C.  E.,  vol.  XLI.) 

surface,  has  amounted  to  from  .053  to  .086  gallon  per  square  foot  per 
day.  Mr.  Henny  considers  that  a  leakage  of  .05  gallon  per  square 
foot  per  day  is  a  safe  allowance  for  exposed  pipes. 

The  durability  of  wooden  pipe  varies  greatly  under  different  condi- 
tions. Where  the  pipe  is  constantly  in  service  and  under  a  considerable 
pressure  the  wood  is  generally  kept  sufficiently  saturated  to  prevent 


MATERIALS  EMPLOYED  FOR    WATER-PIPE.  581 

decay.  Many  old  wooden  water  mains  in  various  cities  have  been  found 
perfectly  sound  after  sixty  or  seventy  years  of  use.  The  conditions  are, 
however,  not  so  favorable  for  the  usual  wooden  stave  conduit,  as  the 
pressures  are  generally  not  great  and  the  durability  of  some  such  pipe 
lines  has  been  much  less  than  expected.  To  some  extent  this  seems 
to  be  due  to  the  collection  of  air  along  the  upper  portion  of  the  pipe, 
thus  permitting  the  wood  to  become  partially  dry.  The  quality  of  the 
material  is  also  of  much  significance.  Wood  is  particularly  advantageous 
where  salt  water  is  encountered.  The  steel  bands  are  subject  to  some 
corrosion,  but  the  form  of  cross-section  is  favorable  and  the  relative 
deterioration  is  generally  quite  slow. 

OTHER   MATERIALS  EMPLOYED    FOR  WATER-PIPE. 

607.  Cement  Pipe.  —  Pipe  made  by  lining  a  core  of  wrought  iron 
inside  and  out  with  cement  mortar  has  been  much  used  in  the  eastern 
part  of  the  United  States,  but  is  now  employed  in  very  few  places. 
It  is  still  reported  to  give  satisfactory  service  in  some  cases,  but  it  has 
generally  been  abandoned  for  cast  iron.     There  is  great  difficulty  in 
maintaining  the  cement  coating  intact,  and  if  it  is  broken  the  iron  core 
soon  corrodes.     Its  life  is  in  many  places  not  over  ten  years. 

For  large  conduits,  reinforced  concrete  may  often  be  employed  to 
advantage.  It  has  also  been  used  to  some  extent  for  pressure  pipes, 
especially  in  France,  where  it  has  been  successfully  employed  for  pres- 
sures up  to  300  feet.  In  this  country  it  has  been  tried  only  to  a  limited 
extent  and  without  great  success.*  The  use  of  reinforced  concrete  for 
conduits  is  further  discussed  in  the  next  chapter. 

608.  Vitrified-clay  Pipe  has  been  employed  in  a  few  places  for  con- 
duits.    It  is  cheap,  indestructible,  and  when  the  joints  are   carefully 
made  the  leakage  is  very  small.     It  is  generally  used  under  no  pres- 
sure, but  in  one  or  two  instances  has  been  designed  to  carry  consider- 
able pressures.     Vitrified  pipe  has  recently  been  recommended,  in  a 
report  to  the  city  of  Oakland,  for  salt-water  mains  to  furnish  water  for 
street-sprinkling,  f     It  was  thought  it  could  easily  be  made  to  with- 
stand 100  pounds  pressure.     The  form  of  joint  was  to  be  of  strips  of 
burlap  dipped  in  asphalt,  which  form  has  been  well  tested  under  40  to 
50  pounds  pressure.    At  Florence,  Colorado,  a  /-mile  conduit  of  1 2-inch 
vitrified  pipe  has  been  built.     It  is  not  under  pressure.     Vitrified  pipe 
has  also  been  extensively  used  at  Little  Falls  and  at  Amsterdam,  N.  Y., 

*  See  paper  by  C.  W.  Smith,  Proc.  Am.  Soc.  C.  E.,  August,  1907,  p.  581.    Also 
Eng.  News,  1898,  xxxix.  p.  170.        t  Eng.  News,  1899,  XLII.  p.  149. 


582  PIPES  FOR   CONVEYING    WATER. 

a  length  of  5.63  miles  having  been  constructed  at  the  former  place. 
A  very  considerable  saving  was  thus  secured.  Deep  sockets  were  used 
and  the  joints  carefully  made  by  means  of  jute  soaked  in  Portland 
cement,  with  which  material  the  joint  was  thoroughly  filled  to  within 
•J-  inch  of  the  outside.  The  remainder  of  the  space  was  filled  with 
Portland-cement  mortar.  The  cost  of  the  Little  Falls  conduit  of  12- 
to  2O-inch  pipe  was  about  $1.50  per  foot,  which  was  about  one-half 
the  cost  of  cast-iron  pipe. 

609.  Materials  for  Service-pipes. — Service-pipes,  or  pipes  for  con- 
ducting water  to  individual  consumers,  are  made  of  a  considerable 
variety  of  materials.  Uncoated  iron  pipe,  or  pipe  coated  only  with 
tar,  is  not  serviceable  for  such  small  sizes  (usually  f  to  i^  inches  in 
diameter),  as  even  a  small  amount  of  tuberculation  would  completely 
clog  up  the  pipe.  Galvanized,  tin-lined,  lead-lined,  and  cement-lined 
iron  pipe  are  widely  used,  but  the  most  common  is  lead  pipe.  Lead 
pipe  is  practically  indestructible,  but  rather  expensive  and  heavy  for 
high  pressures.  In  some  places  it  cannot  be  used  with  safety  on 
account  of  the  danger  of  lead  poisoning.  Certain  waters  only  will 
attack  lead  to  a  sufficient  extent  to  render  its  use  dangerous,  but,  de- 
spite the  study  that  has  been  put  upon  the  subject,  it  is  not  yet  fully 
known,  without  actual  experiment,  what  effect  various  classes  of  waters 
will  have. 

Recently  the  Massachusetts  Board  of  Health  has  investigated  this 
question  by  reason  of  several  cases  of  lead-poisoning  that  have  occurred 
in  that-  State.  *  Thirty  cases  were  especially  studied  in  which  lead 
pipe  was  largely  used.  In  general  it  was  found  that  waters  having 
the  greatest  amount  of  dissolved  solids  and  hardness  dissolve  the  least 
amount  of  lead,  and  that  the  active  agents  causing  the  solution  of  the 
lead  are  oxygen  and  carbonic  acid.  The  latter  is  characteristic  of  soft 
waters.  In  fifteen  towns  with  ground-water  supplies  the  average 
amount  of  lead  ranged  from  .0055  to  .1899  part  per  100,000  with 
pipes  in  ordinary  use,  and  from  .0108  to  8.38  parts  when  the  water 
had  stood  in  the  pipes.  Surface-waters  in  fourteen  towns  averaged 
similarly  from  .0031  to  .0788,  and  from  .0099  to  .3921  parts  respec- 
tively. In  four  cities  with  ground-water  supplies,  cases  of  lead-poison- 
ing were  prevalent,  and  in  these  four  cases  the  lead  averaged  o.  2  part, 
after  the  -water  had  stood  several  hours  in  the  pipes.  No  cases  of 
poisoning  occurred  with  surface  supplies.  Experiments  on  galvanized 
iron  and  plain  iron  showed  more  action  than  on  lead,  but  with  tin  the 
corrosion  was  very  little. 

*  Report  for  1898,  p.  539. 


LITERATURE.  583 

As  to  the  amount  of  lead  which  will  give  trouble  it  is  known  that 
continuous  use  of  water  containing  .05  part  per  100,000  has  caused 
serious  injury  to  the  health.  Zinc  is  not  dangerous  in  the  amounts 
likely  to  be  present  and  galvanized  iron  pipe  is  much  used. 

Cement-lined  pipe  is  quite  largely  used  in  the  East,  but  in  some 
places  it  does  not  prove  to  be  very  durable  for  the  same  reason  as  given 
in  Art.  607.  It  has,  however,  given  good  service  in  many  cities.  Tin- 
lined  pipe  is  now  being  used  to  some  extent.  It  is  quite  expensive,  but 
the  experience  with  it  so  far  indicates  that  it  is  very  durable. 

Statistics  relating  to  the  material  employed  in  new  services  in  Massa- 
chusetts cities  and  towns  show  that  lead  or  lead-lined  pipes  are  used  in 
26  cities  and  towns,  cement-lined  pipes  in  43  places,  galvanized  iron 
pipes  in  77  places  and  tin-lined  pipes  in  6  places.  Much  trouble  has 
been  reported  from  the  rusting  of  galvanized  iron.* 

LITERATURE. 

(See  also  references  of  Chapter  XXV.) 
CAST-IRON  PIPE. 

1.  Jamieson.     The  Internal  Corrosion  of  Cast-iron  Pipe.     Proc.  Inst.  C.  E., 

1880-81,  LXV.  p.  323. 

2.  Rowland.     Water  Pipes.     Proc.  Eng.  Club  Philadelphia,  1886,  vi.  p.  55. 

3.  Russell.     Thickness  of  Water-pipe.     Jour.  Assn.  Eng.  Soc.,   1889,  vm. 

p.  100. 

4.  Cement-joints   for   Cast-iron   Water-mains.     Eng.  News,    1892,   xxvin. 

P-  235- 

5.  Brackett.     Uniformity  in  Designs  for  Special  Castings.     Jour.  New  Eng. 

W.  W.  Assn.,  1893,  vm.  p.  78;  Eng.  News,  1893,  xxix.  p.  579. 

6.  Duane.     The  Effect  of  Tuberculation  on  the  Delivery  of  a  48-inch  Water- 

main.     Trans.  Am.  Soc.  C.  E.,   1893,  xxvm.  p.  26.     Valuable  dis- 
cussion. 

7.  Life  of  Cast-iron  Water-pipe  at  St.  John,  N.  B.     Eng.  News9  1894,  xxxi. 

p.  15.     Experience  with  wooden  joints. 

8.  Lewis.     Cast-iron  Water-pipe.     Cassier's  Mag.,  1895,  vm.  p.  17. 

9.  Garrett.     Making  Cast-iron  Pipe.     Jour.  New  Eng.  W.  W.  Assn.,  1896, 

xi.  p.  27. 

10.  Coating  of  Cast-iron  and  Steel  Riveted  Pipe.     Report  of  Com.  of  Am. 

Soc.  of  Munic.  Imp.,  Mun.  Eng.,  1897,  xm.  p.  280. 

11.  Wiggin.     The  Manufacture   and    Inspection    of    Cast-iron  Pipe.      Jour. 

Assn.  Eng.  Soc.,  1899,  xxn.  p.  209. 

12.  Brackett.     Water-pipe  on   the    Metropolitan  Water-works.      Jour.   New 

Eng.  W.  W.  Assn.,  1899,  xm.  p.  325. 

13.  Murdoch.     Wooden  Joints  in  Cast-iron  Water-mains.     Jour.  New  Eng. 

W.  W.  Assn.,  1900,  xv.  p.  34. 

14.  Forsheimer.     The  Strength  of  Large  Pipes.     Zeit.  Oest.  Ing.  u.  Arch. 

Ver.,  Feb.  26,  1904. 

*  Report  Mass.  Board  of  Health,  1905,  p.  197. 


584  PIPES  FOR   CONVEYING    WATER. 

15.  Standard  Specifications  for  Cast  Iron  Pipe  and  Special  Castings.    Report 

of  Committee.     Jour.   New  Eng.  W.  W.  Assn.,  Dec.,    1902,  Mch. 
1903  ;  Eng.  Record,  1902,  XLVI.  p.  245. 

1 6.  Conrad.     Some  Observations   on  Cast-iron    Pipe    Specifications.     Jour. 

New  Eng.  W.  W.  Assn.,  Mch.,  1907. 

(For  references  to  methods  of  removing  incrustation,  see   Literature  of 
Chapter  XXIX.) 

STEEL   PIPE. 

1.  de  Varona.     Report  on  the  Use  of  Cast  Iron,  Wrought  Iron,  and  Steel 

(for  the  Brooklyn  Conduit).     Proc.  Am.  W.  W.  Assn.,  1894.  p.  181. 

2.  The    Specifications   for  Riveted   Steel  Pipe,    Cambridge,    Mass.      Eng. 

Record,  1895,  xxxi.  p.  97. 

3.  The  Specifications  for  the  New  Bedford  Force  Main.     Eng.  Record,  1896, 

xxxni.  p.  293. 

4.  Cast-iron  vs.  Steel  Pipe.     Eng.  Record,  1896,  xxxm.  p.  349.     Compari- 

son of  cost. 

5.  Clarke.     The  Distortion  of  Riveted  Pipe  by  Backfilling.      Trans.  Am. 

Soc.  C.  E.,  1897,  xxxvin.  p.  93. 

6.  Kuichling.     The  Joints  of  Riveted  Water-pipe.     Lecture  at  Rensselaer 

Poly.  Inst.     Eng.  Record,  1899,  XL.  p.  33. 

7.  Hastings.     Use  of  Steel  for  Water-mains.     Jour.  New  Eng.  W.  W.  Assn., 

1899,  xm.  p.  314. 

8.  Sabin.     Experiments  on  the  Protection  of  Steel  and  Aluminum  Exposed 

to  Water.     Trans.  Am.  Soc.  C.  K,  1900,  XLIII.  p.  444. 

9.  Asphalt  Coatings  for  Water-pipe.     Eng.  News,  1900,  XLIII.  p.  331. 

10.   Freeman.     Construction,  Cost,   and  Water-carrying   Capacity  of   Large 
Steel  Conduits.     Report  on  New  York's  Water-supply,  1900,  p.  320. 

WOODEN  PIPE. 

1.  Fanning.     A  Water-conduit  under  Pressure.     Trans.  Am.   Soc.  C.  E., 

1876,  vi.  p.  69.     Description  of  the  Manchester  wood-stave  pipe. 

2.  Henny,     Wooden-stave  Pipe  vs.  Riveted  Pipe.     Jour.  Assn.  Eng.  Soc., 

1898,  xxi.  p.  239. 

3.  Wyckoff  Pipe  used  in  the   Water-works   of   North  Tonawanda.     Eng. 

Record,  1898,  xxxvm.  p.  515. 

4.  Wells.     Improved  Wyckoff  Pipe.     Jour.  New  Eng.  W.  W.  Assn.,  1899, 

xm.  p.  288. 

5.  Adams.     Stave  Pipe  :  Its  Economic  Design  and  the  Economy  of  its  Use, 

Trans.  Am.  Soc.  C.  E.,  1899,  XLI.  p.  27. 

6.  Henny.      Nine-foot  Wood-stave  Pipe,  Floriston  Pulp  and   Paper   Co., 

Floriston,  Cal.     Eng.  News,  1900,  XLIV.  p.  235. 

7.  Allen.     The  Wood-stave  Conduit  for  the  Water-supply  of  Atlantic  City. 

Jour.  New  Eng.  W.  W.  Assn.,  Dec.,  1904. 

8.  Birkinbine.     Some  Applications  of  Wooden-stave  Pipe.     Describes  Pipe 

at  Johnstown,  Pa.     Proc.  Eng.  Club  Phil.,  Jan.,  1905. 

9.  The   Pipe  Line  of  the  New  Gravity  Water-supply  of  Lynchburg,  Va. 

Consists  of  wood,  cast-iron  and  lock-bar  steel  pipe.     Eng.  Record, 
1906,  LIV.  p.  228. 

10.  Adams.     Additional  Information  on  the  Durability  of  Wooden    Stave- 

pipe.     Trans.  Am.  Soc.,  C.  E.,  1907,  LVIII.  p.  65. 


LITERATURE.  585 


VITRIFIED   CLAY   PIPE. 

1.  Babcock.     The  Use  of  Salt-glazed  Vitrified  Pipe  in  Water-works  Con- 

struction.     Eng.  Record,  1888,  xvn.  p.  361. 

2.  Notes  on  Vitrified-pipe  Conduit  at  Little  Falls,  N.  Y.     Eng.  News,  1895, 

xxxiv.  p.  283. 

3.  Maury.     Tests  of  the  Tightness  of  a  Vitrified  Earthenware  Water-conduit. 

Eng.  News,  1896,  xxxv.  p.  341. 

4.  Miller.     Report  on  Proposed  Salt-water  Street-sprinkling  Plant  at  Oak- 

land, Cal.     Eng.  News,  1899,  XLII.  p.  149.     Relates  to  the  use  of 
vitrified  pipe. 

5.  Tests  of  Asphalt  Joints  of  Vitrified  Pipe.     Eng.  Record,  1899,  XL.  p.  94. 

6.  Garrett.     Florence,  Col.,  Water-works.     Eng.  Record,  1900,  XLI.  p.  147. 

Describes  use  of  vitrified  pipe. 

7.  Johnson.      The  Hartford  Vitrified  Water-Conduit.     Eng.  Record,  1901, 

XLIII.  p.  30. 

SERVICE-PIPES. 

1.  Service-pipes.     Jour.  New  Eng.  W.  W.  Assn.,  1891,  p.  22.    A  discussion. 

2.  Chace.     Service-pipes,  Defects  and  the  Remedy.     Jour.  New.  Eng.  W.  W. 

Assn.,  1897,  xii.  p.  41. 

3.  Clark.     The  Action  of  Water  upon  Lead,  Tin,  and  Zinc.     Report  Mass. 

Board  of  Health,  1898,  p.  541.      See  also  reports  of  subsequent 
years  for  much  additional  information. 

4.  Forbes.     Cement-lined  Service-pipes.      Jour.  New  Eng.  W.  W.  Assn., 

1900,  xv.  p.  44. 

5.  Smith  and  Chaplin.     Treatment  of  Moorland  Water  to  Prevent  Action 

upon  Lead  Pipes.     Paper  before  Brit.  Assn.  W.  W.  Engrs.     Eng. 
Record.  1904,  L.  p.  187. 


CHAPTER   XXV. 
CONDUITS   AND   PIPE-LINES. 

610.  Where  the  source  of  supply  is  at  a  considerable  distance  from 
the  place  of  consumption  the  design  and  construction  of  the  necessary 
works  for  conducting  the  water  is  a  matter  of  great  importance  and 
demands  special  consideration.      Usually  a  distant  source  is  at  a  higher 
elevation  than  the  city  to  be  served,  so  that  it  will  be  possible  to  con- 
vey the  water  partly  or  wholly  by  gravity.     In  many  cases,  however,  a 
part  or  the  whole  of  the  water  will  require  pumping,  so  that  the  design 
will  also  involve  a  study  of  possible  pumping  arrangements.      It  will 
usually  be  necessary  to  consider  several  designs  based  upon  different 
locations  and  often  upon  different  types  of  conduits.      In  determining 
upon  the  dimensions  of  a  large  conduit  the  utmost  care  should  be  taken 
in  selecting  the  coefficient  to  be  used  in  the  hydraulic  formulas  em- 
ployed. 

611.  Classes  of  Conduits, — Conduits   are  divided  into   two   general 
classes:   (i)  those  in  which  the  water-surface  is  free  and  the  conduit 
therefore  not  under  pressure,  and   (2)   those  flowing  under  pressure. 
To  the  first  class  belong  open   canals,  flumes,  aqueducts,    and   usually 
tunnels,  and  to  the  latter  belong  pipe-lines  of  iron,   steel,   wood,   or 
other  material  capable  of  resisting  hydraulic  pressure,  and  sometimes 
tunnels.      Conduits   of  the  first  class   must  obviously  be   constructed 
with  a  slope  equal  to  that  designed  for  the  water-surface,  or  equal  to 
the  hydraulic  gradient.      This  will  be  a  very  light  and  uniform  slope, 
and  such  conduits  will  therefore  often  require  in  their  construction  long 
detours  to  avoid  hills  and  valleys,  or  resort  must  be  had  to  high  bridges, 
embankments,  cuttings,  or  tunnels.      Conduits  of  the  second  class  may 
be  constructed  at  any  elevation  below  the  hydraulic  grade-line,  but  if 
built  above  they  must  be  arranged  to  act  as  siphons.      The  selection 
of  the  form  of  conduit  is   principally  a  question   of  economy,  and  in 
this  respect  topography  will  largely  govern,  but  consideration  will  also 

586 


CA  PA  CI T  Y—L  O  CA  TION.  587 

be  given  to  various  advantages,  such  as  are  mentioned  in  the  following 
discussion. 

612.  Capacity  of  Conduits. — Where  the  conduit  is  long,  sufficient 
storage  capacity  is    usually  provided  in    the  vicinity  of  the   city    to 
equalize  the  demand  over  several  days  or  weeks,  so  that  the  capacity 
of  the  conduit  may  be  based  on  the  average  monthly  or  seasonal  con- 
sumption.     The   extent  to  which   provision   should  be   made   for  the 
future  depends  much  upon  the  type  of  conduit.      The  question  must  be 
settled  in  accordance  with  the  principles  laid  down  in  Chapter  XI.      In 
the  case   of  a  masonry  conduit  the.  expense  of  additional  capacity  is 
relatively  small,  so   that  it  will  be  economical  to  provide  for  a  long 
period  in   the  -future,  such   as  thirty  or  forty  years.      Very  often  the 
capacity  should  be  made  equal  to  that  of  the  watershed  drawn  upon. 
In  the  case  of  pipe  conduits   a  much  less  liberal  provision  should  be 
made  for  the  future,  as  the   expense  of  additional   capacity  is  propor- 
tionately much  greater. 

613.  Single  or  Double  Conduits. — Security  against  the  interruption 
of  the  supply  demands  either  that  there  be  two  conduits,  or  that  there 
be  sufficient  storage  capacity  at  the  city  end  to  allow  the  shutting  off 
of  the  supply  to  permit  of  any  repairs  which  may  be  needed.      The 
latter  method  will  usually  be  the  cheaper  except  for  very  short  lines. 
The  storage  capacity  necessary  to  allow  of  repairs  will  vary  from  three 
to  four  days'  consumption  in  the  case  of  small  pipe-lines  easy  to  repair, 
up  to  ten  or  fifteen  days'   supply  for  large  aqueducts.      The  amount  of 
storage   considered   necessary  for   this   contingency   should   never   be 
drawn  upon  for  other  purposes.      If  a  pressure  conduit  is  used  and  a 
double  line  is  considered  the  most  economical,  or  if  the  second  line  is 
built  subsequently  to  provide  added  capacity,  the  two  lines  should  be 
connected  at  frequent  intervals.      A  section  of  either  can  then  be  shut 
off  and  the  supply  carried  for  a  short  distance  in  one  pipe,  which  will 
result  in  but  a  small  increase  in   the  total  head   consumed  or  a  small 
decrease   in   total   flow.       Where   a   single   conduit    is    deemed    most 
economical  for  the  greater  portion,  it  may  still  be  advisable  to  build  a 
double  line  at  certain  points  where  a  breakage  would  be  a  very  serious 
matter,  as  at  river  crossings,  etc. 

614.  Location  of  Conduits. — The  location  of  a  conduit  is  a  matter 
requiring  much  skill  and  judgment.      It  involves  the  question  of  avail- 
able slope  or  hydraulic  gradient,  cost  of  conduits  of  different  forms  and 
sizes  and  built  of  different  materials,  and  frequently  the  cost  of  pump- 
ing.     In  the  matter  of  slope  there  may  be  sufficient  to  enable  the 


588  CONDUITS  AND    PIPE-LINES. 

water  to  be  conducted  entirely  by  gravity,  or  pumping  may  be  required 
at  one  or  more  points. 

In  the  case  of  conduits  not  under  pressure,  if  the  total  head  is 
closely  limited,  then  the  slope  must  be  maintained  nearly  uniform 
and  a  location  found,  if  possible,  which  will  support  the  aqueduct  at 
the  desired  elevation.  A  proper  balance  must  be  obtained  between  a 
circuitous  route  avoiding  high  crossings,  and  a  more  direct  route  which 
is  more  expensive  per  mile.  Usually  two  or  more  possible  routes  will 
need  to  be  examined  in  detail  and  comparative  estimates  made.  If 
the  available  head  is  large,  then  a  more  economical  location  can  prob- 
ably be  made,  as  the  slope  can  be  varied  to  a  considerable  extent  in 
order  to  best  fit  the  ground,  and  can  also  be.  made  steep  so  as  to  give 
small  sizes.  If  the  country  falls  more  rapidly  than  is  permissible  for 
the  conduit,  then  the  water  may  be  let  down  at  intervals  in  special  forms 
of  construction  designed  for  the  purpose. 

The  location  of  pressure  conduits  is  comparatively  simple.  For  them 
a  more  direct  line  can  be  adopted,  but  at  the  same  time  low  pressures 
are  to  be  desired.  There  should  be  as  few  summits  •  and  depressions 
as  practicable,  and  small  sags  should  be  avoided.  To  provide  oppor- 
tunity for  easy  regulation  of  the  pressure  it  is  desirable  that  the  conduit 
approach  close  to  the  hydraulic  grade-line  at  occasional  intervals,  as 
more  fully  explained  in  Art.  629. 

Tunnels  may  be  constructed  at  the  grade-line  and  hence  flow  free, 
or  they  may  be  built  at  a  lower  elevation  and  flow  under  pressure. 
Usually  the  former  will  give  the  shorter  and  cheaper  tunnel,  but  in 
some  cases  it  is  expedient  to  build  tunnels  at  a  greater  depth,  as  in  the 
Croton  aqueduct,  where  7  miles  of  tunnel  is  under  a  pressure  of  about 
55  pounds,  the  chief  purpose  being  to  avoid  interference  with  valuable 
property. 

Long  conduits  usually  include  both  masonary  aqueducts  and  pipe- 
lines, each  class  being  used  where  most  suitable.  The  former  is  used 
as  a  rule  where  the  ground  lies  near  or  above  the  hydraulic  grade-line, 
and  the  latter  where  it  lies  below  for  any  considerable  distance.  High 
and  long  aqueduct  bridges  are  no  longer  built,  a  pressure  conduit 
being  substituted,  which  may  follow  the  ground-profile  closely.  How- 
ever, as  the  transition  from  open  to  pressure  conduits  involves  some 
additional  details,  it  will  often  be  cheaper  to  support  the  former  on 
bridges  where  the  height  is  but  moderate.  Where  pumping  is  required 
the  expense  of  raising  water  must  be  considered  in  fixing  upon  the  size 
and  slope  of  the  conduit.  In  the  case  of  a  pipe  conduit  the  slope  or 
head  consumed  involves  only  the  question  of  size,  and  the  proper  size 


CANALS.  589 

to  make  the  total  cost  a  minimum  can  be  quite  easily  determined,  as 
shown  in  Art.  632.  With  an  open  conduit,  however,  the  topography 
will  very  largely  determine  the  slope  and  therefore  the  size. 

The  proper  location  of  a  conduit  requires  full  and  careful  surveys, 
including  numerous  borings  and  test-pits  to  determine  the  character  of 
the  material.  The  maps  of  the  United  States  and  various  State  geo- 
logical surveys  are  of  the  utmost  help  in  this  connection. 

CANALS. 

615.  Use  of  Canals. — The  open  canal  is  not  often  used  for  conveying 
water  for  city  use,  but  for  irrigation  purposes  it  is  the  common  form  of 
conduit.      For  the  former  purpose  it  has  several   objections,    such  as 
loss  of  water  by  percolation  and  evaporation,  exposure   of  water  to 
pollution  from  surface  drainage  and  otherwise,  and  exposure  to  summer 
heat,  which  not  only  warms  the  water  but  promotes  vegetable  growth. 
In  irrigation-canals  the  seepage  often  amounts  to  I  or  2  vertical  feet 
per  day,   an  amount  which  would  scarcely  be  permissible  in  a  city 
water- works  conduit,  where  a  large  expense  has  been  put  upon  storage- 
reservoirs,   and,  as  is  often  the  case,  where  the  total  capacity  of  the 
watershed  is  nearly  reached.      However,  where  a  canal  can  be  con- 
structed with  little  cutting  or  embankment,  and  where  the  material  is 
nearly  impervious,  it  may  be  the  best  form  of  construction. 

If  the  material  is  porous,  it  would  probably  be  better  to  adopt  the 
covered  masonry  conduit  than  to  incur  a  large  expense  in  constructing 
a  puddle  or  concrete  lining  to  a  canal.  A  very  favorable  location  for 
an  open  canal  is  where  a  stream-bed  can  be  made  into  a  canal  to  carry 
water  from  one  reservoir  to  another  lower  down  the  valley.  In  this 
case  there  will  usually  be  no  loss  by  seepage,  but  rather  a  gain  by  infil- 
tration of  ground-water.  In  side-hill  work,  or  in  country  of  any  diffi- 
culty, the  masonry  aqueduct  will  likely  be  the  cheaper  form  of  con- 
struction. For  very  large  quantities  of  water  the  economy  of  canals 
will  be  more  pronounced.  In  considering  the  adoption  of  a  canal  the 
possible  pollution  of  the  water  should  be  carefully  considered. 

616.  Slopes  and  Velocities. — If  the  available  head  permits,  the  most 
economical  slope  will  be  such  as  will  give  the  maximum  permissible 
velocity  for  the  material   and   therefore  the   minimum   cross-section. 
Topography  may  require  the  use  of  a  much  less  slope  than  this,  but 
a  greater  slope  cannot  be  used  without  danger  of  erosion,    or  an  in- 
creased cost  in  protection  by  paving  or  otherwise.      If  the  slope  of  the 
ground  is  too  great,  then  the  fall  may  be  concentrated  at  certain  points 


59°  CONDUITS  AND   PIPE-LINES* 

where  special  precautions  are  taken.  With  a  small  available  head  the 
velocity  will  be  low  and  the  section  will  have  to  be  made  large  to  cor- 
respond with  the  low  velocity. 

The  allowable  velocities  for  unprotected  canals  vary  from  about  I  £ 
to  2  feet  average  velocity  for  light  sandy  soils,  2\  to  3  feet  for  ordinary 
firm  soils,  and  3  to  4  feet  for  hard  clay  and  gravel.  In  rock  or  hard- 
pan  5  to  6  feet  may  be  allowed.  A  velocity  of  2  to  3  feet  per  second 
is  sufficient  to  prevent  silt  deposits  and  the  growth  of  weeds. 

The  velocity  and  discharge  for  any  given  slope  and  cross-section  is 
calculated  from  Kutter's  formula.  In  using  this  formula  the  selection 
of  a  proper  value  of  n  is  a  matter  of  much  uncertainty.  For  unlined 
channels  it  is  usually  taken  at  .020  to  .025  (see  Chapter  XII).  If 
vegetation  is  allowed  to  accumulate  in  the  canal,  a  large  allowance 
must  be  made  for  increased  resistance  caused  thereby. 

617.  Cross-sections. — The  cross-section  of  a  canal  is  usually  trape- 
zoidal in  form.  For  any  given  side  slope  the  trapezoidal  form  giving 
the  greatest  hydraulic  radius,  and  hence  the  most  economical  form  as 
regards  slope,  is  one  in  which  the  sides  and  bottom  are  tangent  to  a 
circle  whose  center  is  at  the  water-surface.  The  hydraulic  mean 
radius  of  such  a  section  is  one-half  the  depth  of  the  water.  The  side 
slope  giving  a  maximum  value  for  the  radius  is  60  degrees  with  the 
horizontal,  and  the  water-section  would  be  one-half  a  regular  hexagon, 
but  such  a  section  could  not  be  constructed  except  in  very  stable 
ground.  For  a  rectangular  section,  or  one  with  vertical  walls,  the 
width  should  be  twice  the  height.  The  hydraulic  radius  of  the  rectan- 
gular section  is  0.355  V-^.  and  of  the  semihexagonal  section  is  .38  V~A, 
where  A  is  the  area  of  cross-section.  The  section  having  the  least 
water-surface  is  the  triangle,  and  the  best  slope  of  the  sides  is  45 
degrees. 

The  sections  above  described  will  give  a  minimum  of  excavation, 
but  are  suitable  only  for  small  canals.  For  large  canals  the  material 
will  be  more  economically  handled  if  the  section  is  made  somewhat 
wider  and  shallower.  Furthermore,  if  the  canal  is  made  partly  by 
excavation  and  partly  by  embankment,  and  if  the  excavated  material 
is  suitable  for  embankment  construction,  the  amount  of  excavation  will 
decrease  as  the  width  of  channel  increases.  Too  wide  and  shallow  a 
channel  is,  however,  not  desirable,  as  the  velocity  will  be  diminished, 
vegetable  growth  will  be  more  troublesome,  and  the  reduction  of  sec- 
tion due  to  ice  will  be  proportionately  greater.  Very  large  canals  are 
sometimes  made  ten  to  fifteen  times  as  wide  as  deep.  In  side-hill 
work  the  amount  of  excavation  will  increase  with  increase  in  width 


CANALS. 


591 


beyond  a  certain  point.      Too  deep  a  channel  will  also  be  unsuitable  in 
such  situations.      Fig.  1 50  illustrates  a  section  built  almost  entirely  by 


FIG.  150. — CANAL  SECTION  IN  EMBANKMENT. 

embankment.     The  best  material  is  placed  in  the  center  of  the  embank- 
ments,   and    drainage-ditches    for    surface-water 
are  provided.      Fig.   151  illustrates  suitable  pro- 
portions for  side-hill  work  in  rock. 

The  size  of  cross-section  should  be  large 
enough  to  give  the  required  capacity  when  the 
canal  is  covered  with  ice  to  the  maximum  thick- 
ness. If  the  velocity  is  low,  a  considerable  allow- 
ance should  also  be  made  for  growth  of  weeds 
and  grass. 

618.  Other  Details. — The  construction  of  im- 
pervious banks  follows  the  same  general  principles  as  laid  down  for 
reservoir  construction.  Side  slopes  in  ordinary  soils  will  vary  from 
I  to  I  for  hard  clay  and  gravel,  to  3  to  I  or  4  to  I  for  fine  sand. 
The  tops  of  the  bank  should  be  from  I  to  2  feet  above  the  water-line. 
It  is  well  to  construct  a  berme  just  above  the  water-line,  or  at  the 
original  surface  of  the  ground,  above  which  the  slopes  of  the  bank 
may  frequently  be  made  steeper  than  below.  If  the  soil  is  very  porous, 
a  lining  of  concrete  or  puddle  may  be  necessary.  Some  canals  have 
been  lined  with  a  layer  of  but  2  or  3  inches  of  concrete,  placed  on  the 
earth  and  plastered  with  Portland-cement  mortar.  Fig.  152  illus- 


FIG.    151. — CANAL  SEC- 
TION ON  SIDE  HILL. 


FIG.  152. — SANTA  ANA  LINED  CANAL. 

trates  a  form  of  section  used  on  the  Santa  Ana  Canal,  California.  If 
a  very  heavy  lining  is  required,  it  will  usually  be  better  to  build  a 
covered  masonry  aqueduct,  as  this  avoids  trouble  from  ice  and  protects 
the  water  from  pollution.  The  presence  of  clay  and  silt  in  the  water 
will  tend  gradually  to  reduce  percolation. 


592  ,         CONDUITS  AND    PIPE-LINES. 

At  sharp  bends,  and  wherever  the  velocity  exceeds  the  safe  velocity 
for  the  material,  some  form  of  revetment  is  necessary.  This  may  be 
merely  a  layer  of  gravel,  or  a  paving  laid  dry  or  in  cement,  or  a  layer 
of  concrete,  according  to  the  velocity  of  the  water.  If  the  general 
slope  of  the  ground  is  too  great  for  the  canal,  the  fall  may  be  con- 
centrated at  a  few  points  by  dams,  below  which  the  channel  must  be 
protected  against  scour,  as  described  in  Chapter  XVII.  On  side-hill 
work  a  ditch  should  be  constructed  on  the  upper  side  to  carry  off  sur- 
face drainage.  The  lower  side  of  the  canal  at  such  places  will  often 
consist  of  a  masonry  wall  as  shown  in  Fig.  151. 

Waste-weirs  and  sluice-gates  should  be  provided  at  intervals  along 
the  canal  to  prevent  flooding  and  to  permit  of  rapid  emptying. 
These  wasteways  should  be  located  near  some  natural  watercourse  into 
which  the  waste-water  can  be  conducted  by  suitable  channels.  The 
flow  in  the  canal  is  regulated  for  the  most  part  by  sluice-gates  at  the 
head  of  the  canal.  These  and  other  forms  of  canal  gates  are  sup- 
ported either  by  masonry  walls,  or  by  timber  framework.  Stop-planks 
fitting  into  grooves  in  the  masonry  are  suitable  for  weirs,  and  for  gates 
which  are  but  seldom  operated. 

Canals  are  carried  across  valleys  on  trestles  or  bridges,  or,  in  the 
case  of  short  crossings,  on  embankments  with  a  culvert  or  arched 
bridge  beneath.  Under-crossings  are  made  by  means  of  inverted 
siphons  of  pipe. 

A  recently  excavated  canal  for  water-supply  purposes  is  one  15,800  feet 
long,  carrying  the  water  from  the  new  Wachusett  aqueduct  of  the  Metropolitan 
Water-supply  of  Boston,  down  an  old  waterway  to  one  of  the  old  reservoirs. 
It  is  20  feet  wide  on  the  bottom,  with  side  slopes  3  to  i.  To  avoid  too  high 
a  velocity  two  dams  were  built  giving  two  moderate  falls.  Bermes  at  least 
10  feet  wide  were  constructed  on  each  side,  and  the  slopes  above  were  made 
not  steeper  than  2  to  i.  Where  dug  through  fine  sand  the  canal  was  faced 
with  gravel  or  riprap.  * 

619.  Flumes. — Where  excavation  for  a  canal  is  difficult,  flumes  of 
wood  are  often  used  for  temporary  works  and  for  irrigation  purposes 
on  account  of  their  low  first  cost.  They  are  usually  constructed  with 
horizontal  bottoms  and  vertical  sides,  but  a  more  advantageous  form,  in 
which  wooden  staves  are  used  for  the  lower  portion,  has  recently  been 
employed  on  the  Santa  Ana  Canal  in  California,  t  A  flume  can  be 
made  much  smaller  than  a  canal  on  account  of  the  high  velocity  of  6 

*  Report  Mass.  Board  of  Health,  1895^  on  the  Metropolitan  Water-supply. 
\  See  Trans.  Am.  Soc.  C.  E.,  1895,  xxxm.  p.  61. 


MASONRY  AQUEDUCTS.  593 

or  8  feet  per  second  permissible.      There  is  also  much  less  resistance 
to  flow,  thus  giving  much  less  loss  of  head  for  like  capacity. 


MASONRY    AQUEDUCTS. 

620.  Advantages  of  Masonry  Aqueducts. — For  conveying  relatively 
large  quantities  of  water  over  territory  where  the  conduit  can  readily 
follow  the  hydraulic  grade-line,  the  masonry  conduit  in  cut  and  cover 
is  a  preferable  form  of  construction.      If  properly  constructed  it  is  very 
durable,  requires  little  attention,  and  if  the  topography  is  favorable  it 
is  much  cheaper  than  large  pipe  conduits  of  iron  or  steel.      Masonry 
is  unsuited  to  withstand  tensile  stresses,  hence  it  is  not  used  to  convey 
water    under    pressure.       Combinations   of  steel   and    concrete    may, 
however,   be   used   for    this    purpose.       Masonry  conduits  would    not 
often  be  employed  for  cross-sections  less  than  10  or  15  square  feet,  for, 
unless  the  location  be  very  favorable,  their  cost  for  such  small  sizes 
is  likely  to  be  greater  than  that  of  steel  or  iron  pipes. 

621.  Size  of  Cross-section,  Velocity,  and  Slope. — The  size   of  cross- 
section,  the  velocity,  and  the  slope  are  interdependent,  one  of  the  last 
two   elements   being   usually   the   determining    factor.      The    velocity 
should  preferably  be   such   as  to  prevent  deposit  of  sediment,  which 
requires  2\  to  3  feet  per  second  average  rate ;  and  for  brick  or  concrete 
masonry  it  should  not  exceed  6  or  7  feet  per  second.      Higher  veloc- 
ities may  be  allowed  if  stone  masonry  of  hard  material  is  employed,  or 
if  a  lining  of  iron  or  steel  is  used.      The  question  is  usually  determined 
by  the  available  head  between  the  terminal  points  of  the  conduit,  or  by 
the  topography  of  the  locality.     If  sufficient  head  is  available,  a  smaller 
conduit  will  result  if  the  velocity  is  made  as  large  as  the  material  will 
stand  without  danger  of  excessive  wear. 

The  circular  form  of  cross-section  gives  the  greatest  hydraulic 
mean  radius  and  therefore  the  minimum  area  of  section,  but  this  form 
is  not  the  most  economical  in  construction.  For  large  aqueducts  the 
form  which  experience  has  shown  to  be  the  best  is  that  illustrated  in 
Figs.  157  and  158.  The  hydraulic  radius  of  this  section  is  but  little 
less  than  that  of  a  circular  section. 

Whatever  the  section  adopted,  the  values  of  the'  hydraulic  radius, 
velocity,  and  discharge  for  different  depths  of  water  should  be  tabu- 
lated for  convenient  use  in  computations.  It  will  usually  be  the  case 
that  a  conduit  will  flow  only  part  full  for  the  first  few  years,  and  the 
design  should  be  made  with  reference  to  the  fact  that  as  the  flow 
increases  the  velocity  will  increase.  Kutter's  formula  is  usually  em- 


594 


CONDUITS  AND  PIPE-LINES. 


ployed  in  calculations.  The  value  of  n  to  be  used  will  vary  with  the 
character  of  the  masonry  about  as  given  on  page  256.  The  resistance 
to  flow  may  be  very  greatly  increased  in  a  few  years  after  the  conduit 
has  been  put  into  use,  by  the  formation  of  deposits  or  by  organic 
growths.  The  capacity  of  the  New  Croton  Aqueduct  has  diminished 
from  such  causes  about  14  per  cent  in  9^  years. 

622.  Materials  Employed.  —  Up  to  about    1895   brick  and  rubble 
masonry  were  the  materials  generally  employed  for  aqueduct  construc- 
tion, the  lining  and,  frequently,  the  arch-crown  being  of  brick.     Concrete 
was  first  used  in  place  of  the  rubble  in  foundations  and  side  walls,  brick 
being  still  used  for  the  arch,  or  as  a  mere  lining,  as  in  the  Massachusetts 
aqueduct  illustrated  in  Fig.  158.     In  still  later  work  concrete  has  almost 
entirely  superseded  other  material,   the   brick   lining   being    generally 
replaced  by  a  lining  of  cement  mortar,  or  no  special  lining  at  all  being 
used.     Reinforced  concrete  may  be  used  to  advantage  in  some  cases, 
especially  where  the  foundation  is  soft  and  where  special  forms  of  cross- 
section  are  required.     In  compact  ground  the  advantage  of  reinforced 
concrete  is,  however,  doubtful,  as  not  much  material  can  be  saved  by 
its  use  over  that  required  in  a  properly  proportioned  plain  concrete 
structure.     The  general  change  which  has  taken  place  in  the  past  1 5  or 
20  years  is  well  illustrated  by  the  designs  represented  in  Figs.  I57~i59a. 
In  the  use  of  concrete,  Portland  cement  has  almost  entirely  replaced 
natural  cement  for  all  purposes.* 

623.  Form  and  Stability  of  Section.  —  The  forces  to  be  considered  in 
designing  a  section  are  the  pressure  of  the  water,  the  earth-pressure, 


FIG.  153. 
GALLERY,  VIENNA  WATER-WORKS. 


FIG.  154. 
SMALL  FRENCH  AQUEDUCT. 


and  the  weight  of  the  masonry.  Besides  being  of  sufficient  strength 
the  section  must  be  of  convenient  form  for  construction  and  inspection, 
and  it  must  be  economical.  For  small  aqueducts  a  rectangular  form 

*  See  also  Art.  759. 


MASONRY  AQUEDUCTS. 


595 


has  often  been  used,  as  in  Figs.  153  and  154,  the  cover  being  of 
stone  slabs  or  of  arches.  The  Manchester  aqueduct  is  also  of  this 
general  form  (Fig.  155).  Sharp  angles  are,  however,  objectionable, 
and  these  can  be  avoided  and  an  increased  capacity  obtained  at  little 
cost  by  building  the  bottom  as  an  inverted  arch.  Such  a  form  is  also 
better  suited  to  resist  any  upward  pressures.  If  there  is  lateral  earth 
pressure,  the  sides  will  also  be  strengthened  by  curving  them.  These 


In  RocK  •  JnComjxjct 'Earth-     *  -    ; 

FIG.  155.  FIG.  156. 

MANCHESTER  AQUEDUCT.         DHUIS  AQUEDUCT,  PARIS  WATER-WORKS. 

modifications  give  rise  to  the  horseshoe  shape  as  commonly  used  for  large 
'conduits.  To  make  the  bottom  of  short  radius,  giving  a  circular  or 
elliptical  section,  is  not  so  convenient  in  practical  construction,  although 
to  give  head-room  in  small  conduits  the  elliptical  or  oval  section  has 
been  used  (Fig.  156). 

In  the  case  of  small  conduits  built  in  compact  earth,  the  water-pres- 
sure and  the  arch-thrust  may  be  considered  as  largely  resisted  by  the 
earth,  but  to  insure  this  the  back-filling  up  to  the  springing-line  should 
be  entirely  of  concrete  (Figs.  155  and  158).  In  rock,  a  lining  of  one 
or  two  rings  of  brick,  or  of  brick  and  concrete,  is  all  that  is  necessary. 
In  loose  earth,  and  especially  on  embankments,  the  side  walls  should  be 
heavy  and  have  broad  foundations.  Little  dependence  can  be  placed 
upon  the  lateral  thrust  of  the  earth  in  an  embankment,  and  experience 
indicates  that  in  the  settling  of  embankments  there  is  a  tendency  for 
the  walls  to  spread,  and  large  longitudinal  openings  or  cracks  have  been 
formed  in  aqueducts  in  this  way.  Inverts  of  reinforced  concrete  are 
very  effective  under  such  conditions.  Several  sections  of  modern 
aqueducts  are  shown  in  Figs.  i5/-i59a.  Fig.  iSQa  illustrates  a  rein- 
forced concrete  design.  Where  not  reinforced  the  arch  ring  must  be 
of  sufficient  thickness  to  avoid  tensile  stresses.  By  carefully  pro- 
portioning the  side  walls  and  arch  with  reference  to  the  pressures 
acting,  a  comparatively  small  thickness  of  crown  will  be  sufficient.  In 


596  CONDUITS  AND  PIPE-LINES. 

MBVOmBM 


FIG.  157.  —  SECTIONS  OF  THE  NEW  CROTON  AQUEDUCT,  (1885). 


In  Loose  Earth       )n  Compact  Earth 


In  .RocK 


Timber    foundation   and   Drain. 

FIG.  158.  —  SECTIONS  OF  THE  WACHUSETT  AQUEDUCT,  BOSTON,  (1895, 


Stee/Pocfs* 

Under  High  Embankment     j  Dry  Earth  Section  Section  in  Rock 

FIG.  159.  —  SECTIONS  OF  THE  CATSKILL  AQUEDUCT,  (1906). 


MASONRY  AQUEDUCTS 


597 


Pemforcing  Pods 


Section  in  Soft  Earth 
Bottom 


Section  on  Foundation 
Cmbankmenr 


this  respect  the  later  designs  are  notably  more  economical  than  the 
earlier  ones.  (Compare  Figs.  159  with  157  and  158.)  If  reinforced 
concrete  is  used  a  somewhat  lighter  section  may  be  employed,  especially 
near  the  base  of  the  side  walls. 

The  invert,  in  compact  ground,  is  made  only  thick  enough  to  secure 
a  firm,  impervious  bottom.  Even  where  the  excavation  is  made  through 
impervious  rock,  an  invert  of 
brick  or  concrete  is  desirable 
as  giving  a  smoother  bottom 
for  cleaning  and  inspection 
and  one  offering  less  resist- 
ance to  flow.  In  soft  foun- 
dations, or  on  embankments, 
the  invert  should  be  made 
thick  and  strong,  preferably 
of  reinforced  concrete,  in 
order  to  be  able  to  act  as  a 
beam  and  so  aid  in  distributing  FIG.  1 59a.  —  JERSEY  CITY  CONDUIT. 

the  weight  of  the  side  walls. 

(See  Fig.  159.)  Timber  or  pile  foundations  may  be  required  on  soft 
soils.  Settlement  must  be  reduced  to  very  low  limits  or  cracks  and 
leakage  will  result. 

624.  Constructive  Features.  —  It  is  unnecessary  to  state  that  in  work 
of  this  kind  the  masonry  must  be  constructed  with  the  most  careful 
supervision.  In  wet  soils,  drains  should  be  built  beneath  the  invert  to 
enable  the  masonry  to  be  laid  without  trouble  from  water.  The  drains 
may  be  led  into  the  conduit  at  a  point  lower  down  and  the  water  per- 
mitted to  flow  through  the  completed  portion.  Concrete  and  stone 
masonry  should  be  given  one  or  two  finishing  coats  of  thin,  neat  cement 
to  secure  imperviousness,  the  last  coat  to  be  finished  as  smooth  as 
practicable.  If  carefully  done,  and  no  settlement  occurs,  the  leakage 
will  be  slight.  Successive  sections  of  concrete  construction  should  be 
connected  by  deep  key  joints  and  in  order  to  permit  some  contraction 
without  leakage,  it  is  desirable  to  insert  tongues  of  lead  or  plate  iron 
every  50  or  75  feet. 

Where  built  on  embankment  the  greatest  care  must  be  used  in 
constructing  the  earthwork  in  order  to  avoid  settlement.  The  follow- 
ing is  an  extract  from  the  specifications  for  the  Wachusett  aqueduct 
relating  to  embankment  construction  : 

"  The  central  portion  of  the  bank,  beneath  the  level  of  the  highest  part 
of  the  base  of  the  aqueduct,  to  a  width  8  feet  greater  than  that  of  the  base 


598  CONDUITS  AND   PIPE-LINES. 

at  such  level,  and  to  an  added  width  of  i  foot  for  each  foot  below  such  level, 
is  to  be  built  with  extreme  care  and  with  carefully  selected  earth;  all  stones 
larger  than  2  inches  in  diameter  are  to  be  thrown  out.  The  material  is  to  be 
deposited  and  spread  in  horizontal  layers  not  exceeding  3  inches  in  thickness, 
each  layer  to  be  sufficiently  watered  and  very  thoroughly  rolled  with  a  heavy 
grooved  roller.  From  time  to  time  during  the  construction  of  this  portion  of 
the  embankment,  and,  if  so  required,  three  times  after  its  completion,  this 
portion  shall  be  so  thoroughly  saturated  with  water  that  it  will  stand  upon 
the  surface.  The  building  of  the  aqueduct  upon  such  embankments  shall 
not  be  begun  until  they  have  stood  six  weeks  after  completion,  unless  other- 
wise directed/' 

The  requirements  for  the  remainder  of  the  earthwork  were  some- 
what less  severe.  The  embankments  have  in  general  a  top  width  of 
14  feet,  with  side  slopes  of  if  to  I .  They  start  from  a  base  from  which 
all  soil  and  all  other  perishable  matter  are  removed,  and  on  sloping- 
ground  the  base  is  stepped.  If  founded  on  soft  material,  such  material 
must  be  removed  or  piles  be  used.  Experience  proves  that  with  good 
material  and  careful  work  the  settlement  of  embankments  will  be  very 
slight. 

Trenches  should  not  be  back-filled  until  the  cement  has  had  time 
to  harden  considerably,  and  then  it  should  be  carefully  done  from 
both  sides  simultaneously.  The  evils  of  too  hasty  loading  of  the  arch 
have  been  well  shown  by  Mr.  A.  Fteley,  by  means  of  a  device  for  meas- 
uring the  deformations  of  the  cross-section.  The  use  of  this  during  the 
progress  of  the  construction  of  a  large  aqueduct  showed  a  considerable 
settlement  of  the  crown,  due  to  too  early  loading.  The  diagrams  also 
showed  the  insufficient  strength  of  invert  in  yielding  ground.* 

The  aqueduct  should  be  covered  to  a  depth  of  3  or  4  feet  to  prevent 
the  formation  of  ice  and  to  protect  the  masonry.  Embankments 
should  be  given  a  slope  of  i^  to  2  horizontal  to  I  vertical,  according 
to  the  nature  of  the  material.  They  should  be  trimmed  to  a  rounded 
outline  and  then  sodded. 

625.  Special  Details. — Masonry  aqueducts,  like  canals,  should  be 
provided  with  gates,  wasteways,  and  overflow-weirs  at  intervals,  to 
maintain  the  water-level,  and  to  enable  the  aqueduct  to  be  emptied  in 
parts.  Masonry  aqueducts  are  not  designed  to  flow  under  pressure, 
and  to  insure  safety  in  this  respect,  long  aqueducts  will  require  the 
construction  of  waste-weirs.  Gates  should  be  constructed  at  the  junc- 
tion of  aqueduct  with  pipe-lines  or  siphons,  and  at  terminal  points. 
Intermediate  wasteways  or  blow-offs  are  located  near  some  natural 
watercourse,  and  should  have  a  capacity,  if  possible,  equal  to  that  of 
the  aqueduct.  Fig.  160  shows  one  of  the  wasteways  of  the  New  Croton 

*  Jour.  Assn.  Eng.  Soc.,  1883,  n.  p.  123. 


MASONKY  AQUEDUCTS. 


599 


Aqueduct  and  a  stream-crossing  at  the  same  place,  and  Fig.  161  illus- 
trates an  undercrossing  of  the  Brooklyn  conduit.* 


440- 


Section  AB 
FIG.  160. — BLOW-OFF  AND  CULVERT,  NEW  CROTON  AQUEDUCT. 


FIG.  161. — UNDERCROSSING,  BROOKLYN  CONDUIT. 

Culverts  for  crossing  small  streams,  and  bridges  for  larger  ones,  are 
a  part  of  the  design.  Some  of  the  most  monumental  works  of  history  are 
the  bridges  which  have  been  built  for  carrying  aqueducts.  Large  aque- 
duct bridges  are  now  seldom  constructed,  pipe-lines  being  substituted, 
but  bridges  of  moderate  size  will  still  often  be  the  more  economical 
design.  These  are  usually  masonry  structures,  and,  as  in  the  case  of 

*  Eng.  News,  1891,  XXV.  p.  225. 


600  CONDUITS  AND   PIPE-LINES. 

embankments,  special  pracautions  must  be  taken  to  prevent  settlement. 
Experience  with  other  structures  of  a  similar  character  led  the  engineers 
of  the  Wachusett  aqueduct  to  adopt  certain  special  precautions  in  the 
construction  of  the  Assabet  bridge.  This  is  a  masonry  structure  3#£ 
feet  long  and  of  seven  spans.  The  brick  lining  of  the  aqueduct  was 
first  covered  with  a  coat  of  cement  mortar,  which  was  then  painted. 
Sheets  of  lead  weighing  5  pounds  per  square  foot  were  then  carefully 
cemented  in  place,  coated  with  asphalt,  and  the  interior  lined  with 
8  inches  of  brick.  The  roof  is  of  brick  arches  on  I  beams,  and  is 
covered  with  cement  and  asphalt. 

Small  streams  are  led  under  aqueducts  through  culverts,  or  through 
inverted  siphon-pipes  with  gratings  at  entrance. 

626.  Tunnels. — Tunnels  frequently  form  a  part  of  an  aqueduct. 
The  section  adopted  is  usually  the  same  as  for  the  masonry  portion, 
but  the  circular  form  may  here  be  used.  In  unstable  material  a  brick 
lining  will  be  required.  If  a  tunnel  is  unlined,  the  section  should  be 
increased  by  15  to  20  per  cent  to  allow  for  increased  resistance  due  to 
the  roughness  of  the  surface.  The  unlined  portion  'of  the  Wachusett 
tunnel  is  thus  made  about  21  per  cent  larger  than  the  lined  portion; 
likewise  in  the  case  of  the  Manchester  aqueduct  the  increase  in  section 
is  about  1 6  per  cent.  Mr.  J.  R.  Freeman  adopts  for  certain  proposed 
aqueducts  for  New  York  City  a  value  of  n  in  Kutter's  formula  of  .028 
for  unlined  tunnel  and  .014  for  lined  tunnel.  He  estimates  that  for 
large  sizes  the  lined  tunnel  is  actually  cheaper  for  a  given  capacity 
than  the  unlined.* 

Tunnels  are  usually  built  to  flow  free,  but  sometimes  are  operated 
under  pressure.  Thus  the  Croton  aqueduct  tunnel  is  under  about  125 
feet  pressure  for  7  miles,  and  under  the  Harlem  River  the  head  is 
about  425  feet,  the  hydraulic  grade-line  being  there  120  feet  above  the 
river.  The  actual  unbalanced  water-pressure  on  the  aqueduct  lining 
would  be  the  difference  between  the  inside  pressure  and  the  pressure 
of  the  ground-water,  which,  at  the  river-crossing,  would  probably  be 
measured  by  the  level  of  the  water  in  the  river.  If  the  ground-water 
pressure  is  in  excess,  there  would  be  filtration  into  the  tunnel. 

It  appears  to  be  difficult  to  secure  good  work  in  placing  the  back- 
ing of  tunnels,  and  the  defects  in  this  respect  are  notorious  in  one  or 
two  large  aqueducts.  Recent  experiments  by  Col.  A.  M.  Miller,  U.  S. 
Engineer,  have  shown  that  cavities  which  are  not  easily  filled  with 
masonry  in  cement,  can  be  filled  dry  and  successfully  cemented  by 
forcing  in  grout  under  pressure. t 
*  Report  on  New  York's  Water-supply,  1900,  p.  318.  f  Eng.  News,  1899,  XLII.  p.  410. 


DESIGN  OF  PIPE-LINES.  6OI 

627.  Aqueducts  of  Vitrified  Pipe.  —  As  already  described  in  the  last 
chapter  (page  581),  vitrified  pipe  can  well  be  used  for  small  aqueducts 
not  under  pressure.  This  pipe  is  considerably  smoother  than  brick 
masonry,  and  for  any  given  capacity  will  be  more  economical,  at  least 
for  sizes  up  to  24  to  30  inches,  and  possibly  for  the  36-inch  size. 


PIPE-LINES. 


The  General  Design. 


628.  Material  to  be  Employed.  ^The  advantages  of  various  materials 
have  been  considered  in  the  last  chapter.     Summarizing  briefly,  it  may 
be  said  that  cast  iron  is  especially  suited  for  conduits  of  small  or  moder- 
ate size,  and  for  places  where  frequent  use  of  branches  and  specials  is 
called   for.      Steel   is   especially   suited   for   very   large   sizes,  and   for 
heavy  pressures,  and  for  lines  in  those  situations  where  a  light  pipe  is 
especially  desirable.    Wooden  pipe  is  adapted  for  use  in  remote  regions, 
for  low  pressures,  and  where  the  pipe  is  to  be  exposed.     Vitrified  pipe 
may  be  used  for  small  sizes  and  very  low  pressures. 

629.  The    Profile  —  The   question    of    location    has    already  been 
touched  upon  in  a  general  way  in  Art.  614.      A  pipe-line  must  follow 
in  general  the   variations   of  the  ground-surface,  and   such   a  location 
should  be  selected   as  will   enable  it  to  do  so  and  at  the  same  time 
give  low  pressures,   that  is,  it  should  be  kept  as  near  the  hydraulic 
grade-line  as  possible.    If  the  pipe  is  made  of  uniform  size,  the  hydrau- 
lic grade-line  will  be  a  straight  line  from  one  end  to  the  other;  but  if 
it  is  not  practicable  to  keep  the  pipe-line  below  a  continuous  grade- 
line  at  all  points,  an  intermediate  reservoir  may  be  placed  at  the  high 
point  and  the  sections  on  either  side  designed  independently.      Several 
such  breaks  may  evidently  be  advisable  in  some  cases.      If  the  inter- 
mediate points  are  too  high  for  this  arrangement,  then  a  deep  cut  or 
a  tunnel  will  probably  be  desirable.      Small  elevations  above  the  hy- 
draulic gradient  may  be  overcome  by  siphonage,  but  this  will  require 
special  provision  for  the  removal  of  air.      In  other  cases  pumping  may 
be  resorted  to. 

If  the  pipe-line  dips  too  far  below  a  straight  grade-line,  it  may  save 
expense  to  break  the  grade  in  this  case  also,  by  means  of  an  interme- 
diate reservoir  so  located  as  to  give  sufficient  fall  in  the  lower  part  of 
the  conduit.  Thus,  in  Fig.  162,  AB  is  the  grade-line  with  a  pipe  of 
uniform  size,  and  ACB  the  gradient  when  a  reservoir  is  inserted  at  C. 
The  latter  arrangement  gives  much  the  lower  pressures. 


602  CONDUITS  AND   PIPE-LINES. 

Overflows  and  equalizing  reservoirs  are  advantageous  for  regulating 
the  pressure  in  the  pipe ;  and  to  permit  of  their  economical  construction 
it  is  desirable  to  have  the  pipe-line  approach  or  cut  the  hydraulic  grade- 
line  occasionally.  Plan  and  profile  should  be  so  laid  out  as  to  avoid 
sharp  curves  as  much  as  possible,  and  the  curves  used  should  conform 
to  certain  adopted  standards.  In  deep  valleys  and  gorges  it  will  often 


FIG.  162. 

be  best  to  carry  the  pipe  for  a  short  distance  on  a  trestle  or  bridge, 
thus  avoiding  sharp  curves  and  at  the  same  time  shortening  the  line. 

630.  Pressures  to  be  Assumed. — The  water-pressures  in  a  pipe-line 
are  measured  by  the  ordinates  to  the  hydraulic  grade-line,  which  has 
a  slope  depending  upon  the  frictional  loss.  When  the  water  is  station- 
ary the  hydraulic  grade-line  is  horizontal  and  the  pressures  will  be  the 
same  at  all  points  at  the  same  level.  When  flowing,  the  pressures  will 
be  much  reduced  at  certain  points.  If  a  pipe-line  is  so  designed  that 
the  lower  end  is  closed  at  times,  the  pressures  must  be  assumed  to  be 
static,  i.e.,  measured  from  a  horizontal  hydraulic  grade-line;  but  if  it 
is  so  arranged  that  the  water  will  always  have  free  egress,  then  the 
pressures  will  be  measured  from  the  sloping  hydraulic  grade-line,  and 
much  will  be  saved  in  cost  of  pipe.  In  practice,  the  second  condition 
is  often  practically  obtained  by  placing  small  reservoirs  and  overflows 
on  the  hydraulic  grade-line  at  intervals  where  the  pipe-line  rises  close 
to  this  elevation.  Each  section  of  pipe  between  consecutive  reservoirs 
may  then  be  operated  in  the  ordinary  way  and  designed  for  the  static 
pressure.  This  gives  a  pressure-line  consisting  of  a  series  of  horizontal 
lines.  The  method  of  designing  for  a  sloping  hydraulic  grade-line 
requires  that  no  part  of  the  line  can  possibly  be  closed  except  at  the 
extreme  upper  end.  In  this  case  also  it  is  well  to  have  overflows  at 
various  points  along  the  pipe-line.  Obviously  both  methods  of  design- 
ing may  be  employed  for  different  sections  of  a  conduit. 

An  example  of  a  combination  of  both  methods  is  the  Rochester 
conduit,  the  profile  of  which  is  shown  in  Fig.  163.  The  pipe  is  a 
38-inch  steel  pipe  26£  miles  long.  In  the  middle  of  a  i/^mile  sec- 
tion an  overflow-tower  is  connected  to  the  pipe,  and  is  always  kept 


DESIGN  OF  PIPE-LINES.  603 

open,  thus  limiting  the  pressures  on  the  upper  half  to  those  due  to 
the  hydraulic  grade-line.  A  waste-pipe  leads  to  a  near-by  creek. 
The  lower  half  is  designed  for  static  pressure  and  is  provided  with 
gates  in  the  usual  manner. 

In   the   case  of  large    pipe-lines   not   connected  with   distributing 
systems  the  pressure  to  be  considered  in  the  design  need  not  be  much 


O  2O.OOO 

FIG.  163. — PROFILE  OF  ROCHESTER  PIPE-LINE. 

increased  for  the  item  of  water-hammer.      This  is  especially  true   of 
pipes  ending  in  reservoirs  and  operated  with  open  ends. 

631.  Calculation  of  Size  of  Pipe — Where  the  total  available  head  is 
fixed,  the  size  required  for  any  given  capacity  is  readily  determined. 
If  the  head  is  very  small,  the  size  required  will  be  relatively  large,  and 
it  may  be  more  economical  to  use  pumps,  with  a  smaller  pipe-line,  de- 
signed  as  explained  below.      In  case   the   water   contains  suspended 
matter,  it  is  desirable  to  maintain  a  self-cleansing  velocity  of  2  to  2^  feet 
per  second,  otherwise  the  sediment  must  be  blown  out  at  frequent  inter- 
vals.    If  the  line  is  divided  into  sections  by  reservoirs  or  overflows,  the 
size  of  each  section  is  determined  independently  of  the  others. 

632.  Economical  Size  of  Pipes  where  Pumping  is  Required, — If  the 
loss  of  head  is  not  fixed,  as  is  the  case  where  the  pressure  is  supplied 
by  pumps,  the  size  of  pipe  should  be  such  as  to  make  the  total  yearly 
expense  a  minimum.     If  the  cost  of  various  sizes  of  pipe  is  known,  and 
the  cost  of  pumping  per  unit  of  work  done,  the  problem  can  readily  be 
solved  by  a  few  trials. 

In  most  cases  the  possible  variation  in  pipe  would  not  seriously 
affect  the  design  of  the  pumps,  and  the  cost  of  fuel  would  be  about  the 
only  item  affected  by  a  small  change  in  head.  The  additional  cost 
would  then  be  small.  In  the  case  of  very  long  force-mains,  however, 
or  pipe-lines  with  several  pumping-stations,  nearly  all  items  of  expense 
would  be  affected  by  a  change  in  size  of  pipe. 


604  CONDUITS  AND    PIPE-LINES. 

As  this  problem  is  of  common  occurrence  in  connection  with  dis- 
tributing systems  as  well  as  pipe-lines,  an  approximate  general  solution 
for  cast-iron  pipe  will  be  given,  from  which  a  good  notion  of  the 
economical  velocities  for  various  sizes  of  pipes  can  be  had. 

From  an  analysis  of  Weston's  tables  and  other  data  relating  to  the 
cost  of  cast-iron  pipe,  it  is  found  that  the  cost  of  pipe,  laid,  is  approxi- 
mately given  by  the  formula 


(i) 


in  which  c  =  cost  per  foot  in  cents, 

a  =  cost  of  iron  in  cents  per  pound, 
and  d  =  diameter  of  pipe  in  inches. 

If  in  eq.  (31),  page  230,  we  express  dm  inches  instead  of  feet,  we 
have,  for  the  velocity  of  flow  in  pipes, 


(2) 


in  which  v  =  velocity  in  feet  per  second,  and 
s  =  slope  of  hydraulic  grade  line, 

=  loss  of  head  in  feet  per  foot. 
From  eq.  (2)  we  get 


j.      .......     (3) 

We  also  have  the  general  relation 

e  =  "•!*(,!)'•  ........  (4) 

Then  from  eqs.  (3)  and  (4)  we  have 

& 


= 


(5) 


Let  b  =  yearly  cost  of  pumping  i  cubic  foot  per  second  i  foot  high, 
and  Q  =  volume  pumped  per  second.  Furthermore,  let  r  =  rate  of 
interest  plus  rate  of  depreciation  of  pipe-line.  The  total  yearly  cost 
of  pipe  and  pumping,  per  foot  of  pipe,  will  then  be 

A  =  bsQ  +cr=  bsQ  +  2or  +  2ard*-&.       ...     (6) 


DESIGN  OF  PIPE-LINES.  605 

Substituting  the  value  of  s  from  eq.  (5),  we  have 


A  =  ioo^5  +  20r  +  2ard^  .....      (7) 


Differentiating  with    respect  to  d,    etc.,   we  find  that  for  a  minimum 
value  of  A 


that  is,   for  any  given  values  of  b    and   a  the  diameter  should  vary 
with  Q*. 

To  express  this  relation  in  terms  of  velocity,  which  is  a  more  con- 
venient form,  we  may  substitute  from  (4);  whence  we  have  ,  for  the 
economical  velocity, 

*  1 

-v  .......    ..      (9) 

The  cost  of  pumping  is  ordinarily  expressed  in  terms  of  cost  per 
1,000,000  gallons  lifted  I  foot  high.  This  will  vary  largely  in  different 
plants,  but  the  cost  of  additional  lift  will  seldom  exceed  3  to  4  cents 
per  million-gallon  foot,  and  in  large  plants  will  not  exceed  2  cents. 
The  total  cost  of  pumping  in  large  plants  is  usually  from  3  to  5  cents. 

Table  No.  77  gives  various  values  of  v  as  computed  from  eq.  (9) 
for  various  costs  of  pumping.  The  cost  of  pipe  is  taken  at  I  cent  per 
pound,  interest-rate  4  per  cent,  and  a  depreciation  of  pipe-line  of  I  per 
cent  per  year.  For  other  values  of  the  cost  of  pipe,  (a),  or  of  interest 
plus  depreciation,  (r),  multiply  the  value  of  v  given  in  the  table  by  a^ 


u 
or  by    - 


* 


If  the  pumping  is  done  at  a  variable  rate,  then  the  maximum 
velocity  should  be  made  somewhat  greater  than  the  value  given  in  the 
table.  If,  for  example,  the  pumps  are  operated  for  half  the  time  at  a 
rate  <2>  then  the  value  of  b  will  be  equal  to  the  total  yearly  cost  divided 

Q 
by  the  rate  Q  and  by  the  head,  and  will  hence  be  less  than  if  a  rate  — 

were  maintained  for  the  entire  year  at  nearly  the  same  total  cost. 
The  resulting  value  of  v  will  therefore  be  greater  ;  in  the  assumed  case 
it  will  be  equal  to  the  value  given  by  the  table  multiplied  by  2s6  or  by 

I-3- 

For  other  than  cast-iron  pipe  the  actual  cost  will  be  different  from 
the  cost  here  assumed,  but  the  variation  in  cost  of  pipe  with  size  will 


6o6 


CONDUITS  AND   PIPE-LINES. 


be  proportionately  about  the  same,  so  that  an  approximate  value  for 
velocity  can  be  found  by  using  the  table  with  such  a  cost  of  cast  iron 
as  will  give  the  correct  cost  of  some  one  size  of  conduit.  As  in  all 
cases  of  maximum  and  minimum,  a  considerable  change  in  the  value 
of  the  variable  when  near  to  the  correct  value  will  affect  the  result  but 
slightly.  Another  factor  which  usually  enters  is  the  gradual  increase  in 
the  quantity  of  water  which  is  to  be  pumped,  so  that  the  pipe  must  at 
first  be  made  too  large  for  economy. 

TABLE    NO.    77. 

ECONOMIC  VELOCITIES  IN  CAST-IRON  MAINS  WHEN  THE  COST  OF  PIPE  IS  I  CENT  PER 
POUND,  AND  THE  COST  OF  ADDITIONAL  LIFT  IS  2,  4,  AND  6  CENTS  PER  MILLION- 
GALLON-FOOT.  INTEREST  RATE  PLUS  DEPRECIATION  =  5  PER  CENT. 


Cost  of  Pumping 
1,000,000  gal. 
i  foot  high. 

Size  of  Pipe. 

4-in. 

6-in. 

8-in. 

i2-in. 

i6-in. 

24-in. 

3o-in. 

36-in. 

48-10. 

6o-in. 

Velocity  in  Feet  per  Second. 

I.6l 
1-25 
I.OS 

1.82 
I.4I 
1.22 

1-95 
1.52 
I-3I 

2.  IQ 
1.70 
1.47 

2-37 
1.85 
I.  00 

2.65 
2.07 

I.78 

2.82 
2.20 
I.QO 

2.98 
2.32 
2.00 

3-23 
2-51 
2.17 

3-43 
2.67 

2.31 

4  cents 

6  cents              . 

If  pipe  costs  i^  cents,  multiply  above  values  by  1.08. 

"     "        "      4      «'  "  "  ••         "    1.15. 

If  the  pressures  in  a  pipe-line  vary  greatly,  the  most  economical 
size  will  not  be  the  same  for  all  sections,  but  will  vary  a  little,  being 
the  smallest  under  the  heaviest  pressures. 

Construction. 

633*  Plan  and  Profile. — In  preparing  a  design,  an  accurate  map  and 
profile  should  be  made  to  a  large  scale,  on  which  should  be  shown  the 
exact  location  of  the  pipe,  the  radius  and  length  of  each  curve,  location 
and  amount  of  angles  or  bevels,  and  the  position  and  size  of  valves  and 
other  appurtenances.  The  various  sections  of  pipe  and  the  special 
forms  can  then  be  numbered  to  correspond  with  the  location  on  the 
map  so  that  they  can  be  readily  sent  to  their  proper  places. 

634*  Trenching — Trenches  for  water-pipe  are  not  usually  deep 
enough  to  require  much  bracing  or  sheeting,  the  depth  being  ordinarily 
only  sufficient  to  give  the  necessary  covering.  Deep  trenches  will, 
however,  be  required  occasionally,  as  where  the  pipe-line  crosses  a  high 
ridge  extending  above  the  hydraulic  gradient.  The  methods  of 


CONSTRUCTION  OF  PIPE-LINES.  6o/ 

sheeting  and  bracing,  and  of  trenching,  are  the  same  as  used  for  sewer 
work,  and  will  be  found  fully  described  in  works  on  sewerage.  In  wet 
ground,  only  a  short  section  of  trench  should  be  opened  at  once,  in  order 
to  keep  the  inflow  of  water  as  low  as  may  be.  In  rock,  the  trench  must 
be  carried  3  to  6  inches  below  the  proper  grade  and  the  space  refilled 
with  sand  or  fine  material  to  give  a  proper  bedding  for  the  pipe.  Bell- 
holes  for  cast-iron  pipe  must  be  excavated  wide  enough  to  give  plenty 
of  room  for  making  a  good  joint.  All  existing  pipe-lines  and  other 
structures  must  be  carefully  supported  or  removed. 

635.  Foundations. — Where  the  material  is  too  soft  to  give  a  good 
bearing,  it  may  be  necessary  to  use  artificial  foundations.  These  may 
consist  of  blocks  placed  on  stringers,  or  of  piling,  with  caps  on  which 
the  pipe  may  rest.  When  full  of  water  the  pipe  will  weigh  but  little, 
if  any,  more  than  the  soil  displaced,  so  that  there  is  little  tendency 
for  it  to  settle  after  the  back-filling  has  become  compact.  A  foundation 
is  necessary,  however,  to  keep  the  pipe  in  place  during  construction 
and  to  hold  it  rigid  against  unequal  pressures.  For  large  valves  and 
other  heavy  parts,  special  foundations  of  concrete  are  likely  to  be 
needed.  To  assist  in  getting  large  pipe  to  grade,  it  is  convenient  to 
support  it  on  wooden  blocking  and  \vedges,  two  blocks  being  used 
under  each  section.  After  laying,  the  trench  should  be  well  filled 
underneath  the  pipe  by  suitable  material.  At  sharp  curves  and  angles, 
buttresses  of  concrete  or  stone  masonry  should  be  built  to  prevent  dis- 
tortion of  the  line  by  the  water-pressure.  Anchorage  masonry  is  also 
desirable  at  intervals  in  case  the  grade  is  very  steep. 
«  636.  Laying  of  Pipe, — Cast-iron  Pipe. — The  laying  of  cast-iron 
pipe  is  usually  begun  at  a  valve  or  special.  Small  pipe  up  to  6  or  8 
inches  in  diameter  is  easily  handled  without  a  derrick,  the  sections  being 
lowered  into  the  trench  by  two  or  three  men.  In  laying,  care  should 
be  taken  to  enter  the  pipe  to  its  full  depth  and  to  see  that  there  is 
sufficient  joint-space  all  around.  The  pipe  should  have  been  inspected 
for  eccentricity,  and  the  joint-room  should  not  vary  more  than  j\  inch 
from  the  required  dimensions.  The  spigots  should  be  adjusted  by 
wedges  to  give  a  uniform  joint-space.  The  packing  of  jute  or  other 
material  is  inserted  and  thoroughly  packed  with  a  thin  yarning-iron. 
If  special  strength  is  not  required,  this  packing  may  nearly  fill  the  space 
back  of  the  enlargement  or  V-shaped  space  in  the  bell.  The  remain- 
ing space  is  filled  with  molten  lead.  In  pouring  the  joint  the  lead  is 
guided  into  the  space  by  a  jointer,  commonly  made  of  clay  formed 
around  a  length  of  rope.  This  is  placed  about  the  pipe  so  as  to  press 
against  the  hub,  except  at  the  top,  where  an  opening  is  made  for  pour- 


6o8 


CONDUITS  AND    PIPE-LINES. 


ing.  Patent  jointers  are  better  for  large  pipe  and  difficult  work.  After 
pouring,  the  lead  is  loosened  somewhat  from  the  pipe  by  means  of  a 
chisel  and  set  up  by  calking-iron  and  hammer.  To  do  good  work 
there  should  be  plenty  of  room  around  and  under  the  pipe.  In  wet 
trenches  and  with  small  pipe,  two  or  three  sections  may  be  joined 
before  lowering.  To  handle  large  pipe,  various  forms  of  derricks  are 
employed,  the  three-legged  form  being  commonly  used.  Fig.  164 


Steel  Brahe  Bacn  Cast  iron  BraKe  Stoa, 

FIG.  164. — PIPE-DERRICK,  BALTIMORE,  MD. 

(From  Engineering  Record,  vol.  xxxvn.) 

illustrates  a  specially  designed  derrick  of  the  Baltimore  Water-works, 
made  for  handling  pipe  up  to  16  inches  in  diameter.* 

*  See  also  Eng.  News,  1896,  xxxv.  p.  339,  for  illustration  of  another  form.     ' 


CONSTRUCTION  OF  PIPE-LINES.  609 

637.  Steel  Pipe, — Riveted  pipe  should  be  connected  up  in  as  long 
sections  as  practicable  before  being  transported  to  the  trench,  so  that 
as  much  of  the  riveting  may  be  done  by  power-riveters  as  possible. 
For  this  reason  it  will  be  desirable  on  large  works  to  establish  a  rivet- 
ing and  dipping  shop  not  far  from  the  pipe-line.     In  transportation  and 
construction  the  greatest  care  should  be  taken  to  avoid  injuring  the 
coating.      When  placed  in  the  trench  the  pipe  should  have  an  even 
bearing  on  firm  soil  or  on  blocking,  and  should  be  well  supported  while 
the  joints  are  being  riveted.    The  riveting  is  usually  done  by  hand,  but 
power-riveters  have  been  used  in  a  few  cases.      These  are  made  in  two 
parts:  (i)  a  ring  which  fits  around  the  pipe  and  forms  the  support;  and 
(2)  the  power  appliances,  which  are  placed  on  the  inside.      Two  rivets 
on  opposite  sides   may  be  driven  at  the  same  time.      Power-riveters 
require  a  much  larger  excavation  to  enable  them  to  operate,  but  they 
are  desirable  where  the  rivets  are  large.*     The  percussion  pneumatic 
riveter,  which  is  largely  used  in  ship-building  and  similar  work,  is  well 
adapted  for  this  work. 

After  riveting,  all  field-joints  should  be  calked,  and  these  and  all 
other  abraded  places  painted.  Some  recalking  may  be  needed  after 
the  pipe  is  tested. 

638.  Wooden  Pipe. — Points  to  be  specially  observed  in   the  con- 
struction of  wooden-pipe  lines  are  care  in  the  selection  of  the  timber, 
proper  coating  of  the  bands  and  spacing  of  same,  and  proper  cinching. 
Spacing  of  bands  should  be  fully  indicated  on  the  profile.      In  making 
the  pipe,  the  staves  for  the  lower  half  are  laid  in  a  cradle  of  circular 
form,  and  those  for  the  upper  portion  are  supported  on  rings.      The 
pipe  can  be  built  in  sections,  which  may  readily  be  connected  by  cutting 
the  closing  staves  slightly  too  long  and   springing  them  into  place. 
Sharp  angles  cannot  be  followed,  and  even  to  make  easy  curves  the 
pipe  has  to  be  forced  out  of  line  by  means  of  jacks  and  braced  in  place 
until  the  construction  has  progressed  considerably. 

639.  Testing   and   Inspection — The  pipe   as    completed  should  be 
tested  in  sections  of  1000  feet,  or  thereabouts,  by  hydraulic  pressure. 
For    this    purpose    the    ends  are  closed  with   specially-made   blanks, 
which  are  provided  with  pipe-fittings,  valves,  and  gauge  attachments. 
The  pressure  used  should  be  somewhat  higher  than  that  which  will 
obtain  in  regular  service.     It  may  be  inconvenient  to  leave  a  steel  pipe 
entirely  uncovered  until  the  test  is  made,  on  account  of  trouble  due  to 

*  See  Eng.  News,  1898,  xxxix.  p.   170,  and  Trans.  Am.  Soc.  C.'  E.,  1897,  xxxvm. 
p.  264. 


6 10  CONDUITS  AND    PIPE-LINES. 

temperature  changes,  but  the  field-joints  at  least  should  be  left  open  to 
inspection.      Wherever  leaks  are  found  the  pipe  should  be  recalked. 

After  the  construction  is  completed  a  pipe-line  should,  if  possible, 
be  inspected  in  the  interior  throughout  its  entire  length.  By  suitable 
means  comparatively  small  pipes  can  be  thus  inspected.  A  3<D-inch 
pipe-line  at  Syracuse  was  inspected  by  a  man  passing  through  the  pipe 
by  the  aid  of  a  special  car. 

640.  Covering  of  Pipes. — Except  in  mild    climates    a  conduit  will 
need  to  be  covered  to  prevent  the  water  from  freezing ;  and  even  in 
warm  climates  it  will  usually  be  desirable  to  cover  conduits  of  iron  or 
steel  to  protect  them  from  extreme  variations  of  temperature.      The 
recently  constructed  Coolgardie  pipe-line,   as  first  proposed,  was  to  be 
left  exposed,  on  account  of  the  objectionable  character  of  the  soil,  but 
later  it  was  decided  to  cover  it.     Iron  and  steel  would  be  more  durable 
if  exposed,   as    they  could    then  be  kept  painted,  but  much  expense 
would  be  involved  in  the  construction  of  expansion-joints,  and  there 
would  also  be  more  danger  of  interruption  of  the  supply.    Not  so  much 
objection  is  to  be  made  against  exposed  wooden  conduits,   and  some 
have  been  so  constructed.      In  a  wooden  pipe  there  is  no  trouble  from 
expansion,   and  the  water   is   not   so   greatly   affected   by  temperature 
changes. 

The  depth  of  covering  to  protect  pipes  against  freezing,  in  the  case 
of  the  large  conduits  under  discussion,  need  not  be  more  than  3  or  4 
feet  in  the  northern  part  of  the  United  States.  (See  also  Art.  754.) 
A  covering  of  2  or  3  feet  is  sufficient  to  protect  them  from  injury  by 
ordinary  traffic.  The  maximum  allowable  depth  of  covering  will 
seldom  be  reached,  but  for  very  large  pipes  additional  strength  should 
be  given  when  the  lightest  pipe  would  otherwise  be  used,  if  the  depth 
of  filling  exceeds  15  or  20  feet.  For  the  reasons  pointed  out  in  Art. 
576  the  back -filling  should  be  done  with  great  care  up  to  the  top  of 
the  pipe,  the  material  being  placed  and  tamped  in  4-  to  6-inch  layers. 
This  is  especially  important  for  light  steel  pipe.  If  the  pipe  is  located 
in  paved  streets,  the  back-filling  must  be  thoroughly  tamped  through- 
out (Art.  756). 

Appurtenances  and  Special  Details. 

641.  Provision  for  Expansion  and  Contraction. — In  the  case  of  cast- 
iron  pipes,  expansion  and  contraction  are  sufficiently  provided  for  by 
the  flexibility  of  the  lead  joints,  unless  the  pipe  be  exposed  for  long 
distances.      In  riveted  steel  pipe,  ordinarily  no  provision  for  expansion 
is  made,  the  pipe  being  therefore  stressed  accordingly.      To  resist  the 


APPURTENANCES   OF  PIPE-LINES. 


611 


forces  developed  will  require  heavy  anchorages  at  the  ends  of  pipes 
and  at  junctions  with  masonry  portions,  or  else  expansion-joints  must 
be  used  at  those  places,  as  has  been  done  in  some  instances.  Valves 
and  special  castings  must  also  be  made  strong  enough  to  resist  this 
force  of  expansion.  (See  page  555.)  Exposed  sections  of  pipe,  if  of 
any  considerable  length,  should  be  provided  with  expansion-joints,  but 
as  these  are,  for  large  pipe,  somewhat  expensive  and  difficult  to  make 
operate  satisfactorily,  they  should  be  avoided  if  possible.  For  small 
pipe,  and  at  points  readily  inspected,  the  ordinary  stuffing-box  with 
gland,  etc.,  answers  the  purpose.  For  larger  pipes  various  other  forms 
have  been  devised,  some  of  which  are  illustrated  in  Fig.  165.  Fig. 
165^  illustrates  a  joint  which  has  been  used  to  a  considerable  extent  in 


b  c 

FIG.  165. — FORMS  OF  EXPANSION-JOINTS. 

Paris  with  good  satisfaction.  Figs,  b  and  c  illustrate  joints  wholly  of 
metal  which  have  been  employed  to  some  extent.*  All  these  are 
designed  for  large  pipes. 

642.  Manholes.  — Manholes  should  be  provided  in  large  pipe-lines 
at  intervals  of  500  to  2000  feet,  and  particularly  at  depressions  and 
near  valves.  They  are  usually  of  cast  iron  of  oval  form,  about  1 8  or 
20  inches  long  by  12  or  14  inches  wide.  They  are  bolted  to  cast-iron 
flanges,  which  are  cast  with  or  bolted  to  the  pipe.  Where  it  is  likely 
that  mechanical  scrapers  may  be  used  to  clean  a  pipe,  long  removable 
covers  or  hatch-boxes  should  be  built  at  intervals  to  admit  the  scraping- 
machine.  (See  Chapter  XXIX  for  description  of  such  machines.) 


*  Eng.  News,   1899,  XLI.   p.  406. 
1899,  XL.  p.  156. 


See  also  large  expansion-joint  in  Eng.  Record* 


6l2  CONDUITS  AND    PIPE-LINES. 

643.  Stop-valves. — To  enable  a  pipe-line  to  be  readily  inspected 
and  repaired,  stop-valves  should  be  inserted  at  intervals  of  I  or  2  miles, 
and  especially  at  important  depressions  and  summits.  Otherwise  to 
empty  and  refill  a  long  conduit  would  require  several  days.  In  the 
case  of  breakage,  the  water  can  be  shut  off  at  the  nearest  valve,  and 
any  considerable  waste  or  serious  damage  be  prevented.  Large  valves 
are  expensive,  and  just  as  an  increase  in  the  cost  of  pipe  will  decrease 
the  economical  size  of  pipe,  so  in  the  case  of  valves,  a  size  considerably 
smaller  than  the  pipe  can  often  be  used  with  good  economy.  The 
cost  decreases  rapidly  as  the  size  decreases,  while  the  loss  of  head  due 
to  the  contraction,  if  made  with  suitable  reducers,  is  not  large.  The 
best  size  can  readily  be  calculated  from  cost  of  valves,  cost  of  reducers, 
increased  friction  in  smaller  pipe,  and  cost  of  pumping  or  value  of 
head.  An  advantage  of  the  small  valve  is  that  it  is  much  more  easily 
manipulated,  and  in  some  cases  it  may  be  desirable  to  hold  to  such 
sizes  as  can  be  operated  by  one  man  without  the  use  of  special  gearing. 
An  example  of  such  an  arrangement  is  in  the  connections  of  the  large 
pipes  of  the  East  Jersey  conduit,  where  a  number  of  1 6-inch  pipes  with 
1 6-inch  valves  were  used. 

Valves  up  to  about  16  inches  in  size  are  usually  operated  direct. 
Larger  valves  are  operated  by  gearing,  or  by  hydraulic  power,  the 
cylinder  for  the  latter  being  constructed  as  a  part  of  the  valve.  Large 
valves  are  usually  provided  with  by-passes  which  are  opened  first, 
so  that  the  pressures  on  the  main  valves  are  more  nearly  balanced. 
The  force  required  to  move  a  valve  can  be  roughly  calculated  if  we 
know  the  pressure  and  weight  of  valve-disks.  The  necessary  gearing 
for  manual  operation  can  then  be  calculated.  Very  large  valves  are 
sometimes  divided  into  two  or  more  parts  to  give  easier  handling,  and 
some  are  so  arranged  that  when  operated  a  small  secondary  valve  is  first 
opened  which  acts  like  the  by-pass  to  reduce  the  amount  of  unbalanced 
pressure. 

Valves  of  all  kinds  and  designs  are  furnished  by  various  special 
manufacturing  concerns.  Fig.  166  shows  an  ordinary  single-disk 
valve.  Fig.  167  shows  a  large  valve  with  gearing  and  by-pass  such 
as  is  used  on  the  Boston  water-works.  Valves  for  water-works  should 
have  double-faced  disks,  which  should  seat  readily  and  accurately. 
Many  forms  are  made  with  two  disks  which  adjust  themselves  to  the 
seats.  All  sliding  surfaces  should  be  faced  with  bronze,  and  the  stems 
should  also  be  of  this  material,  and  carefully  proportioned  as  to 
strength.  The  waterway  should  not  be  obstructed  when  the  valve  is 
opened.  All  parts  should  be  readily  removable.  Valves  should  be 


APPURTENANCES   OF  PIPE-LINES. 


6l3 


FIG.  166. — GATE- VALVE 
WITH  SINGLE  DISK. 


FIG.  167.— VALVE  WITH  GEARING  AND  BY-PASS. 


FIG.  168.— VALVE-BOX,  SYRACUSE  WATER-WORKS. 

(From  Trans.  Am.  Soc.  C.  E.,  vol.  xxxiv.) 


614 


CONDUITS  AND    PIPE-LINES. 


thoroughly  tested  for  leakage  from  each  side  with  valve  closed,  and 
again  tested  with  the  valve  open. 

Small  valves  (up  to  16  or  20  inches)  are  placed  vertical,  with  stems 
protected  by  cast-iron  valve-boxes  or  by  masonry  vaults.  Large 
ones  are  placed  horizontal,  with  the  operating  mechanism  surrounded 


Vault  for  16-  to  24-inch  Valves. 
Surface  of  Street.  stltwtoftern  larqtRm.  FStrtet  ffim  - 


Vault  for  30-  to  4O-inch  Valves. 
FIG.  169. — VALVE- VAULTS,  BALTIMORE  WATER-WORKS. 

(From  Engineering  Record,  vol.  xxxvn.) 

by  a  masonry  vault  or  manhole.  The  standard  valve-box  used  at 
Syracuse  is  illustrated  in  Fig.  168,  and  in  Fig.  169  the  valve-vaults 
used  at  Baltimore.* 

644.  Air-valves. — At  every  summit  of  a  pipe-line  and  at  shut-off 
valves  -there  should  be  placed  an  air-valve  to  permit  the  escape  of  air 
on  filling,  the  entrance  of  air  on  emptying,  and  frequently  the  escape 
of  air  which  may  gradually  accumulate  at  summits.  The  first  and 
second  objects  are  readily  obtained  automatically,  and  the  third  often 
is.  Air- valves  are  of  various  design,  a  form  known  as  the  Brooks 
Automatic  Valve  being  illustrated  in  Fig.  170.  This  form  consists  of 
a  brass  disk-valve  supported  on  a  spindle  and  opening  inwards.  When 
there  is  no  water  in  the  pipe  the  valve  remains  open,  but  when  the 
water  reaches  the  valve  as  the  pipe  is  filled,  it  closes  quickly  by  reason 

*  Eng.  Record,  1898,  xxxvn.  p.  143. 


APPURTENANCES   OF  PIPE-LINES. 


6i5 


of  the  buoyant  effect  and  the  velocity  of  the  escaping  water.  A  form 
is  often  used  in  which  a  brass  ball  constitutes  the  valve.  *  For  large 
pipes  a  cluster  of  small  valves  is  employed,  and  it  is  well  to  have  them 
d !.  so  arranged  that  they  will  not  close  simul- 

taneously. The  area  of  air-valves  is  deter- 
mined from  considerations  of  quick  filling,  and 
sometimes  also  is  calculated  to  be  sufficiently 
large  to  admit  air  fast  enough  to  prevent  ex- 
cessive vacuum  in  case  the  pipe  should  be 
broken.  In  distributing  systems,  hydrants  at 
summits'  can  usually  be  used  as  air-valves. 

At  sharp  summits,  and  with  low  velocities 
and  pressures,  air  will  be  apt  to  accumu- 
late and  give  trouble  unless  removed,  especi- 
ally in  the  case  of  force-mains.  Air  can 
be  removed  by  hand-operation  of  valves  of 

the  form  already  des- 
cribed, or  by  automa- 
tic valves.  A  com- 
mon form  of  this  type 
of  valve  is  illustrated 
in  Fig.  171.  It  is  so 
proportioned  that 
when  air  collects  in 
the  chamber  and  the  float  is  no  longer  supported  by  water,  the  valve 
opens  and  permits  air  to  escape  till  the  water  again  rises  to  the  float. 
It  is  necessarily  a  very  small  valve,  and  not  well  suited  for  the  other 
purposes  already  mentioned. t  The  Engineering  Commission  of  the 
Coolgardie  pipe-line  recommended  that  at  important  summits  the  pipe 
should  be  made  of  twice  the  ordinary  size,  so  as  to  facilitate  the  collec- 
tion of  air. 

An  air-valve  is  usually  connected  to  the  main  pipe  by  means  of  a 
short  branch,  which  is  provided  with  an  ordinary  gate-valve  so  as  to 
permit  the  removal  of  the  air-valve  for  repairs.  Air-valves  must  be 
well  encased  and  protected  from  frost. 

645.  Blow-off  Valves. — At  all  depressions,  blow-off  valves  should 
be  provided,  the  waste-pipes  from  which  should  be  led  to  a  sewer, 
stream,  or  drainage-channel.  These  valves  need  be  only  about  one- 
third  the  size  of  the  main  pipe. 


FIG.  170. — AIR-VALVE. 


FIG.  171. 

AUTOMATIC  AIR-ESCAPE 
VALVE. 


*  For  other  designs  see  references  3,  6,  and  7,  p.  627. 

f  See  Eng.  Record,  1899,  XXXIX.  p.  493,  for  description  of  large  automatic  air-valve. 


6i6 


CONDUITS  AND   PIPE-LINES. 


646.  Self-acting  Shut-off  Valves. — Several  English  pipe-lines  have 
been  provided  with  valves  so  arranged  that  in  case  of  accident  to  the 
pipe  they  will  gradually  close  and  so  prevent  loss  of  water  and  the 
destruction  of  property  by  flooding.      In  the  device  used,  a  lever  carries 
at  one  end  a  small  disk  placed  in  the  centre  of  the  pipe.     If  the  velocity 
of  the  water  exceeds  a  certain  amount,  the  pressure  on  this  disk  moves 
the  lever,   thus  releasing  a  weight  which  in  turn  operates  a  butterfly 
valve  in  the  main  pipe.* 

647.  Check- valves. — These  are  introduced  at  points  where  a  break- 
age would  permit  a  large  loss  of  water  by  backward  flow,  such  as  at 
the  entrance  to  reservoirs,  at  the  foot  of  long  upward  inclines,  and  in 
force-mains  just  beyond  the  pumps.     Their  use  in  connection  with  the 

circulation  in  reservoirs  is  mentioned  in  Art. 
707.  Fig.  172  illustrates  an  ordinary  check- 
valve  for  small  pipes.  For  pipes  larger  than 
24  to  30  inches  a  diaphragm  or  valve-plate  is 
cast  in  an  enlarged  section  of  the  pipe,  and  a 
number  of  small  valves  attached  to  this  plate, 
the  total  area  of  valves  usually  exceeding 
that  of  the  pipe.  A  small  by-pass  is  also 
provided  to  avoid  heavy  water-hammer. 

648.  Pressure-regulating  Devices. — Various  methods  of  automatically 
regulating  the  pressure  are  employed  in  different  places.      One  very 
desirable  method  of  regulating  the  pressure  in  a  long  conduit  is  by 
means  of  reservoirs  and  open  stand-pipes,  as  already  noted  (Art.  629). 
These  structures  must  be  provided  with  overflows,  and  if  the  demand 
is  quite  irregular  and  the  stand-pipe  small,  much  water  is  likely  to  be 
wasted.      This   waste   can   be   avoided   and   the   flow   adjusted  to   the 
demand    by  the    use  of  the  balanced    float-valve,   described  on  page 
48 1. 1     By  this  means  the  level  in  the  reservoir  may  be  kept  constant 
by  varying  the  opening  in  the  preceding  section  of  pipe.     This  method 
is  applicable  where  a  pipe-line  is  divided  into  several  levels,  or  where 
a  low-level  district  is  served  from  a  high-level  source,  but  the  section 
of  pipe-line  leading  to  such  valve  must  be  designed  for  static  pressure. 

By  suitable  arrangements  the  balanced  valve  may  be  used  also  as  a 
pressure-regulator,  or  pressure-reducer,  without  the  interposition  of  a 
reservoir.  To  accomplish  this  the  valve  (see  Fig.  135,  page  486)  may 

*  Proc.  Inst.  C.  E.,  vol.  cxxvi.  p.  2. 

fSee  description  of  special  arrangement  of  such  a    valve,  in  Eng.  News,  1898, 
XL.  p.  158. 


FIG.  172. — CHECK-VALV 


APPURTENANCES   OF  PIPE-LINES.  6l/ 

be  operated  by  a  small  piston,  d,  acting  in  a  closed  cylinder.  On  one 
side  of  the  piston  this  cylinder  is  arranged  to  communicate  with  the 
main  pipe  at  whatever  point  the  pressure  is  to  be  regulated.  Upon  the 
other  side  of  the  piston  a  spring  acts  in  opposition  to  the  water- 
pressure,  which  spring  may  be  adjusted  to  any  given  tension.  So  long, 
then,  as  the  pressures  of  the  water  and  spring  are  equal  no  movement 
takes  place,  but  as  soon  as  the  water-pressure  exceeds  that  of  the 
spring  the  valve  is  moved,  which  either  increases  or  decreases  the 
discharge  as  the  case  may  be,  and  again  brings  the  pressure  down  to 
the  normal  amount.  A  flexible  diaphragm  of  thin  metal  may  be  used 
in  place  of  the  piston. 

Safety-valves,  or  pressure- relief  valves,  are  occasionally  used  at  the 
ends  of  long  pipe-lines  or  wherever  water-hammer  is  especially  to  be 
feared.  They  are  simple  disk  valves  opening  outwards  and  held  in 
place  by  springs  which  are  adjusted  to  the  water-pressure.  They 
should  be  of  large  section  and  designed  with  reference  to  the  principles 
discussed  in  Art.  279,  page  252.  They  take  the  place  of  air-chambers, 
and  are  more  convenient  at  points  where  air-chambers  could  not  readily 
be  kept  full  of  air.  The  water  which  passes  through  them  at  times  of 
excessive  pressure  is  of  course  wasted.  The  balanced  valve  can  also 
be  readily  used  as  a  safety-valve  by  the  method  described  in  the  pre- 
ceding paragraph.* 

649.  Terminal  Arrangements. — The  upper  end  of  a  gravity  pipe-line 
is  usually  enclosed  in  masonry  and  provided  with  a  sluice-gate  or 
valve.  At  this  point  it  is  also  desirable  to  have  a  weir  or  measuring- 
sluice.  If  pumps  are  employed,  then  a  Venturi  meter  is  a  valuable 
device  for  measuring  the  flow.  The  lower  end  of  a  pipe-line  usually 
terminates  in  a  reservoir,  where  again  valves  are  provided  and  where 
connections  may  also  be  made  directly  with  the  pipe  system.  In  case 
the  pipe-line  is  designed  according  to  the  hydraulic  grade-line,  no 
valves  should  be  placed  here,  or  if  so  placed,  should  be  interlocked  with 
waste-valves,  so  that  the  latter  must  be  open  before  the  former  are 
closed.  Such  interlocked  valves  were  used  on  the  East  Jersey  pipe- 
line. 

Intermediate  stand-pipes  and  reservoirs  at  the  hydraulic  grade-line 
may  be  merely  short  open,  pipes  placed  vertically,  or  laid  up  an 
adjacent  hillside  till  they  reach  the  proper  elevation  and  where  provision 
is  made  for  overflow;  or  they  may  be  larger  or  smaller  reservoirs, 
according  to  the  necessity  for  storage.  It  may  be  better  and  more 

*  See  details  of  such  a  valve   used   on   the  East  Jersey  pipe-line.     Eng. 
1893,  xxx.  p.  24. 


6l8  CONDUITS  AND  PIPE-LINES. 

convenient  to  store  water  in  three  or  four  reservoirs  than  in  a  single 
one.  Rochester  has  two  such  reservoirs.  Liverpool  has  six  reservoirs  on 
a  67-mile  pipe-line,  of  capacities  ranging  from  2^-  million  to  650  million 
gallons.  One  advantage  of  large  reservoirs  is  that  the  pressures  are 
kept  more  constant  without  overflow,  or  with  a  less  frequent  adjustment 
of  valves.  Automatic  valves  may  be  used  as  described  in  Art.  648. 

650.  Crossings. — In  crossing  under  other  structures,  such  as  rail- 
ways, buildings,  sewers,   etc.,  special  precautions  should  be  taken  to 
avoid  all  danger  of  future  breakage.      Pipe  of  extra  strength  may  be 
used,  or   added   strength  given  by  a  bed   and   covering   of  concrete. 
Large  pipe-lines  should  be  divided  into  two  smaller  ones  for  safety, 
with  valve-connections  at  the  ends.      In  very  important  cases  the  pipe 
may  be  laid  in  a  subway  so  as  to  permit  of  repairs  as  readily  as  else- 
where.     Streams  are  crossed  either  on  bridges,  or  by  laying  the  pipe 
beneath  the  stream-bed,  or  by  the  use  of  a  subway  as  above  mentioned. 
At  Cleveland,  Ohio,  several  crossings  of  narrow  navigable  streams  have 
been  changed  to  tunnel-crossings  so  as  to  permit  of  repairs.      These 
tunnels  are  about  600  feet  long  and  9^  feet  in  diameter,  and  are  located 
78  feet  below  the  street-surface.      They  end  in  vertical  shafts  provided 
with  manholes.      The   pipes  are  of  steel,  48   inches   in   diameter,  the 
vertical  sections  of  which  are  supported  upon  I  beams  built  in  the  shaft. 
Expansion-bearings  are  provided  at  the    bottom,   and  the  horizontal 
portions  are  supported  on  saddles  6  feet  apart.  *    Many  examples  of  this 
form  of  crossing  exist  in  European  works,  such  as  the  Mersey  crossing 
of  the  Liverpool  aqueduct,  and  the  crossing  of  the  Seine  at  Paris.. 

In  this  country  the  common  practice  in  crossing  a  stream  is  to  lay 
a  cast-iron  or  steel  pipe  below  the  stream-bed,  or  else  to  employ  a 
bridge-crossing.  Where  no  bridge  already  exists  the  former  will 
ordinarily  be  the  cheaper,  and  in  many  cases,  as  in  navigable  channels, 
a  bridge  could  not  be  permitted.  In  other  cases  it  may  be  cheaper  to 
build  a  bridge  especially  for  this  purpose,  as  in  rocky  canyons  and 
narrow  gorges.  At  the  angles  at  ends  of  bridge-  and  submerged 
crossings  special  care  is  necessary  to  keep  the  pipe  from  separating  at 
the  joints. 

651.  Bridges. — If  the  pipe-line  crosses   an  existing   bridge,  it  will 
usually  be  convenient  to  support  it  beneath  the  flooring.      Where  a 
bridge  is  built  for  the  purpose,  no  floor-system  is  put  in,  but  merely 
suitable  straps  or  stirrups  to  support  the  pipe.      Steel  or  .wood-stave 
pipe  may  be  used  for  short  spans  without  other  support  than  that  fur- 

*  Eng.  Record,  1898,  xxxvm.  p.  449. 


EXPOSED   PIPES.  619 

nished  by  the  pipe  itself.  A  steel  pipe  \  inch  thick,  full  of  water,  will, 
at  a  -fibre-stress  on  gross  section  of  10,000  pounds  per  square  inch, 
span  a  length  of  about  65  feet,  if  the  tendency  to  buckle  is  not  taken 
into  account.  This  span-length  is  nearly  independent  of  the  diameter 
of  the  pipe,  varying  directly  with  the  thickness  of  the  material;  but 
with  large  diameters  the  allowable  stress  would  have  to  be  much 
reduced,  or  else  provision  made  to  stiffen  the  upper  plates  of  the  pipe. 
The  pipe  can  readily  be  stiffened  by  the  use  of  angles  riveted  along 
the  upper  surface,  and  also  by  placing  the  longitudinal  seams  near  the 
top.  If  a  pipe  is  used  as  a  bridge,  the  circular  seams  must  be  designed 
for  the  extra,  stress  involved.  Expansion  can  be  provided  for  in  such 
a  bridge  by  resting  the  pipe  at  one  end  in  a  saddle  which  is  sup- 
ported on  rollers.  An  expansion-joint  is  then  placed  just  back  of  this 
saddle.  A  pipe  bridge  would  be  cheaper  than  a  separate  structure 
even  if  the  metal  had  to  be  much  thickened  to  give  the  necessary 
strength.  The  pipe  can  also  be  advantageously  curved  so  as  to 
constitute  an  arch  bridge.  This  is  a  common  practice  in  Europe, 
where  spans  of  more  than  150  feet  have  been  built  in  this  way. 
The  method  has  also  been  used  in  the  new  Weston  aqueduct, 
where  an  arch  span  of  So  feet  has  been  made  of  a  go-inch  pipe.* 
Wood-stave  pipe  has  also  been  used  in  this  way  for  spans  of  over 
100  feet,  f 

652.  Protection  of  Exposed  Pipes.  —  The  amount  of  protection 
required  to  prevent  freezing  on  bridges,  or  at  other  exposed  places, 
depends  upon  the  size  of  pipe,  the  amount  of  circulation  during  periods 
of  minimum  flow,  the  temperature  of  the  air  and  the  water,  and  upon 
the  length  of  the  exposed  portion.  No  general  rule  can  be  given. 
Usually  the  water  is  from  surface  sources,  and  its  temperature  in  winter 
will  be  but  little  above  the  freezing-point,  unless  it  should  pass  for  long 
distances  in  deep  trenches.  The  temperature  of  the  water  will  change 
very  slowly  in  large  pipe-lines,  and  in  the  case  of  pipes  2  feet  or  more 
in  diameter  special  protection  would  seldom  be  needed  at  crossings  of 
ordinary  length,  if  the  water  has  at  all  times  some  movement.  A 
wooden  pipe  possesses  much  advantage  in  this  respect  over  pipes  of 
iron. 

Small  lines,  especially  distributing-mains,  require  protection.  This 
is  usually  furnished  by  placing  the  pipe  in  a  wooden  box  and  filling 
around  it  with  some  non-conducting  substance,  such  as  sawdust, 


*  Eng.  Record,  1904,  XLIX.  p.  480. 

t  Trans.  Am.  Soc.  C.  E.,  1894,  xxxi.   p.  135. 


620  CONDUITS  AND    PIPE-LINES. 

mineral  wool,  asbestos,  hair-felt,  and  the  like.  A  mixture  of  plaster 
of  Paris  and  sawdust  has  been  used  with  good  results.  Any  packing 
to  be  effective  should  be  kept  dry.  The  packing  is  often  arranged  to 
give  one  or  more  dead-air  spaces  around  the  pipe  to  aid  in  preventing 
radiation. 

Materials  such  as  above  mentioned  act  to  retain  the  heat  of  the 
water ;  but  if  the  water  is  already  near  the  freezing-point,  they  are  not 
very  efficient.  Some  method  of  applying  heat  may  be  desirable. 
Mr.  S.  E.  Babcock  has  successfully  solved  this  problem  in  the  case  of 
an  exposed  pipe  at  Little  Falls,  N.  Y.,  by  the  use  of  wool  waste  as 
packing.  This  material  contains  a  small  amount  of  oil  and  gradually 
decomposes,  thus  giving  off  a  small  amount  of  heat.  It  was  found 
necessary  to  renew  this  packing  in  five  years,  but  the  expense  was 
small.* 

653.  Submerged  Pipes, — Various  methods  are  employed  in  laying 
pipes  beneath  watercourses.  In  the  case  of  small  streams  the  usual 
method  is  to  employ  a  coffer-dam  and  lay  the  pipe  as  on  dry  land. 
Where  the  water  cannot  readily  be  excluded  in  this  way  the  pipe  must 
either  be  put  together  before  lowering  in  place  or  must  be  laid  by 
divers.  Submerged  pipe  should,  as  a  rule,  be  laid  in  a  trench  and 
carefully  covered  to  prevent  injury  by  waves,  drift,  ice,  boats,  etc. 
The  trenching  is  done  by  dredging,  and  any  drilling  and  blasting  which 
may  be  necessary  can  be  done  from  platforms  or  from  anchored  barges. 
In  the  case  of  at  least  one  pipe-line  the  trench  was  made  by  the 
scouring  action  of  the  water,  which  was  forced  to  flow  beneath  the  pipe 
as  it  was  gradually  lowered  into  place,  t  The  trench  should  be  formed 
to  line  and  grade,  or  at  least  an  accurate  profile  of  the  same  should  be 
taken. 

Various  special  details  are  used  in  submerged-pipe  laying,  such  as 
the  various  forms  of  flexible  joints  to  enable  the  pipe  to  conform  to  the 
grade  of  the  trench,  and  special  joints  for  easy  connection  where  divers 
are  employed.  Submerged  pipe  should  be  thoroughly  tested  either  in 
sections  before  laying,  or  better,  after  the  line  is  completed,  in  which 
case  compressed  air  can  be  used  for  the  purpose.  Leakage  of  air  will 
be  indicated  by  the  appearance  of  bubbles,  and  the  imperfect  joints  can 
then  be  calked  by  divers.  The  various  methods  of  laying  submerged 
pipe  will  now  be  described  together  with  some  of  the  special  details 
used  in  this  work. 

*  Proc.   Am.  W.  W.    Assn.,    1892,    p.    no.     See   also   description    of   boxing   at 
Duluth,  in  Eng.  Record,  1899,  xxxix.  p.  162. 
\  Eng.  News,  1892,  xxvu.  p.  424. 


SUBMERGED    PIPES. 


621 


1.  Where  the  stream  is  shallow,  a  common  method  of  laying  is 
first  to  connect  the  entire   pipe,  or   large  sections  of  it,  on  platforms 
extending  across  the  stream,  and  to  lower  the  portion  so  connected  by 
means  of  screws.      Ordinary  joints  can  usually  be  employed  and  the 
pipe  put  together  to  fit  the  profile  of  the  trench.      Pipes  can  very  con- 
veniently be  laid  in  this  way  from  the  ice  during  winter. 

Two  cases  of  this  method  of  laying  will  be  briefly  noted.  At  Cedar  Rapids, 
la.,  600  feet  of  1 6-inch  pipe  was  laid  in  this  way  in  a  depth  of  2\  feet  of 
water.  A  trench  2  feet  deep  was  first  excavated,  and  framed  trestle-bents  set 
up  1 2  feet  apart.  A  barge  was  then  run  between  the  legs  of  the  trestles,  .the 
pipe  put  together  on  the  barge,  and  then  slung  by  straps  fastened  to  i^-inch 
threaded  rods  suspended  from  the  trestles.  When  the  entire  pipe-line  was 
connected,  it  was  all  lowered  together,  electric-bell  signals  being  used  to 
secure  simultaneous  action  among  the  several  men  stationed  at  the  screws. 
The  cost  of  laying  was  $1.25  per  foot.* 

At  Escanaba,  Mich.,  2000  feet  of  12 -inch  wrought-iron  pipe  was  lowered 
through  ice  at  a  cost  of  $200.  The  trench  was  excavated  in  sand  by  means 
of  the  water-jet,  after  the  pipe  was  laid.f 

Where  the  pipe  cannot  readily  be  built  to  conform  to  the  trench, 
or  where  settlement  is  feared,  a  certain  number 
of  flexible  joints  may  be  used.      The  most  com- 
mon   form  is    the  Ward  joint,  designed  by  Mr. 
J.  F.  Ward  many  years  ago.      It  is  illustrated  in 
Fig.  1/3-      To  make  the  joint  tight  requires  that 
some  tension  be  put  upon  the  pipe  after  the  joint 
is  in  place.      Other  forms  of  flexible  joints  are  i 
illustrated  on  the  following  pages. 

2.  Instead  of  connecting  the  entire  pipe-line    FIG.  173.— WARD  FLEXI- 
and  lowering  all  together,  it  may  be  lowered  in  BLE  JOINT. 
sections  by  the  aid  of  flexible  joints,  each  section  consisting  of  several 
lengths  of  pipe  connected  in  the  usual  manner.      The  pipe  can  thus  be 
laid  and  lowered  from  a  short  piece  of  trestle  or  from  a  barge.      This 
method   is   especially  suitable   for   deep   water   where   trestles   cannot 
readily  be  used. 

At  Portland,  Oregon,  a  28-inch  cast-iron  pipe  was  laid  from  barges  and 
trestles,  the  former  being  used  in  deep  water  and  the  latter  in  shallow  water. 
The  pipe  was  lowered  from  the  barge  by  sliding  it  down  a  cradle  extending 
from  the  barge  to  the  river  bottom.  Flexible  joints  were  used  throughout.! 

At  Columbus,  Ga.,  an  1 8-inch  main  was  laid  by  the  use  of  twenty-four 
flexible  joints.  The  pipe  was  put  together  on  shore  in  204 -foot  sections, 

*  Eng.  Record,  1898,  XXXVII.  p.  97. 
|  Eng.  Record,  1899,  XL.  p.  72. 

\  Trans.  Am.  Soc.  C.  E..  1895,  xxxin.  p.  257.  Several  flexible  joints  are  here 
described. 


622 


CONDUITS  AND    PIPE-LINES. 


each  terminating  in  one-half  of  a  flexible  joint.  The  sections  were  floated 
into  place  one  by  one,  connected  to  the  end  of  the  previously  laid  portion 
and  then  sunk.  All  leaky  joints  were  afterwards  calked  by  divers.* 

At  Rochester,  N.  Y.,  a  6o-inch  steel  intake-pipe  was  laid  in  sections  100 
feet  long,  joined  by  means  of  flexible  joints.  The  pipe  was  connected  above 
water  and  lowered  joint  by  joint  by  means  of  winches  supported  on  pile  plat- 
forms. The  joint  used  was  similar  to  that  shown  in  Fig.  i74.f 

3.  Many  lines  of  submerged  pipe  have  been  laid  by  joining  several 
lengths  on  shore,  towing  them  into  position,  sinking  them  and  connect- 
ing them  by  divers.  This  method  is  especially  applicable  for  large 
pipe-lines.  It  has  been  used  for  large  intakes  at  Syracuse  and  at 
Milwaukee;  also  at  Galveston,  Nashville,  Boston,  and  many  other 
places. 

The  method  of  laying  the  Syracuse  intake  was  as  follows:  J  The  52-inch 
pipe  was  first  riveted  together  in  sections  116  feet  long.  The  ends  of  these 
sections  were  then  closed  with  oiled  canvas  bulkheads,  rolled  into  the  water, 
and  floated  to  a  position  between  the  sections  of  a  catamaran  stationed  over 
the  pipe-trench  and  held  in  place  by  spud-piles.  Ropes  were  then  attached 
to  the  pipe,  the  bulkheads  removed,  and  the  pipe  lowered  to  rest  upon  small 
timber  foundations  secured  to  the  pipe  before  sinking.  The  joining  was  done 
by  a  diver.  The  special  joint  used  in  connecting  the  sections  is  illustrated  in 
the  right-hand  portion  of  Fig.  174.  A  cast-iron  hub  is  riveted  to  the  end  of 


FIG.  174. — FLEXIBLE  AND  RIGID  JOINTS,  SYRACUSE  INTAKE. 

one  section,  and  through  this  pass  twenty  hook -bolts.  After  guiding  the  pipes 
into  place  these  hooks  are  brought  to  bear  against  a  loose  hoop  of  wrought 
iron  placed  on  the  end  of  the  other  section,  and  the  nuts  screwed  up,  thus 
closing  up  a  lead-pipe  gasket  and  forming  a  tight  joint.  Several  flexible 
joints  were  used  at  changes  of  grade,  and  one  of  these  is  also  illustrated  in  the 
figure.  It  is  made  by  joining  short  pieces  of  pipe  by  a  very  broad  lead  joint 
run  into  the  space  between  the  two  4-inch  channels  and  a  cast-iron  spigot. 
A  i2-degree  deflection  is  permitted.  The  cost  for  the  pipe  delivered  was 


*  Eng.  Record,  1899,  XL.  p.  97. 

t  Eng.  News,  1895,  xxxm.  p.  234. 

\  Trans.  Am.  Soc.  C.  E.,  1895,  xxxiv.  p.  23. 


SUBMERGED   PIPES, 


623 


$8.80  per  foot,  including  seven  flexible  joints.  The  laying  (exclusive  of 
trenching)  cost  $2.50  per  foot. 

Similar  joints  were  used  on  the  Duluth  intake  at  a  cost  of  $82.00  each  for 
the  rigid  joints,  and  $398.25  for  the  flexible  joints.  The  6o-inch  pipe  there 
used  cost  $9. 1 1  per  foot  delivered.  Flexible  joints  very  similar  in  design 
have  also  been  used  at  Toronto  and  at  Rochester,  N.  Y.,  as  already  noted. 

The  6o-inch  cast-iron  intake  at  Milwaukee  was  laid  in  5o-foot  lengths  and 
joined  by  a  diver.  The  spigot  end  of  each  section  was  fitted  with  a  temporary 
hub  and  poured  with  lead  before  it  left  shore.  After  entering  it  into  the  hub 
of  the  previously  laid  section  it  was  then  pulled  tight  by  means  of  clamps  as 
illustrated  in  Fig.  175.  As  much  as  200  feet  of  pipe  per  day  was  laid  by  this 
method.* 


FIG.  175. — JOINT  FOR  CAST-IRON  INTAKE, 
MILWAUKEE. 


FIG.  176. — FLEXIBLE  AND  TAPER  JOINTS, 
BOSTON. 


In  laying  submerged  pipe  under  the  Charles  River,  Boston,  three  types  of 
joints  were  used  :  (i)  the  ordinary  joint  with  three  turned  grooves  in  the 
bell  instead  of  one;  (2)  a  taper  joint  for  making  subaqueous  connections;  and 
(3)  a  flexible  joint.  The  last  two  are  illustrated  in  Fig.  176.  In  making  the 
taper  joint  the  sections  are  put  together,  the  joint  run  with  lead,  then  the 
sections  drawn  apart,  leaving  the  lead  in  place.  A  similar  form  of  joint  has 
been  used  in  many  places.  In  the  flexible  joint  the  spigot  is  turned  to  a 
spherical  surface  and  cut  off  so  as  to  permit  a  deflection  of  i  in  10  without 
projecting  into  the  waterway.  It  comes  in  contact  with  a  rib  on  the  bell 
turned  to  a  close  fit.  In  laying,  the  pipes  were  put  together  on  a  platform 
on  shore  in  sections  of  6  or  7  lengths*  then  towed  in  place  and  sunk.  They 
were  adjusted  according  to  the  direction  of  a  diver,  and  the  sections  drawn 
together  by  a  hydraulic  cylinder  attached  to  the  pipe  already  laid.  The  joints 
were  calked  by  the  diver.  Flexible  joints  were  used  where  there  were 
vertical  deflections,  or  where  settlement  was  to  be  feared,  f 

4.  A  method  of  laying  submerged  pipes  sometimes  used  is  to  con- 
nect the  entire  pipe,  or  sections  of  it,  on  shore  in  a  line  in  the  direction 
of  the  proposed  main,  and  to  haul  the  pipe  into  the  stream  by  a  winch 


*  Eng.  News,  1895,  xxxiv.  p.  187. 
f  Eng.  Record,  1898,  xxxvil.  p.  518. 


624  CONDUITS  AND    PIPE-LINES. 

.on  the  opposite  side,  the  pipe  being  at  the  same  time  floated  by  lash- 
ing it  to  empty  barrels.  At  the  Mersey  River  crossing  of  the  Liver- 
pool line  a  temporary  pipe  was  laid  by  riveting  up  complete  a  1 2-inch 
steel  pipe  and  hauling  the  entire  main  across  at  one  operation. 
In  this  method  flexible  joints  should  be  used  in  sufficient  number  to 
permit  of  all  necessary  deflections  from  a  straight  line. 

5.  Very  short  crossings  of  deep  channels  may  often  be  conveniently 
made  by  riveting  up  the  pipe  and  sinking  the  entire  structure  at  one 
operation.  This  method  avoids  obstructing  the  channel  for  any 
considerable  time,  and  has  been  used  in  the  case  of  several  narrow 
navigable  streams. 

COST    OF    AQUEDUCTS   AND    PIPE-LINES. 

654.  Canals  and  Masonry  Aqueducts — The  cost  of  conduits  of  this 
class  can  be  quite  closely  estimated,  if  constructed  in  ordinary  ground, 
from  an  itemized  estimate  of  quantities,  the  unit  prices  being  about  the 
same  as  noted  on  pages  371  and  409.     The  unit  prices  used  by  Freeman 
in  the  report  already  referred  to  were  based  on  the  actual  cost  of  the 
large  Wachusett  aqueduct  of  Boston.      They  were: 

For  Aqueducts  in  Cttt-and-cover  : 

Earth  excavation $0.35  per  cubic  yard. 

Earth  borrow 0.30  "  "  " 

Rock  excavation 1.50  "  "  " 

Portland-cement  concrete 6.00  "  "  " 

Natural-cement  concrete 5.00  "  "  " 

Brick  lining 13.00  "  "  " 

for    Tunnels  : 

Heading  excavation 7.00  "  "  " 

Bench  excavation 4.00  "  "  " 

Brick  lining 013.00  "  "  " 

Brick  backing 6.50  "  "  •' 

Rubble  backing 4.00  "  "  " 

Dry  backing 2.00  "  "  •• 

Portland-cement  concrete  in  side  lining S.oo  "  "  " 

Natural-cement  concrete  in  side  lining 6.50  "  "  " 

The  Sudbury  aqueduct  of  a  cross-section  equivalent  in  area  to  a 
circle  8£  feet  in  diameter  cost  $23.86  per  foot,  excluding  special  struc- 
tures. The  Wachusett  aqueduct  cost  about  $24.00  per  foot.  Its 
cross-section  is  equal  to  a  circle  of  11.33  feet  in  diameter. 

655.  Pipe-lines. — The  cost  of  pipe-lines  will  vary  greatly  according 
to  the  cost  of  the  material  used.      This  element  can  readily  be  ascer- 
tained at  any  time  by  reference  to  current  price-lists,  and  the  item  of 


COST  OF  AQUEDUCTS  AND   PIPE-LINES. 


625 


transportation  can  also  be  quite  easily  determined.  For  a  good 
detailed  analysis  of  amount  and  cost  of  labor,  reference  may  be  made 
to  Weston's  "  Tables  for  Estimating  the  Cost  of  Laying  Cast-iron 
Water-pipe,"  also  to  Billing's  "  Details  of  Water-works  Construc- 
tion," and  to  contract  prices  in  the  current  periodicals.  The  data  here 
given  are  intended  only  to  give  a  general  notion  of  the  relative  cost  of 
work  of  this  character.  The  formula  already  given  (page  604)  for  the 
approximate  cost  of  cast-iron  pipe,  furnished  and  laid,  is 


C  =  20  -f- 


where  c  =  cost  per  foot  in  cents,  a  —  cost  of  pipe  per  pound,  d  — 
diameter  of  pipe  in  inches.  This  formula  has  reference  to  work  done 
under  average  conditions,  and  for  earth-excavation,  and  refers  only  to 
ordinary  sizes  of  pipe.  From  this  formula  the  cost  of  various  sizes  is 
as  follows: 


Size  of  Pipe. 

Cost  per  Foot. 

Cost  of  Pipe 
=  i  cent  per  Ib. 

Cost  of  Pipe 
=  i£  cents  per  Ib. 

4-inch  '       .... 

$0.37 
•52 
.70 
.91 
I.I4 
1.67 
2.28 
2.96 

$0.46 
.68 

•95 
1.26 
1.61 
2.40 
3-32 
4-33 

6-          

8.          

10-         

12-             

16- 

9A- 

These  figures  are  not  intended  to  include  the  items  of  contractors' 
profit  and  of  engineering. 

The  actual  cost  per  foot  of  pipe,  for  distributing  pipes,  valves,  etc., 
at  Plainfield,  N.  J.,  is  given  as  follows:* 


6-in. 

8-in. 

iz-in. 

i6-in. 

Pipes  and  specials  

So    ^Qd, 

$o  561 

8>o  06  <s 

$1    <%8o 

O<1 

rjeo 

087 

•  OO7 

OJ.I 

CKO 

oc/i 

•yy/ 

•  O72 

Tools  and  labor 

j  2/1 

i6<; 

T77 

260 

Contractor  and  engineering 

O3A 

06-* 

OO  I 

O8O 

Total  

$o.6-*i 

$0.889 

$1  .^dd. 

$2    Oo8 

*  Trans.  Am.  Soc.  C.  E.,  1894,  xxxi.  p.  375. 


626 


CONDUITS   AND    PIPE-LINES. 


A  similar  statement  for  Alliance,  Ohio,  shows  very  nearly  the  same 
cost.* 

In  large  cities  where  pavements  are  disturbed  and  the  price  of 
labor  is  high,  the  cost  of  pipe-laying  is  likely  to  be  considerably  more 
than  given  above. 

For  very  large  cast-iron  pipes  the  cost  of  the  iron,  lead,  and  trans- 
portation forms  such  a  large  proportion  of  the  total  cost  that  a  relatively 
close  estimate  can  be  made  when  these  items  are  once  known. 

Table  No.  78,  compiled  by  Adams, t  aims  to  give  comparative 
figures  for  the  cost  of  wood-stave,  steel,  and  cast-iron  pipe.  The 
figures  are  based  on  a  cost  of  cast-iron  pipe  of  $19.00  per  ton,  and  of 
steel  of  1.6  cents  for  No.  14  B.  W.  G.  plate  to  1.25  cents  for  No.  8 
and  thicker.  These  prices  are  exceptionally  low.  They  are  now 
(1901)  much  higher,  and  the  figures  of  the  table  should  be  correspond- 
ingly raised.  The  costs  as  given  do  not  include  hauling  nor  con- 
tractors' profits;  they  are  intended  to  be  used  for  comparative  purposes 
only. 

TABLE   NO.  78. 

COMPARATIVE    COST    OF    PIPE    AT    CHICAGO    (ADAMS). 
(Including  Laying,  but  not  Hauling.) 


Stave. 

Steel  Riveted. 

Cast  Iron. 

d 

i 

O 

O 

o 

d 

d 

5 
1 

i 
1 

T3 
rt 
U 

E 

•O  ' 
05 
V 

'E 

i 

u 

E 

M 

CQ 

PQ 
o~ 

ed 

00 

n 

a 

jq 
O 

. 

E 

1 

I 

1 

+J 

1 

1? 

1 

8 

8  . 

d 

d 

& 

i 

0 

i 

5 

a 

X 

° 

2 

I 

12.  . 

.42 

•49 

.63 

.85 

•32 

•38 

.44 

•  73 

•  77 

.84 

1.  00 

18.. 

.69 

.So 

i.  02 

1.46 

•57 

.65 

.78 

.98 

.... 

.... 

1.29 

i«35 

1.46 

1.70 

24 

•79 

.91 

1.14 

i.bi 

.... 

•85 

1.04 

1.28 

1.55 

1.99 

.  .  .  . 

1.91 

2.OO 

2.18 

2-55 

30.. 

.96 

I.  12 

1.44 

2.06 

.... 

.... 

.... 

1.27 

1-59 

1.93 

2.46 

3-04 

2.67 

2.80 

3.07 

3-6i 

36.. 

1.19 

1.40 

1.82 

2.65 

.... 

.... 

1.55 

1.93 

2.30 

2.92 

3.58 

3.47 

3.67 

4.06 

4-85 

42.. 

1.40 

1.68  2.23 

3-33 

.... 

.  .  .  . 

.... 

1.61 

2.18 

2.66 

3-37 

4.12 

4.42 

4.69 

5.22 

6.28 

48., 

1.55 

1.85 

2.46 

3-67 

.... 

.  .  .  . 

.... 

.... 

2.48 

3.03 

3-83 

4.66 

5.50 

5.84 

6.53 

7.92 

54" 

2.23 

2.62 

3-43 

5-02 

.... 

... 

2.80 

3.414.29 

5.21 

6.65 

7.10 

8.00 

9.78 

60.. 

2.85 

3-35 

4-37 

6.40 

.... 

.  .  .  . 

.  .  .  . 

3-79 

4-75 

5-74 

8.04 

8.63 

9.80 

12.13 

66.. 

3.21 

3.8i 

5-00 

7.38 

.... 

.... 

4-35 

5.21 

6.29 

9.51 

10.  16 

n.55 

14.05 

72.  . 

3.65 

4.38 

5.83 

8.27 

.... 

.... 

.... 

.... 

... 

4-52 

5.66 

6.83 

11.32 

I2.OO 

13.26 

16.00 

Regarding  the  actual  cost  of  steel  pipe-lines  the  following  data  are 
given : 


*  Eng.  News,  1894,  xxxi.  p.  490. 

f  Trans.  Am.  Soc.  C.  E.,  1899,  XLI.  p.  58. 


LITER  A  TURE.  627 

The  Rochester  38-inch  steel  conduit,  26  J  miles  long,  built  in  1894, 
cost  about  $8.10  per  foot,  ready  for  use.  The  pipe  was  composed  of 
J->  -rV>  and  f-inch  plates  with  lap-joints.  The  4O-inch  steel  pipe  for 
Cambridge,  Mass,  built  in  1895,  4.6  miles  long,  cost  $4.81  per  foot, 
or  3.13  cents  per  pound.  The  pipe  thickness  was  T%  inch,  and  lap- 
joints  were  used.  The  contract  price  of  the  Allegheny  6o-inch  steel 
pipe  was  about  $8.50  per  foot.  The  plates  were  J-inch  thick.  The 
pipe  was  built  in  1896.  Bids  for  the  New  Bedford  48-inch  steel-pipe 
line  in  1896  were,  for  the  pipe  alone,  $5.10  per  foot  for  lap-joints  and 
$5.65  for  butt-joints  and  countersunk  rivets.  The  plates  were  TVmch 
thick,  and  length  of  line  8  miles.  For  the  conduit  complete  the  corre- 
sponding prices  were  $7.55  and  $8.10  respectively. 

Freeman  estimates  the  cost  of  steel-pipe  conduits  of  f-inch  metal 
for  New  York  City  as  follows  :  4-foot  pipe,  $13.96  per  foot ;  5-foot-pipe, 
$16.70;  6-foot  pipe,  $19.50;  /-foot  pipe,  $22.50,  etc.*  These  prices 
cover  conduit  complete,  made  with  butt-joints  and  countersunk  rivets, 
specially  well  coated,  10  per  cent  of  length  of  trench  in  rock  ledge, 
and  assumes  cost  of  steel  at  2 J  cents  per  pound. 

LITERATURE. 

CANALS    AND    MASONRY   AQUEDUCTS. 

1.  Fteley.     Stability  of  Brick  Conduits.     Jour.  Assn.  Eng.  Soc.,   1883,  n. 

P-  123. 

2.  FitzGerald.     Aqueducts  on  High  Embankments.     Eng.  News,  1884,  xi. 

p.  212. 

3.  The  New  Croton  Aqueduct  is  described  in  detail  in  the  Report  to  the 

Aqueduct  Commissioners  of  the  President,  Secretary,  and  Chief 
Engineer,  1887-95.  Also  in  Wegmann's  "  Water-supply  of  New 
York,"  1896,  and  in  various  volumes  of  the  Eng.  News  and  Eng. 
Record,  particularly  those  of  1884  and  1885. 

4.  Carter.     Farm  Pond  Aqueduct,   Boston,  Mass.  Jour.  Assn.  Eng.  Soc., 

1889,  vin.  p.  73.     Construction  through  soft  material. 

5.  Chenoweth.     The  New  York  City  Aqueduct;    its   Engeering  Features 

and  Design.     Jour.  Frank.  Inst,  1890,  cxxix.  p.  135. 

6.  The  Brooklyn  Water-works  Extension.     Eng.  News,  1891,  xxv.  p.  225. 

7.  The   Manchester  Water-works.     Engineering,   1891,  LII.   p.   435.     Also 

Proc.  Inst.  C.  E.,  1896,  cxxvi.  p.  2. 

8.  FitzGerald.     Lining  a  Water- works  Tunnel  with  Concrete.     Trans.  Am. 

Soc.  C.  E.,  1894,  xxxi.  p.  294. 

9.  Hall.     The  Santa  Ana  Canal  of  the  Bear  Valley  Irrigation  Company. 

Trans.  Am.  Soc.  C.  E.,  1895,  xxxin.  p.  61. 

10.    The  New  Croton  Aqueduct  and  Storage  System.     Eng.  Record,  1895, 
xxxii.  p.  223. 

*  Report  on  New  York's  Water-supply,  1900,  p.  328. 


628  CONDUITS  AND   PIPE-LINES. 

11.  The  Wachusett  Aqueduct  of  the  Boston  Water-works  is  fully  described 

in  the  Annual  Reports  of  the  Metropolitan  Water  Board,  1896-99. 
Detailed  descriptions  are  also  published  in  Eng.  News,  1896,  xxxv 
P-  53;  1897,  xxxvii.  p.  114;  and  in  Eng.  Record,  1898,  xxxvni 

P.  405. 

12.  Landis.     The    Croton    Aqueduct    Embankment.      Eng.    News,    189), 

xxxvni.  p.   164.     Embankments  of  old  aqueduct  illustrated. 

13.  Completing    the    Abandoned    Aqueduct    Tunnel   at   Washington,    D.C 

Eng.  News,  1899,  XLII.  p.  410. 

14.  Hutton.     The  Washington  Aqueduct,  1853-98.     Eng.  Record,  1899,  XL. 

p.  190. 

15.  Freeman.     Report  on  New  York's  Water-supply,  1900.     Contains  much 

valuable  information  on  the  construction  of  large  aqueducts. 

1 6.  Flinn.     The  Weston  Aqueduct  of  the  Metropolitan  Water-works,  Boston. 

Eng.  Record,  1902,  XLVI,  p.  362.  See  also  Eng.  News,  1901,  XLV. 
p.  360. 

17.  Report  of  the  Commission  on  Additional  Water-supply  for  the  City  of 

New  York,  1904;  contains  valuable  data  on  conduits. 

18.  Hill.     The  Torresdale  Conduit.     Relates  to  a  tunnel  used  as  an  inverted 

syphon.     Proc.  Eng.  Club,  Phila.,  April,  1905. 

19.  Schuyler.     The  New  Water-works  and  Reinforced  Concrete  Conduits  of 

the  City  of  Mexico.     Eng.  News,  1906,  LV.  p.  435. 

20.  Canal  Linings.     Bui.  No.  188,  Univ.  of  Cal.  contains  experimental  data 

on  efficiency  of  various  kinds  of  linings.  See  Eng.  News,  1907, 
LVIII.  p.  620. 


PIPE    LINES. 

1.  Herschel.     The  Works  of  the  East  Jersey  Water  Company  for  the  Supply 

of  Newark,  N.  J.     Jour.  New  Eng.  W.  W.  Assn.,  1893,  vm.  p.  18; 
Eng.  News,  1893,  xxix.  p.  559. 

2.  Schuyler.     The  Water-works  of  Denver,  Colo.     Trans.  Am.  Soc.  C.  E., 

1894,  xxxi.  p.  135. 

3.  The  New  Steel  and  Masonry  Water-supply  Conduit,  Rochester,  N.  Y. 

Eng  News,   1895,  xxxni.  p.  234;  Eng.  Record,  1895,  xxxi.  p.  346 
et  seq. 

4.  Hill.     The  Water-works  of  Syracuse.        Trans.  Am.  Soc.  C.  E.,  1895, 

xxxv.  p.  23.     30-inch  cast-iron  conduit. 

5.  Payson  Park  Reservoir,  Cambridge,  Mass.     Eng.  Record,  1895,  xxxiv. 

p.  25.     Steel  pipe-line  described. 

6.  Sixty-inch  Steel  Conduit  for  the  Water-works  of  Allegheny,  Pa.     Eng. 

News,  1895,  xxxiv.  p.  234. 

7.  Tuttle.     The   Economic   Velocity   of    Transmission   of   Water   through 

Pipes.      Eng.  Record,  1895,  xxxn.  p.  258. 

8.  Adams.     The  Astoria  City  Water-works.     Trans.  Am.  Soc.  C.  E.,  1896, 

xxxvi.  p.  i.     Steel  and  wood-stave  conduit. 

9.  Hill.     The  Thilmere  Works  for  the  Water-supply  of  Manchester.     Proc. 

Inst.  C.  E.,  1896,  cxxvi.  p.  2. 

10.    Deacon.     The  Vyrnwy  Works  for  the  Water-supply  of  Liverpool.     Proc. 
Inst.  C.  E.,  1896,  cxxvi.  p.  24. 


LITER  A  TURE.  629 

11.  Goldmark.     The  Power-plant,  Pipe-line,  and  Dam  of  the  Pioneer  Elec- 

tric   Power    Company   at   Ogden,   Utah.     Trans.    Am.    Soc.    C.   E., 
1897,  XXXVIIL  p.  246.     Steel  and  wooden  pipe-line. 

12.  The  Sewage  Farm  of  Acheres,  Paris.     Annales  des  Ponts  et  Chaussees, 

1897,  n.  p.  I.    Abstract,  Eng.  News,  1898,  xxxix.  p.  170.     Cement- 
and-steel  pipe-lines. 

13.  Bailey.     The    Design    of    Force-mains.       Eng.    Record,     1898,    xxxvu. 

P-   254. 

14.  The  Coolgardie  Pipe-line.      Eng.  News,   1898,  XL.  pp.   233,  423  ;   Eng. 

Record,  1900,  XLI.  p.  178.     A  pipe-line  328  miles  long. 

15.  Some    Notable    Australian    Steel    Pipe-lines.       Eng.  News,    1899,    XLI' 

p.  406. 

1 6.  Saville.    Pipes  and  Pipe  Laying  for  the  Metropolitan  Water-works.     Jour. 

New  Eng.  W.  W.  Assn.,  1903,  xvli,  p.  203. 

17.  The  Weston  Aqueduct  Pipe  Arch  Over  the  Sudbury  River,  Massachu- 

setts.    Eng.  Record,  1904,  XLIX.  p.  480. 

1 8.  Raymond.     The  New  Water-supply  of  Troy,  N.  Y.     Eng.  News,   1904, 

LII.  p.  300. 

19.  The  Conduit  of  the  Jersey  City  Water-supply  Co.    Of  steel  and  reinforced 

concrete.     Eng.  Record,  1904,  XLIX.  p.  38. 

20.  Butcher.     Economical  sizes  for  cast-iron  force  mains.    Eng.  Record,  1905, 

LI.  p.  558. 

21.  Anthony.     Liberation  of  Air  in  Siphons.     Trans.  Am.  Soc.  C.  E.,  1907, 

LIX.  p.  63. 

22.  Report  on  the  Proposed    226-Mile  Aqueduct   for   the  Water-supply  of 

Los    Angeles,    Cal.     Eng.  News,   1907,  LVII.  p.  93.     Eng.  Record, 
1907,  LV.  p.  107. 

23.  Allen.     A   48-in.    Riveted  Steel  Pipe  Line  at  Kansas  City,  Mo.,   Eng. 

Record,  1907,  LV.  p.  289. 

Submerged  Pipes. 
(See  also  literature  of  Chapter  XIII.) 

1.  Riffle.     A  Line  of  28-inch  Cast-iron  Submerged  Pipes  across  the  Wil- 

lamette   River    at    Portland,    Ore.     Trans.  Am.  Soc.  C.  E.,   1895, 
XXXIIL  p.  257. 

2.  Laying  Submerged  Water-mains,  Cedar  Rapids,  la.     Eng.  Record,  1898, 

xxxvii.  p.  97. 

3.  A  Submerged  Water-main    Tunnel,  Cleveland,  O.     Eng.  Record,    1898, 

xxxvin.  p.  449. 

4.  Laying  a  Submerged  Water-main  at  Cleveland,  O.     Eng.  Record,  1898, 

xxxvii.  p.  187. 

5.  Laying  Submerged  Pipes.     Eng.  Record,  1899,  XL.  pp.  72,  96. 

6.  Saville.     Submerged  Pipe  Crossings  of  the  Metropolitan  Water  Board. 

Jour.  Assn.  Eng.  Socs.,  March,  1901. 

7.  Holmes.     Submerged  Pipes.     Munic.  Eng.  Oct.,  1902. 

8.  Laying  of  6-ft.  Concrete- jacketed  Riveted  Steel  Pipes  Under  the  Hacken- 

sack  and  Passaic  Rivers.     Eng.  News,  1903,  XLIX.  p.  232. 

9.  Submerged  Pipe,  Erie  Intake.     Eng.  Record,  1905,  LII.  p.  434. 


CHAPTER    XXVI. 
PUMPING-MACHINERY. 

656.  Introductory. — The  cost  of  pumping  water  is  usually  the 
greatest  operating  expense  of  a  water-works  system,  and  a  city  which 
can  secure  an  adequate  gravity  supply  has  at  once  eliminated  a  most 
expensive  and  troublesome  feature  from  the  system.  Pipe-lines,  reser- 
voirs, dams,  and  like  structures,  if  well  designed  and  properly  con- 
structed, are  permanent  and  require  but  little  attention  and  entail  little 
expense  for  maintenance.  All  operating  mechanisms,  of  whatever 
kind,  require  more  or  less  constant  attention  and,  however  well  designed 
and  constructed,  must,  of  necessity,  be  subjected  to  more  or  less  wear 
and  possible  disarrangement  and  breakage. 

The  best  results  of  intellect  are  secured  by  concentrated  rather  than 
by  continuous  effort.  Proper  consideration  and  supervision  will  secure 
well-designed  and  well-constructed  works,  but  no  care  in  the  original 
design  or  in  the  construction  will  assu're  intelligent  operation.  In  the 
course  of  time,  intelligently  designed  works  may  come  into  the  hands 
of  unintelligent  operatives  and  poor  results  follow.  Poor  designs,  poor 
construction,  and  poor  operation  frequently  entail  large  and  unneces- 
sary expense  in  the  operation  of  pumping-plants. 

Where  water  cannot  be  obtained  at  an  elevation  sufficient  to  admit 
of  satisfactory  gravity  pressure  at  the  points  where  it  is  to  be  used, 
pumping-machinery  becomes  necessary.  It  then  becomes  the  duty  of 
the  engineer  to  design  a  pumping-plant  which  shall  be  the  most 
economical  for  the  condition  under  which  the  plant  is  to  be  established 
and  operated. 

This  design  involves  the  selection  of — 

1st.  The  best  source  of  energy  available  for  power  purposes; 

2d.  The  best  means  of  generating  such  energy  from  a  potential 
form,  and  for  converting  it  into  a  form  in  which  it  can  be  utilized  for 
power ; 

3d.  The  most  economical  means  of  transmission  of  the  power  so 
developed  from  the  point  of  generation  to  the  point  of  application ;  and 

630 


ENERGY  EXPENDED    IN  PUMPING    WATER.  631 

4th.  The  form  of  pump  best  adapted  for  the  conditions  under  which 
it  is  to  be  operated. 

These  factors  are  often  largely  modified  by  the  nature  of  the  source 
of  water-supply,  and  by  various  other  features  of  a  water-works  system. 
All  of  these  must  be  considered  in  connection  with  the  selection  of  the 
pumping-plant,  for  many  of  them  exert  an  important  influence  on  the 
conditions  under  which  the  plant  must  be  operated,  and,  therefore, 
often  determine  the  type  of  the  plant  available  for  any  particular  pur- 
pose. (See  Art.  688.) 

In  the  generation,  conversion,  transmission,  and  application  of 
power  to  pumping  purposes,  there  are  many  losses  of  energy  which  add 
greatly  to  the  expense  of  pumping.  Many  of  these  cannot  be  obviated ; 
others  can  be  removed,  or  at  least  reduced,  by  careful  design.  Care- 
ful analysis  of  each  detail  of  the  plant  will  determine  the  points  at  which 
a  saving  may  be  effected  and  will  enable  the  engineer  to  reduce  these 
losses  to  a  minimum. 

It  is  the  purpose  of  this  chapter  to  furnish  an  outline  of  the  points 
to  be  examined  in  making  such  an  investigation,  and  the  methods  to 
be  used  and  factors  to  be  considered  in  the  selection  of  pumping- 
machinery;  also,  to  describe  briefly  the  various  types  of  pumping- 
machinery  which  may  be  utilized,  and  their  adaptability  to  different 
conditions. 

657.  Energy  Expended  in  Pumping  Water.  —  An  expenditure  of 
energy  is  entailed  whenever  motion  is  transmitted  to  a  body.  A  por- 
tion of  this  energy  is  used  in  producing  the  velocity,  a  portion  in  over- 
coming frictionaf  resistances  ("lost"  work),  and  a  portion  in  over- 
coming other  resistances  involved  in  doing  "useful"  work,  such  as 
raising  a  body  to  a  higher  elevation,  etc. 

In  hydraulic  problems  the  energy  expended  in  producing  velocity 
may  be  readily  transformed  to  pressure-energy  by  the  familiar  expres- 
sion 

*•-£, 

zg 

in  which  h  =  pressure-head, 
v  =  velocity, 

g  =  acceleration  of  gravity. 

If  q  —  volume  of  water  moved,  and  w  •=.  weight  of  a  unit  of  volume, 
then  the  work  performed  in  producing  the  velocity  v  will  be 

v* 
work  =  aw —  =  awn. 


632 


P  UMPING-MA  CHINER  Y. 


pounds,  v  ~  4  feet  per  second,  the 


X  -  —  =  20.69  foot-pounds.      If    10 


Thus  if  q  =  10  gallons,   w  — 
work    will    be  equal    to    10  X 

gallons  of  water  is  moved  each  second,  then  the  rate  of  work  is  20.69 
foot-pounds  per  second  —  .37  H.P. 

The  greatest  expenditure  of  energy,  however,  is  usually  incurred 
in  overcoming  the  resistance,  or  pressure,  against  which  the  motion  is 
produced. 

If  /il  =  the  feet  in  height  to  which  water  is  raised,  then  the  useful 
work  performed  will  be:  Work  (in  foot-pounds)  =  qwhr 

If  h^  ==  IOO  feet,  q  =  10  gallons  per  second,  w  =  8J  pounds,  then 

Rate  of  work  =  qwh  =8330  foot-pounds  per  second  =  15.  14  H.P. 

Again,  if  /i2  =  the  friction-head,  the  work  lost  in  friction  will  be,  in 
foot-pounds,  equal  to  qwhy 

If  /i2  =  5,  with  q  and  w  as  above,  then  the  work  lost  to  overcome 
friction  will  equal  416.5  foot-pounds  per  second,  or  about  .75  H.P., 
and  the  total  work  done  by  the  pump  will  be 

Work  (in  foot-pounds)  =  qw(h  -f-  h^  -}-  h^. 

In  pumping  water  the  largest  expenditure  should  be  and  usually 
is  due  (except  in  the  case  of  very  long  pipe-lines)  to  overcoming 
the  resistance  of  gravity,  or  in  useful  work,  although  the  energy  used 
in  acquiring  velocity  and  in  overcoming  the  frictional  resistance  of 
passages  and  conduits  through  which  water  passes  may  be  considerable, 
especially  in  poorly  designed  machinery  or  ill-devised  pipe  systems. 

In  overcoming  gravity  or  other  resistance,  the  quantity  of  water 
raised  and  the  resistance  overcome  are  the  measures  of  energy 
expended.  In  certain  cases  the  energy  used  in  producing  velocity  may 
be  returned  in  work  done  without  loss.  In  other  cases  such  energy 
cannot  be  utilized. 

Table  No.  79  shows  the  equivalence  of  various  units  of  quantity, 

TABLE  NO.  79. 

EQUIVALENT    MEASURES    AND    WEIGHTS    OF    WATER   AT    4°    CENT.   =   39.2°  FAHR. 


U.  S.  Gallons. 

Cubic  Feet. 

Cubic  Inches. 

Imperial 
Gallons. 

Liters. 

Cubic  Meters. 

Pounds. 

I 

.13368 

231 

.83321 

3.7853 

•0037853 

8.34112 

7.48055 

I 

1728 

6.23287 

28.3161 

.0283161 

62.3961 

.004329 

.000579 

I 

.003607 

.016387 

.0000164 

.03611 

1  .2OOI7 

.  160439 

277.274 

I 

4-54303 

.0045303 

IO.OIO8 

.264179 

•035316 

61.0254 

.22012 

I 

.001 

2.20355 

264.179 

35.3T563 

61025.4 

22O.  117 

IOOO 

I 

2203.55 

.119888 

.016027 

27.694 

.099892 

•453813 

.0004538 

I 

WORK  AND   POWER  EQUIVALENTS.  633 

and     Table     No.     80     shows     the     equivalence     of    various     pressure 

TABLE    NO.  80. 

PRESSURE    EQUIVALENTS. 


Feet 
Head. 

Pounds 
per  Sq.  In. 

Pounds 
per  Sq.  Foot. 

Pounds 
per  Circular 
Inch. 

Inches  of 
Mercury, 
32°  Fahr. 

Kilograms 
per  Sq.  Centi- 
meter. 

Atmosphere. 

I 

-4335 

62.425 

.3413 

.882 

.03047 

.02945 

2.307 

I 

144 

.7854 

2.0379 

.07029 

.06794 

.01602 

.006939 

I 

•00545 

.01414 

.000487 

.  00047 

2-937 

1-273 

183.3 

I 

2-594 

.08952 

.08649 

I.I33 

.4912 

70.73 

.3858 

I 

.03453 

.03334 

32.821 

14.225 

2047  .  8 

H.I74 

28.992 

I 

.96652 

33-95 

14.72 

2119.7 

11.562 

29.921 

1-035 

I 

resistances,  which,  in  any  particular  case,  may  be  due  to  gravity  or  to 
other  causes,  such  as  the  resistance  of  the  spring  of  a  relief-valve,  or 
the  friction  through  pipe,  hose,  nozzle,  etc.  In  pumping  water  these 
two  tables  include  the  elements  of  the  useful  work  done. 

658,  Work  and  Power  Equivalents. — Work  is  a  phenomenon  of 
energy ;  it  is  the  overcoming  of  a  resistance  b}'  a  force  acting  through 
space.  Power  is  the  rate  of  work  and  involves  the  idea  offeree,  space, 
and  time. 

In  pumping  water  any  form  of  energy  may  produce  a  force  which, 
when  properly  applied,  will  overcome  a  given  resistance,  such  as  a 
given  head  or  pressure.  In  doing  this,  work  is  performed.  If  a 
definite  weight  or  quantity  of  water  is  pumped  against  a  definite  head 
or  pressure  in  a  given  time,  certain  work  is  done  each  unit  of 
time.  Thus  a  rate  of  work  is  established  and  certain  power  is 
expended.  Both  work  and  power  in  pumping  are  therefore  measured 
by  the  quantity  of  water  pumped  and  the  resistance  pumped  against. 
For  considering  power,  the  second,  minute,  hour,  or  day  are  the  units 
of  time  used. 

Table  No.  81  gives  the  equivalence  of  units  of  energy  or  work,  i.e., 
the  idea  of  time  is  not  involved. 

Besides  the  units  of  work  given  in  Table  No.  8 1  the  various  power- 
units,  when  limited  to  a  definite  time,  may  also  be  used  to  designate  a 
definite  amount  of  work,  in  which  the  unit  of  time  is  used  to  limit  the 
quantity  of  work  to  be  performed,  but  does  not  necessarily  involve  the 
idea  of  the  time  in  which  the  said  work  is  performed.  Various  fuels  and 
other  forms  of  potential  energy  may  also  be  expressed  directly  in  foot- 
pounds. Table  No.  82  shows  the  relation  or  equivalence  of  such  units 
in  foot-pounds. 


634 


PUMP  ING- MA  CHINER  Y. 
TABLE    NO.    81. 

EQUIVALENT    UNITS    OF    ENERGY. 


Work. 

Heat,  B.T.U. 

Electricity. 

Hydraulic  Energy. 

Foot- 

Degree- 

Volt- 

Foot- 

Foot- 

Pound- 

Pound- 

pounds. 

pounds. 

coulombs. 

gallons. 

cubic-feet. 

gallons. 

cubic  feet. 

I 

.001285 

.0003766 

.12 

.Ol6 

.0519 

.0069 

778 

I 

.2929 

93-28 

12.448 

40-394 

5.368 

2655-4 

3-4I4 

I 

318.39 

42.486 

137.87 

183.23 

8.341 

.OIO72 

.003140 

I 

.1334 

•433 

•05754 

62.39 

.08033 

-02353 

7.48 

I 

3.245 

.4312 

IQ.259 

.  02476 

.007255 

2.309 

.30816 

I 

.1329 

I44-92 

.18630 

•05457 

17-37 

2.318 

7.524 

I 

TABLE    NO.  82. 

WORK    EQUIVALENTS. 
Unit. 

Horse-power  hour 

Kilo-watt  hour 

Pound  of  steam  (approximate) 

British  thermal  unit 

Pound  of  carbon  (approximate) 

Pound  of  hard  coal  (approximate) 

Pound  of  soft  coal  (approximate) 

1,000,000  gallons  i  foot  high  (water) 

1000  gallons  100  feet  high  (water) 

100  cubic  feet  I  foot  high  (water) 


Equivz 


lent  in  Foot-pounds. 
1,980,000 
2,654,150 
778,000 

778 

11,500,000 

11,400,000 

9,910,000 

8,341,000 

834,100 

62,396 


In  many  problems  of  pumping,  questions  of  power,  rather  than 
work,  are  involved.  That  is,  a  definite  rate  of  pumping  must  be  con- 
sidered. Table  No.  83  gives  the  equivalence  of  common  power  units 
used  for  such  problems. 

TABLE    NO.  83. 

EQUIVALENT    UNITS    OF    POWER. 


Work. 

Heat. 

Electricity. 

Water-power. 

Foot-lbs. 
per  Minute. 

Horse- 
power. 

Thermal 
Units 
per  Minute, 
B.T.U. 

Watts. 

Foot- 
gallons 
per  Minute. 

Foot- 
cubic-feet 
per  Minute. 

Pound- 
gallons, 
per  Minute, 

Pound 
cubic-feet, 
per  Minute. 

I 

.  0000303 

.001285 

.O226 

•  12 

.016 

.0519 

.0069 

33,000 

I 

42.416 

746 

3960 

528 

I7I3.4 

229.05 

778 

•02357 

I 

I7-58 

93.28 

12.444 

40.394 

5.388 

44.24 

.00134 

.0568 

I 

5.308 

.70895 

2.296 

•307 

8-34 

.00025 

.OIO7 

.18856 

I 

•1337 

•433 

•0579 

62.396 

.00189 

.  0802 

I.4I05 

7.48 

I 

3-24 

•433 

19.26 

.00058 

.0247 

.435 

2.31 

•309 

i 

.1337 

144-92 

.  00436 

.1851 

.0326 

17-37 

2.31 

7.48 

i 

SOURCES   OF  POTENTIAL   ENERGY.  635 

659.  Classification  of  Energy  Losses. — If  it  were  possible  to  perform 
work  or  to  utilize  power  without  loss,  the  amount  of  energy  which 
would  be  necessary  to  raise  any  given  quantity  of  water  in  any  given 
case  could  be  ascertained  from  the  preceding  tables.  Energy  loss  is, 
however,  concomitant  with  the  use  of  all  machinery,  and  differs  with 
the  class  and  complication  of  the  machinery  through  or  in  which  the 
energy  is  generated,  transformed,  transmitted,  and  utilized. 

In  general  the  operation  of  applying  energy  to  pumping  water  con- 
sists of  the  generation  of  energy  from  a  potential  source,  the  conversion 

TABLE  NO.  84. 

CLASSIFICATION    OF    ENERGY    LOSSES    IN    PUMPING. 

Losses. 
|-Internalg-cornbustion  engine.  |  Eng-ne  ^^ 

I  Fuel -j  (  Furnace. 

fc   j  I  Steam •<  Boiler. 

(  Piping. 
Direct  (ram) Ram  losses. 


-direct  (Whee,s) 


'     Various    mechanical    and 
Minor  sources  ........     Waves  (motors).  f     other      losses     due    to 

i.  Sun  heat  (solar  engines).       j      -""hod  used. 
Internal-combustion  Engine  .......................      Included  in  engine  losses. 

c.  (  Engine  and    connection 

................................  •(      losses. 

Electrical  .......................................      Dynamo  losses. 

Hydraulic  .......................................      Pump  losses. 

Pneumatic  ......................................      Compressor  losses. 


Hydraulic, 


Electrical. 


Pipe  friction. 
Motor  losses. 
Connections. 
Transformer  losses. 
Wire  losses. 
Motor  losses. 


PH 


f 


Connections, 
f  Pipe  friction. 

P-**.rr M^oHosfe, 

[Connections. 
(  Influx. 

Inlet-pipe -|  Velocity. 

Friction. 

Pumping \  (Friction    in     valves     and 

Pump •<       water  passages. 

(  Mechanical  friction. 

(.Discharge-pipe Pipe  friction. 

Ram Pipe  losses. 

(  Radiation. 

Steam -|  Condensation. 

(  Pipe  losses. 
Air Air-pipe  losses. 


636 


P  UMPING-MA  CHINER  Y. 


of  such  energy  into  a  kinetic  form,  its  transmission  to  the  location  of 
the  pump,  and  its  application  to  pumping  the  water  by  means  of  the 
pumping  machinery  used. 

The  economical  application  of  pumping-machinery  depends  on  the 
reduction  of  all  energy  losses  to  the  lowest  practical  amount.  These 
losses  should  always  be  examined  in  detail,  and  in  order  that  they  shall 
in  no  case  be  overlooked  it  is  well  to  examine  the  losses  under  the 
following  heads : 

Generation  Losses. 
Conversion  Losses. 
Transmission  Losses. 
Application  Losses. 

These  principal  divisions  should  be  further  subdivided  for  detailed 
consideration  as  shown  in  Table  No.  84,  the  items  of  which  will  next 
be  considered. 

SOURCES    OF    POTENTIAL    ENERGY. 

660.  Available  Sources. — The  sources  of  potential  energy  available 
for  power  purposes  are  fuel,  water-power,  wind,  solar  energy,  and 
chemical  energy  (which  properly  also  includes  the  energy  of  fuel  which 
is  rendered  kinetic  through  chemical  union).  Fuel  is  most  generally 
utilized  by  means  of  heat  and  heat-engines,  water-power  by  means  of 
various  forms  of  water-motors,  the  wind  by  means  of  windmills, 


TABLE  NO.  85. 

FUELS  :    CALORIFIC    VALUE   AND    EQUIVALENTS. 


Fuel. 

Average  Heat-units. 

Equivalent 
Evaporation 
from  and  at 
212°  Fahr; 
Pounds. 

Equivalent 
Horse-power 
Hours. 

Equivalent 
Million 
Foot-gallons. 

Per  Pound. 

Per  1000 
Cubic  Feet. 

Equivalents  for  Calculations 
Coke  

IO.OOO 
14,880 
14,660 
12,740 
7,740 
19.150 

10.35 
15-40 
15.17 
13.18 
8.01 
19.82 
917-06 

599  93 
262.00 
115.10 
103.50 

3.87 
5-84 
5.76 
5-00 
3-04 
7.52 
348.08 
224-32 
99.45 
43-69 
38.90 

-921 
1.384 

I-365 

1.185 
.720 
1.782 
82.494 
53-I64 
23.569 

10-354 
9.219 



Wood 

885,880 
570,900 
253,100 
Ill.igo 
100,000 

Equivalents  for  Calculations 

*  Gasoline,  the  form  of  petroleum  used  in  the  gasoline  engine,  weighs  about  5.8 
Ibs.  to  the  gallon.      Each  gallon  contains  about  110,000  B.  T.  U. 


GENERATION  AND    CONVERSION   OF    ENERGY.  6$? 

chemical  energy  by  means  of  electric  batteries,  and  solar  energy  by 
means  of  solar  engines.  In  a  commercial  way,  fuel  and  water-power 
only  are  of  great  importance  or  need  to  be  here  considered. 

661.  Fuel. — Fuel  is  the  source  of  potential  energy  most  widely  used 
commercially.      From  wood,  coal,   petroleum,   natural  gas,  and  other 
fuels,  energy  is  developed  in  the  form  of  heat  by  combustion. 

The  average  value  of  various  fuels  is  approximately  as  shown  in 
Table  No.  85. 

662.  Water-power. — Water-power    is    readily  convertible    by    easy 
calculations  into  water  pumped.      Without  loss,   I  foot-pound   ofwaler 
for  power  purposes  should  give    I    foot-pound  of  water  pumped.      For 
example,    10  pounds  of  water  falling   10  feet   possess    100  pounds  of 
energy  and  would,  if  utilized  without  loss,  raise  I    pound  of  water  100 
feet,  2  pounds  50  feet,  4  pounds  25  feet,  etc. 

If  utilized  without  loss,  we  have  said ;  but  it  has  already  been  stated 
that  utilization  of  energy  without  loss  is  impossible,  hence  the  above 
proportions  of  work  done  are  in  practice  materially  reduced. 

GENERATION   AND    CONVERSION    OF    ENF.RGY. 

663.  Ordinary  Efficiency  of  Generators  and  Motors. — The  proportion 
of  energy  which  can  be  realized  in   useful  work  will  depend  on  the 
efficiency  of  the  machines  by  means  of  which  energy  is  being  utilized. 
By  efficiency  is  meant  the  ratio  of  energy  utilized  in  useful  work  done 
to  energy  applied  for  power  purposes. 

Any  prime  mover  may  be  utilized  by  proper  connection  with  a  suit- 
able pump  for  the  purpose  of  pumping  water.  The  loss  of  energy  in 
any  case  will  depend  both  on  the  type  of  machine  used  and  the  design, 
construction,  and  operation  of  the  particular  machine  in  question. 
The  results  usually  attained  in  good  practice  with  various  generators 
and  motors  which  may  be  utilized  for  pumping  are  shown  in  Table 
No.  86. 

664.  The  Steam-boiler. — Fuel  energy  is  most  commonly  converted 
into  a  form  in  which  it  can  be  applied  for  power  purposes  by  means  of 
the  steam-boiler,  although  the  internal-combustion  engine  has  also  now 
become  an  important  factor  for  power  installations. 

On  account  of  heat  lost  in  the  waste  gases  from  the  boiler-furnace, 
only  about  83  per  cent  of  the  calorific  value  of  the  fuel  can  theoretically 
be  made  available  without  the  use  of  economizers  and  forced  draft. 
The  best  boilers  will  utilize  about  90  per  cent  of  this  available  energy, 
or  about  75  per  cent  of  the  full  calorific  power  of  the  fuel  used. 


638 


P  UMPING-MA  CHINER  Y. 
TABLE   NO.   86. 

ORDINARY    EFFICIENCIES    OF    GENERATORS   AND    MOTORS. 


Type  of  Machine. 


Water-wheels: 

Overshot  wheels 65 

Breast  wheel 60 

Undershot  wheel 25 

Turbines 60 

Impulse- wheel 75 

Steam  generators:    Boilers 50 

Steam-engines: 

("Triple-expansion  Corliss 15 

~       ,        .                1  Compound  Corliss 12 

Condensing. . . .  -j  Simp*Je  Corliss JO 

[^  Compound  high-speed  .......  10 

f  Compound  Corliss TO 

|  Simple  Corliss 7 

Non-condensing«(  Compound  high-speed 7 

!  Simple  high-speed 6 

(.  Simple  slide-valve 5 

Heat  engines: 

Gas-  or  oil-engines 16 

Diesel  motor 25 

Steam  air-compressors: 

Compound  condensing  Corliss 10 

Simple  condensing  Corliss 7 

Simple  Corliss 5 

High-pressure 3 

Small  straight-line 2 

Electrical  machinery  : 

Dynamos 80 

Motor  (large) 80 

Motor  (small) 75 

Transformer 50 


Ordinary  Efficiency  at 
Full  Load.    ' 


Minimum.      Maximum 


75 
65 
40 

85 
85 
75 

18 
15 

12 

12 

12 

9 

9 
7 

7 

20 
30 

12 

9 
6 

4-5 
3 

92 
90 

85 
95 


The  greatest  care  is  necessary  in  the  design  and  construction  of 
furnace,  boiler,  and  accessories  in  order  to  develop  the  maximum 
efficiency  and  secure  the  most  economical  results  in  the  utilization  of 
fuels.  Radiation  and  condensation  are  important  factors  in  boiler 
losses  and  should  be  rendered  as  small  as  possible  by  properly  protect- 
ing the  boiler.  The  same  losses  are  also  important  in  the  steam-pipes 
which  transmit  the  steam  from  generator  to  motor  and  must  be  kept  at 
a  minimum  by  proper  precautions. 

665.  The  Steam-engine. — Of  the  energy  delivered  to  the  engine,  the 
proportion  actually  utilized  depends  upon  the  character  of  the  engine 
used,  its  design,  and  the  condition  in  which  it  is  maintained. 

A  perfect  engine,  on  account  of  the  nature  of  steam,  could  utilize 
only  about  25  per  cent  of  the  energy  of  the  steam  delivered  to  it.  In 


THE   STEAM-ENGINE. 


639 


actual  practice,  however,  the  best  engines  utilize  only  about  17  per 
cent,  and  poor  engines  in  poor  condition  frequently  utilize  less  than 
I  per  cent  of  the  energy  of  the  steam. 

If  the  steam-consumption  per  actual  horse-power  per  hour  for  any 
engine  is  known,  the  efficiency  of  the  engine  can  be  readily  determined 
from  Table  No.  82. 

666.  Use  of  Steam  Expansively. — In  the  simplest  form  of  steam- 
engines  and  of  steam-pumps,  the  steam  at  full  pressure  follows  the 
piston  for  the  full  length  of  every  stroke  and  the  expansive  force  of  the 
steam  is  not  utilized.  This  is  the  case  in  direct-acting,  reciprocating, 
high-pressure  steam-pumps.  In  higher  types  of  steam-pumps  and  in 
almost  all  types  of  steam-engines  the  steam  is  cut  off  after  a  portion  of 
the  stroke  is  completed,  and  the  steam  is  allowed  to  expand  for  the 
balance  of  the  stroke. 

In  Fig.   I//  let  ab  represent  the  pressure  on  the  steam-piston,  and 


ol' 


a!" 

FIG    177. 


aa'  the  space  passed  through  by  the  piston ;  then  their  product,  repre- 
sented by  area  abb' a' ,  equals  the  work  done  by  a  unit  of  steam  with 
pressure  ab,  and  which  follows  the  piston  for  a  space  aa' .  Now  if.  at 
ab'  the  steam-supply  is  cut  off  and  the  piston  still  advances  to  position 
a'b"  or  a"!b'" ,  etc.,  the  expansive  force  of  the  steam  will  still  cause  a 
pressure  to  be  exerted  against  the  piston  which  will  decrease  in  amount 
as  the  piston  advances,  but  which  is  nevertheless  adding  constantly 
to  the  work  done,  as  shown  by  the  area  which  represents  in  the 
diagram  the  work  of  a  unit  of  steam.  This  additional  work  is  obtained, 
it  should  be  noted,  with  no  additional  expenditure  of  steam.  The 


640 


P  UMPING-MA  CHINER  Y. 


additional  work  done  by  each  steam-unit  depends  on  the  degree  of 
expansion  obtained,  which  in  turns  depends  on  the  type  of  engine  or 
pump  used,  and  various  other  considerations  which  cannot  be  discussed 
here. 

From  Fig.  177  it  is  seen  that  if  the  steam  is  allowed  to  expand  and 
the  pistons  to  increase  its  stroke,  the  power  obtained  will  be  increased. 
The  power  obtained  from  a  cylinder  of  given  size  will,  however,  be 
greater  when  the  steam  is  carried  for  the  full  length  of  the  stroke. 

When  the  steam-supply  is  cut  off  at  a  fraction  of  the  stroke  and 
allowed  to  expand  for  the  remainder  of  the  distance,  the  average  or 
mean  effective  pressure  (M.E.P.)  decreases  and  the  horse-power  of  the 
engine  will  likewise  decrease  unless  the  pressure  of  the  steam  is 
increased  sufficiently  to  offset  the  loss  in  M.E.P.  thus  occasioned.  In 
.Table  No.  87  is  shown  the  initial  pressure  (column  3)  needed  to  main- 
tain a  M.E.P.  of  75  pounds,  or,  in  other  words,  the  necessary  initial 
pressure  needed  with  various  cut-offs  to  obtain  the  same  horse-power 
from  the  same  size  steam-cylinder. 

TABLE  NO.  87. 

ECONOMY    SECURED    BY    USING    STEAM    EXPANSIVELY. 


Point  of 
Cut-off. 

Boiler-pressure  required  to  give  Same 
Power  of  Engine. 

Per  Cent  of 
Saving  in 
Fuel. 

When  Used 

When  Cut 

Ratio. 

Full  Stroke. 

Off. 

I 

75 

75 

0 

i 

75 

76 

.01 

12 

i 

75 

77 

•03 

22 

i 

75 

82 

.09 

32 

\ 

75 

88.5 

.18 

41 

i 

75 

99 

•32 

50 

* 

75 

125-5 

.67 

58 

i 

75 

195 

2.60 

68 

From  this  it  is  seen  that  high  rates  of  expansion  require  either  high 
initial  steam-pressure  or  large  engines.  And  the  limit  is  soon  reached 
at  which  the  economy  of  a  greater  degree  of  expansion  is  offset  by  the 
extra  cost  of  the  engine  necessary  to  obtain  it.  Cylinder  condensation 
and  various  questions  of  construction  also  enter  into  the  question  and 
become  important  factors. 

The  relative  theoretical  saving  effected  by  different  degrees  of 
expansion  are  shown  in  the  fifth  column  of  Table  No.  87. 

667.  Use  of  Condensers. — If  the  steam,  after  being  used  in  the 
engine  or  pump-cylinder,  is  exhausted  into  the  atmosphere,  the  piston 


THE   STEAM-ENGINE. 


641 


will  work  against  a  back  pressure  equal  to  atmospheric  pressure  (about 
14.7  pounds)  plus  the  friction  in  exhaust-passages  (usually  from  2  to  3 
pounds).  If  the  exhaust  passes  into  a  condenser,  the  back  pressure  is 
relieved  in  proportion  to  the  vacuum  carried. 

Usually  a  condenser  will  add  about  10  pounds  to  the  mean  effective 
pressure  in  the  engine-cylinder.  The  percentage  of  saving  by  it  will 
be  the  ratio  of  pressure  added  to  mean  effective  pressure  which  would 
otherwise  be  developed  in  the  cylinder,  or 

j^g-p-    =  percentage  saved. 

Dr.    C.    E.    Emery*  gives   Table   No.  88,  showing   the   estimated 

TABLE    NO.   88. 

PERCENTAGE    OF    GAIN    BY    USE    OF    CONDENSER. 


Type  of  Engine. 

Pounds  Steam  per  Indicated  H.P.  per  Hour. 

Per  Cent 
Gained. 

Non-condensing. 

Condensing. 

Probable 
Limits. 

Assumed  for 
Comparison. 

Probable 
Limits. 

Assumed  for 
Comparison. 

35  to  26 
32  to  24 

30  to  22 
27  to  21 

25  to  19 
24  to  18 
24  to  16 
23  to  14 

22 
20 
20 
17 

33 
31 
23 
29 

29 
26 
24 

steam  consumption  of  various  engines  and  the  saving  effected  by  the 
use  of  condensers. 

668.  Average  Steam  Consumption. — The  approximate  average 
steam  consumption  per  indicated  horse-power  for  various  classes  of 
engines  is  shown  in  Table  No.  89. 

TABLE    NO.    89. 

APPROXIMATE  STEAM    CONSUMPTION    PER    I. H.P.  OF  VARIOUS    TYPES    OF    STEAM-ENGINES. 
Pound  of  Steam  per  Indicated  Horse-power  per  Hcur  at  Full  Load. 

Triple-expansion  condensing  Corliss 12  to  14  pounds. 

Compound  condensing  Corliss 14  to  18  " 

Simple  condensing  Corliss 18  to  21  " 

Compound  Corliss 18  to  21  " 

Compound  condensing  automatic 20  to  24  " 

Simple  Corliss 24  to  30  " 

Simple  high-speed 301036  " 

Simple  slide-valve 33  to  45  " 

*  Trans.  Am.  Inst.  E.  E.,  March,  1893. 


642 


PUMPING-MA  CHINER  Y. 


669.  Effect  of  Operating  at  Partial  Load. — From  6  to  15  per  cent 
of  the  indicated  horse-power  of  an  engine  is  lost  in  friction  in  well- 
designed  engines  at  full  load.  At  partial  load  the  percentage  of  loss 
is  much  greater. 

All  machinery  gives  its  greatest  efficiency  when  operated  at  or  near 
its  maximum  capacity.  This  is  due  to  the  fact  that  the  friction  of  most 
machinery  is  practically  constant  at  all  loads,  or  nearly  so.  With  a 
I  oo  horse-power  engine  the  friction  of  the  engine  will  be  perhaps  about 
10  horse-power,  hence  the  following  condition  will  result: 


Useful  Load.  Friction  Load. 

With  no  load 10  H.P. 

With  10  H.P 10  H.P. 

With  30  H.P 10  H.P. 

With  70  H.P 10  H.P. 

With  100  H.P.  .  10  H.P. 


PROBABLE:  STEAM  CONSUMPTION  PER. 

DELIVEBtD   nOfc§E    POWER.. 


Mechanical 
Efficiency. 

Of0 


CURVE..N?!.  NON-CONDENSING.  SIMPLE.  THR.OTTUNG.     STEAM    SO  POUNDS* 


t  MON-  CONDENSING.  AUTOM/VTIC 

5.  NON- CONDENSING,  COMPOUND  AUTOMATIC 

4. CONDENSING,  CORLISS 

51  CONDENSING.  COMPOUND  AUTOMATIC. 

e.  CONDENSING,  COMPOUND  CORLISS. 

7.  CONDENSING,  TRIPLE.    EXPANSION. 


100  <> 

100  it 

80  .1 

\zs  » 

IOO  n 

ISO  u 


.£5  .50  35  1.0  T.Z5  1.50 

PROPORTION   THAT  ACTUAL  LOAD   3£APJ^  TO  ieATE.D  POWEP.. 
FIG.  178.— STEAM  CONSUMPTION  FOR  VARIOUS  CLASSES  OF  ENGINES. 

The  steam  consumption  of  various  classes  of  engines  at  various 
loads  is  well  illustrated  by  the  diagram  of  Fig.  178,  modified  slightly 
from  a  table  by  Prof.  R.  C.  Carpenter. 


HE  A  T-ENGINES. 


643 


670.  Heat-engines. — Only  about  12  per  cent  of  the  fuel  energy  is 
utilized  in  the  indicated  horse-power  of  the  best  steam-engines,  while 
in  ordinary  practice  only  from  I  to  3  per  cent  is  so  utilized.  As  the 
loss  is  largely  due  to  the  nature  of  steam,  it  has  resulted  in  attracting 
the  attention  of  inventors  to  other  forms  of  heat-engines  for  power  pur- 
poses. The  best-known  forms  of  these  are  the  various  gas-  and 
gasoline-engines  in  which  a  mixture  of  air  and  gas  or  vapor  is  ignited 
or  exploded  in  the  engine-cylinder  itself,  without  the  interposition  of  a 
boiler.  These  engines  utilize  from  16  to  20  per  cent  of  the  calorific 
value  of  the  fuel  used,  and  in  some  special  forms  30  per  cent  has  been 
utilized.  These  engines  are  also  available  for  power  without  the  slow 
process  of  getting  up  steam,  an  important  matter  in  operating  pump- 
ing-plants  for  fire  service.  Another  favorable  condition  is  the  small 
amount  of  attention  necessary  in  their  operation. 

The  availability  of  this  class  of  motors  in  entirely  a  matter  of  con- 
dition, which  may  be  adverse  or  favorable  in  any  locality  or  for  any 


FIG.  179. — GASOLINE  PUMPING-PLANT,  DUNDEE,  ILLINOIS. 


purpose.       Fig.     179   shows   one  of  two  gasoline-engines  with  direct- 
connected  pumps  installed  in  the  water-works  at  Dundee,  111. 

While  these  engines  require  but  comparatively  little  attention,  they 
must  have  such  attention,  and  the  expense  of  this  must  not  be  under- 
estimated. Where  other  work  can  be  done  by  the  engineer,  only  a 
portion  of  his  time  need  be  charged  to  the  operation  of  the  plant,  but 
where  no  such  work  is  possible  his  entire  time  must  be  considered. 


644  P  UMPING-  MA  CHINER  Y. 

The  average  amount  of  fuel  required  by  these  engines  at  full  load  is 
about  as  follows: 

Gas-engines  :    1  2  to  i  5  cu.ft.  of  natural  gas  per  actual  H.P.  per  hour. 

1  8  to  22  cu.  ft.  of  coal-gas  per  actual  H.P.  per  hour. 

Gasoline-engines:    .11  to  .14  gal.  of  gasoline  per  actual  H.P.  per  hour. 

The  makers  of  high-grade  gas-engines  will  guarantee  to  develop 

an  actual  horse-power  hour  on  12,600  B.T.U. 

TRANSMISSION    OF    ENERGY. 

Having  developed  the  power  at  the  shaft  of  the  engine  or  water- 
wheel,  it  must  next  be  transmitted  to  the  pump.  This  operation  also 
involves  some  waste  of  energy. 

671.  Methods  of  Transmission  and  Approximate  Efficiencies.  —  Direct 
Connection.  —  When  the  machine  to  which  transfer  is  made  is  connected 
directly  to  the  motor  without  interposition  of  extra  boxes  or  gearing 
and  with  shafting  directly  in  line,  no  extra  friction  is  involved  and  no 
loss  is  sustained.  (See  Figs.  179  and  180.) 

Shafting.  —  Where  a  long  shaft  is  directly  connected  to  the  source 
of  power  without  gearing,  the  loss  is  in  proportion  to  the  number  of 
bearings,  their  lubrication,  arrangement,  and  alignment.  In  shop 
systems  the  losses,  including  belt  and  shaft  systems,  are  often  from  I  5 
to  50  per  cent  with  full  loads,  and  are  much  greater  proportionally  for 
light  loads. 

Gearing.  —  Bevel-gearing,  used  to  turn  a  right  angle  with  shafting, 
frequently  uses  from  15  to  25  per  cent  of  power  transmitted,  even 
where  cut  gears  are  used. 

In  gear-trains  or  worm-gearing,  40  per  cent  of  the  power,  or  more, 
may  be  consumed,  according  to  the  construction  and  complication. 

Belts.  —  The  loss  in  simple  belts  is  usually  from  5  to  15  per  cent; 
tight  belts  cause  excessive  friction  in  bearings  and  consequently  large 
losses. 

Rope  Gearing.  —  With  the  American  system  of  rope  transmission 
the  loss  is  less  than  with  belts,  and  in  single  transmission  will  vary  from 
3  to  10  per  cent.  (See  Fig.  62,  page  316.) 

Wire-rope  Gearing  —  Unwin  gives  the  efficiency  of  wire-rope  gear- 
ing at  full  load  from  Zeigler's  experiments  as  follows: 


Efficiency  =  -96/v    '    ', 

t 
for  M  intermediate  and  two  terminal  stations. 


FIG.  180. — ELECTRIC  PUMPING-PLANT,  DEKALB,  ILLINOIS. 
Front  View. 


FIG.  180. —ELECTRIC  PUMPING-PLANT,  DEKALB,  ILLINOIS. 
Rear  View. 


CLASSIFICATION  OF  PUMPS. 


649 


Pneumatic  Transmission. — Friction  losses  are  from  3  to  8  per  cent 
per  mile.  The  efficiency  of  motors  varies  from  40  per  cent,  when  air 
is  used  cold,  to  as  high  as  70  per  cent,  when  the  air  is  reheated  before 
use. 

Hydraulic  Transmission. — This  method  of  transmission  can  be 
calculated  from  friction  tables,  and  the  efficiencies  of  the  class  of  pumps 
used  as  given  herein. 

Electrical  Transmission. — The  efficiencies  of  electrical  transmission 
can  be  calculated  from  the  efficiencies  of  the  electrical  machinery, 
together  with  the  line  and  transformer  losses,  which  in  good  practice 
is  not  more  than  from  5  to  10  per  cent. 

THE    PUMP   IN    GENERAL. 

672.  Classification  of  Pumps. — The  function  of  all  pumping-ma- 
chinery  for  water-works  purposes  is  to  take  water  from  some  given 
source  and  move  it  to  a  new  position. 

TABLE    NO.    90. 

CLASSIFICATION    OF    PUMPS. 


r  1   I 

Action.  .  .  . 

j  Double. 

\  Single. 

Class  

j  Piston.       (  Inside-packed. 

\  Plunger.  \  Outside-packed. 

(  Center-packed. 

\  Single. 

•d 

Power.  .  .  •<  Duplex. 

o 

•S 

(  Triplex. 

,•  ^ 
§'•3 

Recipro-^ 
eating. 

/ 
Tvoe.  . 

Application.  .  .  j 

Direct-acting. 

"\  Steam.                                        I 

gg. 

|  Arrangement,  -v 

Crank  &  fly-wheeL 

r^ 

L                     ( 

Compensator. 

E  > 

Hydraulic.   •]  ^irect"actin&- 

C/5 

^  L>TcinK  and  fly* 

wiieei* 

5^ 

Arrangement,   j  Tjer.lca  *    . 

1 

1         .£ 

Use   

j  Surface  (suction). 

(  Submerged  or  deep  well. 

Rotary. 

Air-displacement.     c  ~ 

r*                                                   \    oCrCW. 

Steam-vacuum.             <-i._:_ 

Continuous-flow.  .  .  \ 

V^lldlU. 

1 

U  pump. 

I                           L 

Double-acting. 

f 

f  T                                 (  One 
Impeller  1  pj 

ed. 

IMPELLER.               Cent 
Continuous    applica- 

rif ugal.  .  .  i  Case  1  ?,ide 

suction, 
ble  suction. 

Y                                 1  Dou 

tion  through  some  • 
mechanical  agency 

Arrrangement.   -j  y 

izontal. 

or  medium. 

(  Water. 

Tet 

....-{  Steam 

f 

(Air. 

IMPULSE  (as  name  implies)  . 

Water-1 

*am. 

BUCKET  (receptacle  alternately  filled  and  emptied)..  •!  Bane^  ' 

650  P  UMPING-MA  CHINER  Y. 

Pumps  may  be  classified  in  various  ways,  but  for  the  consideration 
of  their  mechanical  action  they  may  be  best  considered  under  the  fol- 
lowing heads: 

1.  Displacement-pumps. 

2.  Impeller-pumps. 

3.  Impulse-pumps. 

4.  Bucket-pumps. 

The  various  subdivisions  of  the  classification  are  shown  in  Table 
No.  90. 

( I )  Displacement- pump s . 

673.  Displacement-pumps  are  those  in  which  the  volume  of  water 
raised  is  forced  from  the  pump-chamber  by  absolute  displacement  by 
some  mechanical  agency. 

674.  Reciprocating-pumps. — Of  displacement-pumps    the    ordinary 
reciprocating-pump  is  the  most  common  and  well-known  variety.      In 
reciprocating-pumps    a    piston    or    plunger   (which    is    the    displacing 
agency)  reciprocates  in  a  closed  cylinder  provided  with  the  necessary 
inlet-   and   outlet- valves,   and  alternately  inspires  and  discharges  the 
water  from  the  cylinder.      Such  pumps  are  single-acting  when  one  end 
of  the  plunger  only  acts  on  the  fluid  column  (Figs.  i8i(^)  and  187),  and 
are  double-acting  when  the  cylinder  is  so  constructed  that  the  pump 
will  act  on  both  the  forward  and  the  return  stroke  (Figs.   i8i(£),   183, 
184,  and  1 86).      Piston-pumps  are  those  in  which  a  finished  cylinder  is 
tightly  fitted  by  a  reciprocating-piston  (Figs.   181(0)  and  183). 

Plunger-pumps  are  those  in  which  the  reciprocating  part  is  a  solid 
plunger  which  does  not  come  in  contact  with  the  cylinder-walls. 
These  plungers  alternately  enter  and  withdraw  from  the  cylinder 
through  packing-glands(Figs.  iSi(£),  184,  1 86,  and  187).  The  methods 
of  packing  plunger-pumps  divide  them  into  the  additional  classes  of 
inside  (Figs.  184  and  186),  outside  (Fig.  187),  and  outside  center- 
packed  (Fig.  1 8  !'(£))  plunger-pumps.  The  differential  plunger-pump 
(Fig.  1 8 1  (<:)),  while  it  inspires  only  on  the  upward  stroke,  is,  on  account 
of  the  design  of  the  plunger,  double-acting  on  the  discharge. 

Fig.  i8i(</)  shows  a  reciprocating  piston-pump  called  a  U  pump,  in 
which  the  valves  are  placed  in  the  piston  and  the  flow  is  in  one  direc- 
tion, with  no  reversing  of  the  current  of  water.  The  most  serious 
defect  in  most  reciprocating-pumps  is  the  reversal  of  the  current,  which 
is  here  eliminated.  These  reversals  may  cause  a  considerable  loss  of 
energy  and  produce  violent  and  injurious  shock's ;  and  on  account  of 
this  defect  the  number  of  reversals  of  most  reciprocating-pumps  must 


D  ISP  LA  CEMENT-P  UMPS. 


65I 


(a)  Single-acting  Piston-pump. 


x<r)  Differential  Plunger-pump* 


Outside  Center-packed  Double-acting 
Plunger-pump. 


(e)  Rotary  Pump.  (/)  Centrifugal  Pump. 

FIG.  181. — TYPES  OF  PUMFS. 


652 


P  UMPING-MA  CHINER  Y. 


(a)  Jet-pump. 


(&)  Hydraulic  Ram. 


(e)  Air  Displacement-pump. 


(e)  Vacuum-pump. 
FIG.  182. — TYPES  OF  PUMPS. 


D  ISP  LA  CEMEN  T-P  UMPS.  653 

be  limited.  It  is  therefore  possible  to  run  pumps  of  long  stroke  at  a 
higher  piston-speed  than  those  of  short  stroke.  The  ordinary  recip- 
rocating-pump  of  10-  or  12- inch  stroke  and  limited  valve-area  should 
seldom  be  operated  at  a  greater  rate  of  speed  than  100  feet  per  minute, 
while  pumps  of  long  stroke  and  ample  valve-area  are  sometimes 
operated  at  300  to  400  feet  of  piston-travel  per  minute. 

There  is  no  such  limit  necessary  with  pumps  of  the  type  shown  in 
Fig.  181  (d\  and  hence  these  pumps  may  be  operated  at  much  higher 
speeds.  The  speed  in  this  case  is  limited  by  the  necessity  of  limiting 
the  velocity  of  the  water  in  its  passage  through  the  valves. 

In  Figs.  181  (a),  (£),  (<:),  and  (d)  the  water  end  only  of  the  pump 
is  shown.  The  piston-  or  plunger-rods  may  be  operated  by  a  connect- 
ing-rod and  crank  to  which  power  is  furnished  by  any  form  of  motor, 
or  a  second  cylinder  may  be  attached  to  the  other  end  of  this  rod  and 
the  water  end  operated  by  hydraulic  or  steam  power  directly.  The 
arrangement  of  the  pump  for  the  application  of  power  gives  rise  to  the 
additional  classification  of  reciprocating-pumps  into  power  (Figs.  179 
and  1 80),  steam  (Figs.  183-187),  and  hydraulic  pumps.  Power- 
pumps  include  all  that  class  of  pumps  which  require  an  independent 
motor  for  their  operation.  The  term  ' '  power-pump, ' '  however, 
includes  all  other  forms  of  pumps  besides  the  reciprocating  variety, 
which  are  operated  by  independent  motors.  Reciprocating  power- 
pumps  may  be  Single-cylinder,  Duplex,  or  Triplex,  in  accordance  with 
the  number  of  cylinders  of  which  the  pump  is  composed. 

675.  The  Steam-pump. — The  steam-engine  can  be  applied,  in 
common  with  other  motors,  to  the  operation  of  power-pumps ;  and 
such  an  arrangement  when  properly  made  is  highly  efficient  and  worthy 
of  careful  investigation  and  consideration.  Such  an  arrangement 
involves  the  use  of  two  separate  machines.  In  a  large  and  important 
class  of  pumping-machinery  the  steam-  and  water-cylinders  are  placed 
in  the  same  machine  and  in  such  cases  are  best  considered  together. 
Such  pumps  are  called  "Steam-pumps." 

Numerous  varieties  of  this  class  of  pumps  are  in  use.  From  the 
methods  of  application  of  steam  this  class  of  pumps  is  divided  into 
"high-pressure"  steam-pumps,  which  include  all  those  in  which  the 
steam  is  used  at  its  initial  pressure  for  the  full  length  of  the  stroke  in  the 
cylinder  and  not  again  used,  and  "  compound  "  steam-pumps,  in  which 
the  steam  is  used  expansively  in  two  or  more  cylinders.  The  arrange- 
ment and  design  of  the  pump  give  rise  to  other  divisions.  In  the  direct- 
acting  pump  the  steam-piston  is  connected  directly  by  means  of  a 
piston-rod  with  the  pump-piston  or  plunger,  the  piston-rod  being  com- 


654 


P  UMPING-MA  CHINER  Y. 


mon  to  both  steam-piston  and  water-plunger  (Figs.  183  and  184).  In 
steam-pumping  machinery  of  this  class  having  only  one  set  of  steam- 
cylinders  the  steam  must  be  used  at  its  initial  pressure  for  the  full  length 
of  the  stroke,  as  in  the  simple  form  of  this  pump  (Fig.  183)  there  are 
no  parts  with  the  function  to  receive,  store,  and  finally  give  up  the  energy 
delivered  by  the  steam  at  the  beginning  of  the  stroke  as  must  be 
done  when  steam  is  used  expansively.  Consequently  in  this  form  of 
pump  the  only  method  of  using  steam  is  to  exhaust  it  from  the  high- 
pressure  cylinder  directly  into  the  low-pressure  cylinder,  and  use  it  in 
both  cylinders  for  the  full  length  of  the  stroke  and  without  the  use  of  cut- 


FIG.  183. — DIRECT-ACTING  DUPLEX  PISTON-PUMP. 

ofifs.  To  overcome  this  disadvantage  and  to  attain  the  economy  possible 
with  greater  rates  of  expansion,  and  still  obtain  the  compactness  of  this 
type  of  pumping-machinery,  various  types  of  compensators  have  been 
introduced.  The  Worthington  device  (Fig.  184)  is  perhaps  the  best- 
known  type.  In  this  machine  the  energy  of  the  steam  at  the  beginning 
of  the  stroke  not  only  overcomes  the  resistance  of  the  water  pumped, 
but  also  forces  the  hydraulic  pistons  at  the  front  end  of  the  pump  against 
a  fixed  pressure  stored  in  an  accumulator.  When  the  center  of  the  stroke 
is  reached  this  stored  energy  is  gradually  returned  to  the  pump  after  the 
steam  is  cut  off  and  when  it  is  expanding  in  the  cylinder.  A  decided 


D  ISP  LA  CEMEN  T-f  UMPS. 


65S 


656 


PUMPING-MA  CHINER  Y. 


FIG.  185. — HEISLER  PUMP  WITH  COMPENSATOR. 


DISPLA  CEMENT-P  UMPS. 


657 


658 


PUMPING-MA  CHINER  Y. 


FIG.  187.— ALLIS  VERTICAL  TRIPLE-EXPANSION  PUMPING-ENGINE. 


D  ISP  LA  CEMENT-PUMPS. 


659 


increase  in  the  economy  of  operation  of  this  type  of  pumps  results. 
Another  type  of  compensator  of  considerable  promise  is  the  Heisler 
Compensator  (Fig.  185).  In  this  form  of  compensator  the  cylinder  of 
one  side  at  full  steam-pressure  transmits  a  portion  of  its  force  to  aid 
the  other  side,  which  is  working  expansively. 

The  greatest  economy  in  steam-pumping  machinery  has  been 
developed  by  what  is  known  as  the  crank  and  fly-wheel  types  of  steam- 
pumps.  Fig.  1 86  illustrates  the  Gaskill  horizontal  type  of  crank  and 
fly-wheel  pumps,  and 'Fig.  187  illustrates  the  Allis  vertical  crank  and 
fly-wheel  type  now  manufactured  by  most  of  the  leading  pump-makers 
of  the  United  States. 

Hydraulic  pumps  are  pumps  arranged  very  much  after  the  style  of 
direct-acting  high-pressure  steam-pumps,  but  in  which  water  under 
pressure  is  used  in  the  power-cylinder.  They  are  not  in  common  use, 
but  are  occasionally  applicable.  The  exhaust  from  the  power  end  is 
often  wasted  into  the  discharge-pipe  from  the  pump  end. 

676.  Rotary  Pumps. — In  the  rotary  type  of  displacement- pumps  two 
revolving  pistons  rotate  in  a  pump-case,  which  they  accurately  and 


FlG.   188. — CONNERSVILLE  ROTARY  PUMPS  WITH  TURBINE. 

completely  fill  (Fig.  181  (<?));  the  rotation  of  these  pistons  alternately 
inspires  and  discharges  the  water  to  be  raised.  These  pumps  act  without 
the  use  of  suction-  or  discharge-valves.  A  plant  consisting  of  two  such 
pumps  operated  by  a  turbine  water-wheel,  as  installed  at  Connersville, 
Indiana,  for  city  water-works  purposes,  is  illustrated  in  Fig.  188. 


66O  P  UMPING-MA  CHINER  Y. 

t 

677.  Air  and  Steam  Displacement-pumps. — Other  forms  of  displace- 
ment-pumps are  those  which  use  air  or  steam  as  the  displacing  agency. 
A  common  type  of  air  displacement-pump  is  the  Merrill  Pump,  which 
consists  of  two  cylinders,   set  below  the  water-surface;    the  water  is 
admitted  to  each  cylinder  alternately  by  gravity  and  is  forced  from  the 
cylinder  by  the  direct  pressure  of  compressed  air,  which  is  then  ex- 
hausted into  the  atmosphere.      In  the  Harris  displacement-pump  (Fig. 
182  (c)  )  the  air  used  to  displace  the  water  is  returned  directly  to  the  inlet 
of  the  compressor,  and  is  forced  by  the  compressor  into  the  second 
chamber,  thus  utilizing  the  work  already  done  and  effecting  a  consider- 
able economy  in  the  use  of  air.    The  steam  vacuum-pump  (Fig.  1 82  (e)  ) 
operates  on  somewhat  similar  lines ;  but  in  this  case  the  condensing  of 
the  steam  is  an  important  factor.      Steam  is  admitted  to  a  chamber  and 
condensed  therein  by  a  spray  of  water,  thus  creating  a  vacuum  which 
inspires  the  water;  the  steam  is  again  applied  at  full  boiler-pressure 
and  the  water  forced  by  the  incoming  steam  through  a  discharge-valve 
and  pipe,  after  which  the  steam  is  again  condensed  and  the  operation 
repeated.      Such  pumps  commonly  consist  of  two  chambers,  so  that  a 
comparatively  continuous  discharge  of  water  results. 

678.  Continuous-flow   Pumps. — An   additional   variety  of  displace- 
ment-pumps, which  differ  from  those  described,  are  the  continuous-flow 
pumps.      The    most    common    type    of  these    pumps  is   the   ordinary 
chain-pump,  where  enlarged  piston-links  on  the  chain  partially  or  com- 
pletely fill  a  pipe  or  passage  through  which  they  pass  in  one  direction. 
As   the  chain   passes  below  the  water   and  into  the   pipe,  the  spaces 
between  the  piston-links  are  filled  successively  and  the  water  discharged 
at  the  outlet  as  the  pistons  pass  it.     The  screw-pump  also  has  a  similar 
action,    the    displacement  being   produced  by  the  screw-blade.      The 
"UM  type   of  pump  (Fig.   181    (d))   is   a  less-known  variety  of  the 
same  class.      A  third  type  of  continuous-flow   pump    is    the   Johnson 
Deep-well  Pump.    In  this  pump,  by  the  use  of  a  Whitworth  quick-return 
motion,  the  double  pistons  make  a  quick  down-stroke,  during  which 
time  they  are  free  from  load,  and  a  slow  up-stroke  under  load.      One 
piston  of  this  pump  is  always  on  the  up-stroke. 

(2)  Impeller -pumps. 

679.  Action  of  Impeller-pumps. — The  second  great  class  of  pumps 
is  that  of  the   Impeller-pumps,  in  which  a  volume  of  water  is  moved 
by   the    continuous    application   of  power    through   some    mechanical 
agency  or  medium.      These  pumps  consist  of  the  centrifugal  pumps 
and    the  various   jet-pumps.      In    the   displacement-pump,   previously 


IMPELLER-P  UMPS. 


66 1 


described,  the  motive  energy  is  delivered  to  the  water  by  a  direct 
pressure  which  displaces  the  water  and  which  must  be  equal  in  amount 
to  the  head  against  which  the  water  is  pumped  and  to  various  fric- 
tion losses  in  the  pumping-machinery  and  discharge-pipes.  In  the 
class  of  Impeller-pumps  the  energy  is  applied  to  the  water  by  means 
of  pressure  due  to  the  velocity  of  either  a  mechanical  agency,  as  in  the 
centrifugal  pumps,  or  of  a  fluid  agency,  as  in  the  jet-pumps. 

680.  Centrifugal   Pumps. — For    falling  bodies   we    have  the  well- 

v* 
known  formula  h  —  — ;  that  is  to  say,  the  velocity  v  is  generated  by 

a  fall  from  the  height  h ;  consequently  when  we  reverse  the  action  and 
generate  pressure  by  the  application  of  velocity  we  should,  theoreti- 
cally, have  the  same  condition,  and  a  velocity  v  =  \/2gh  should  be 
capable  of  generating  a  head  h.  In  the  centrifugal  type  of  pump  (Fig. 
181  (/")  )  the  velocity  of  the  periphery  of  the  impeller  must  ordinarily 
exceed  the  velocity  given  by  the  above  formula.  A  pump  which  acts 
strictly  as  a  centrifugal  pump  must,  however,  have  straight  radial 
vanes  or  impellers.  As  soon  as  the  vanes  are  curved,  as  is  done  in 
practically  all  centrifugal  pumps  now  made  (Fig.  189),  an  additional 


FIG.  189. — SECTION  OF  ROCKFORD  CENTRIFUGAL  PUMP. 

force  results,  and  the  pump  ceases  to  depend  solely  on  centrifugal 
force.  The  greater  the  curve  of  the  vanes  the  more  important  becomes 
the  action  of  the  new  force,  which  is  the  resultant  of  the  pressure 
exerted  by  the  inclined  surface  of  the  vane,  and  which  acts  more  with  a 
displacement  than  a  centrifugal  effect,  as  in  the  case  of  the  screw-pump. 


66  2  p  UMPING-MA  CHINER  Y. 

Centrifugal  pumps  may  be  classed  in  various  ways  according  to 
their  design  and  arrangement,  as  shown  in  the  table  of  classification. 
Their  selection  depends  on  the  various  uses  to  which  they  are  to  be 
put,  the  method  selected  for  the  application  of  power,  and  various 
other  factors  incidental  to  the  installation. 

Fig.  189  illustrates  a  vertical  side-suction  centrifugal  pump  with 
impeller  of  the  inclosed  type,  as  used  in  the  Rockford,  Illinois,  deep- 
well  pumping-plant  (see  Fig.  62,  page  316). 

681.  Jet-pumps.  —  Jet-pumps  (Fig.  182  (a))  are  arranged  to  utilize  the 
velocity  energy  of  water-,  steam-,  or  air-jets.  In  all  of  this  class  of 
pumps  a  moving  jet  of  the  liquid  used  is  delivered  through  a  restricted 
throat,  drawing  with  it  the  water  to  be  raised,  to  which  the  velocity 
energy  is  delivered.  Water,  steam,  and  air  have  each  particular 
attributes  of  their  own  in  their  application  to  this  class  of  pumps.  The 
air  especially  has  an  additional  effect  not  due  to  the  velocity,  in  that  it 
reduces  the  specific  gravity  of  the  rising  column  of  water,  and  may, 
under  proper  conditions,  cause  an  overflow  in  the  column  so  lightened 
(Fig.  1  82  (</)). 

This  class  of  air-pumps,  called  "  air-lift  "  pumps,  has  recently  been 
quite  widely  applied  to  raising  large  quantities  of  water  from  bore-holes. 
These  pumps  are  not  highly  efficient,  but  are  capable  of  raising  a  larger 
amount  of  water  from  a  small  hole  than  any  other  method.  For 
reasonable  efficiency  the  submergency  of  the  discharge-pipe  should  be 
at  least  60  per  cent  of  its  total  height,  or  one  and  one-half  times  the 
height  to  which  the  water  is  raised  above  the  surface. 

The  formula  commonly  used  for  determining  the  relation  of  the 
various  factors  in  an  air-lift  problem  is 


in  which  q  =  gallons  of  water  per  minute  ; 

A  =  cubic  feet  of  free  air  per  minute  ; 

h  =  height  of  lift  in  feet  from  water-surface  to  point  of  dis- 
charge. 

(3)  Impulse-  pumps. 

682.  The  third  class  of  pumps  comprises  those  of  the  impulse  type, 
which  raise  water  by  the  periodical  application  of  force  suddenly  applied 
and  suddenly  discontinued.  The  hydraulic  ram  is  the  principal  repre- 
sentative of  this  class  (Fig.  182  (£)).  In  this  pump  the  pulse-valve  or 


PUMP   DETAILS.  663 

waste -valve  is  opened  automatically  either  by  gravity  or  some  other 
agency  (such  as  a  spring,  as  in  the  figure)  properly  applied.  The  water 
in  the  drive-pipe  wastes  through  this  valve,  acquiring  a  velocity  which 
in  turn  generates  sufficient  friction  to  suddenly  close  the  valve,  thus 
causing  an  impact  or  impulse  which,  when  properly  applied,  opens  the 
check-valve  and  delivers  a  certain  proportion  of  water  into  the  air- 
chamber  and  delivery-pipe.  As  the  impulse  dies  away  the  waste  valve 
again  opens  and  the  cycle  is  repeated. 

(4)  Bucket-pumps. 

683.  The  fourth  class  of  pumps  is  composed  of  the  bucket-pumps, 
which   include   all  those  in  which  definite  receptacles  are  alternately 
filled,  raised,  and  emptied.      These  pumps  are  often  of  the  form  of  the 
continuous-conveyor  type,  in  which  a  series  of  buckets  attached  to  a 
belt  and  chain  are  dipped  in  the  water,  filled,  elevated,  and  emptied. 

PUMP   DETAILS. 

684.  General  Rules. — The  class  of  any  pump  must  modify  largely 
the  details  used  in  its  construction.      A  few  general  rules  will  apply, 
however,  in  all  cases. 

All  pumps  should  be  so  designed  and  connected  as  to  admit  the 
free  and  unrestricted  flow  of  water.  They  should  be  free  from  all  air- 
traps,  and  when  changes  in  the  direction  of  flow  are  necessary,  large 
easy  bends  should  be  used. 

685.  Valves. — Almost  all  displacement-pumps  require  the  use  of 
admission-  and  discharge-valves.      These  valves  are  a  serious  source  of 
loss  of  efficiency  in  this  class  of  machinery.      Frequently  as  high  as  12 
to  1 5  feet  of  head  is  lost  in  the  valve-  and  water-passages  even  of  high- 
grade  pumping-engines. 

The  primary  requisites  of  pump- valves  are  as  follows : 

They  should  close  tightly,  to  avoid  loss  from  leakage. 

They  should  close  promptly,  to  avoid  loss  from  slip. 

They  should  have  small  lift,  to  permit  of  prompt  closing. 

They  should  have  large  waterways. 

They  should  open  easily  and  without  large  extra  pressure. 

They  should  present  small  resistance  to  flow,  in  order  to  reduce 
the  friction  losses  to  a  minimum. 

They  should  be  simple,  readily  accessible,  and  readily  removable 
to  facilitate  repairs. 

The  type  of  valve  most  widely  used  is  shown  in  Fig.  190(0).    These 


664 


P  UMP ING-MA  CHINE R  Y. 


(a)  Ordinary  Valve.  (£)  Method  of  Grouping  Valves. 


(c)  Troy  Valve. 


(<t)  Battle  Creek  Valve. 


(/)Riedler  Valve. 


Ball  Valve.  (h)  Cone  Valve. 

FIG.  190. — TYPES  OF  PUMP- VALVES. 


PUMP   DETAILS.  66$ 

valves  are  ordinarily  from   3^  to  4^  inches  in  diameter.      The  valve- 
seat,  stem,  cover-plate,  and  spring  should  be  of  bronze. 

True  cylindrical  springs  are  preferable  to  conical  springs.  The 
disks  should  be  of  medium  hard  India  rubber,  vulcanized  sufficiently 
to  give  it  firmness.  For  hot-water  pumps  this  disk  should  be  of  hard 
rubber.  The  lift  of  the  valve  is  limited  by  the  stem-head,  and  the  stem 
prevents  its  drifting  sidewise.  A  sufficient  number  of  these  valves  are 
grouped  in  the  valve-chamber  to  give  the  desired  waterway.  In  poor 
pumps  this  is  commonly  not  over  25  per  cent  of  the  plunger  area; 
while  high-grade  pumps  will  have  a  free  waterway  of  from  50  to  100  per 
cent  of  the  plunger  area,  according  to  the  speed  of  operation  and 
number  of  reversals  of  the  plunger. 

Fig.  190  (^)  shows  the  arrangement  of  these  valves  as  commonly 
used  in  large  pumping-engines.  Several  of  these  groups  may  be  used 
in  a  single  valve-chamber. 

Fig.  190  (c)  shows  the  Troy  valve  used  in  the  Gaskill  pumping- 
engine.  It  is  a  small  valve  having  a  diameter  of  about  ij  inches. 
No  spring  is  used  with  this  valve. 

Fig.  190  (X)  shows  a  metal  valve  used  in  the  Battle  Creek  pumps. 
In  this  valve  the  lift  is  limited  by  the  walls  of  the  valve-chamber. 
The  curved  center  guides  the  liquid  through  the  opening  with  minimum 
friction  and  small  eddy  losses,  as  the  liquid  leaves  the  curve  on  a  tan- 
gent when  the  valve  is  fully  open. 

Fig.  190  (e)  shows  the  form  of  valves  used  in  the  Walker  pump. 
The  valve  disk  or  cover  is  of  rubber  of  a  rectangular  shape  thickened 
at  the  sides,  the  center  forming  a  hinge  and  the  sides  forming  the 
valve-covers.  The  upper  portion  of  the  figure  shows  the  arrangement 
of  the  suction-valves ;  the  lower  portion  shows  the  discharge-valves. 

Fig.  190  (_/")  shows  the  Riedler  valve.  Only  one  valve  of  this  type 
is  used  on  each  inlet  or  outlet  of  the  Riedler  pumps.  This  valve  is 
mechanically  closed  just  as  the  direction  of  motion  of  the  pump-piston 
is  reversed.  By  the  use  of  this  valve,  large  waterway  is  provided,  and 
by  its  mechanical  closing,  slip  and  pound  is  prevented  when  the  pump 
reverses. 

Fig.  190  (g)  shows  a  ball  valve  which  is  commonly  used  in  deep- 
well  pump-cylinders.  The  valve  is  usually  a  bronze  sphere  and  seats 
in  a  bronze  ring  simply  by  its  own  weight.  Its  lift  is  limited  as  shown 
in  the  cut.  Groups  of  such  valves  are  sometimes  arranged  in  valve- 
chambers  for  reciprocating-pumps. 

Fig.  190  (Ji)  shows  the  Downie  cone  valve,  which  is  also  used  for 
deep-well  cylinders.  This  valve  consists  of  two  cones,  the  outside  one 


666  P  UMPING-MA  CHINER  Y. 

being  movable.  When  this  outside  cone  is  seated  the  valve  is  closed, 
the  solid  metal  of  each  cone  closing  the  apertures  in  the  other.  When 
the  valve  is  raised  the  apertures  in  the  cones  are  opposite  and  the 
water  passes  readily  through  the  openings. 

Rotary  and  centrifugal  pumps  can  be  operated  without  valves  of 
any  description,  but  it  is  desirable  with  these  pumps,  as  with  all 
others  which  are  used  for  water-works  purposes,  to  use  a  check-valve 
on  the  discharge,  so  that  in  case  any  accident  should  happen  to  the 
machinery,  the  reservoir,  stand-pipe,  or  other  device  for  storing  water 
will  not  be  emptied  through  the  broken  pump  into  the  pumping-station. 
In  the  case  of  rotary  and  centrifugal  pumps  the  check-valve  is  particu- 
larly necessary,  as  when  the  power  ceases  to  be  applied  the  pump  will 
discharge  the  stored  water  back  through  the  pump  and  suction-pipe 
into  the  source  of  supply. 

686.  Air  and  Vacuum  Chambers. — All  displacement-pumps  except 
the    continuous-flow  variety,   and  even  those  unless  the  continuity  of 
flow  is  perfect,  should  be  provided  with  vacuum-  and  air-chambers  on 
the  inlet-  and  discharge-pipes  in  order  to  take  up  the  irregularities  of 
flow  due  to  intermittent  or  irregular  action  and  prevent  injurious  and 
sometimes  destructive  shocks. 

The  size  of  air-chamber  depends  on  the  condition  of  working. 
Since  the  function  of  the  air-chamber  is  to  eliminate  irregularities,  the 
greater  the  irregularities  the  larger  the  chamber  should  be.  Hence, 
with  a  high-speed  pump  or  a  pump  forcing  water  through  great  length 
of  pipe  or  against  a  high  head,  the  air-chamber  should  be  enlarged  over 
what  would  be  needed  with  slow-running  pumps  and  low  lifts. 

Triplex  pumps  under  low  lifts  may  be  provided  with  air-chambers 
of  a  capacity  equal  to  a  single  displacement  of  the  piston,  while  for 
single-cylinder,  double-acting  pumps  the  air-chamber  should  be  from 
six  to  eight  times  this  size.  Means  for  supplying  air-chambers  with  air 
should  also  be  provided.  In  suction-pumps  this  can  be  readily  accom- 
plished by  connecting  a  small  check-valve  with  a  pump-chamber  so 
that  when  the  pump  inspires  it  will  draw  in  a  small  amount  of  air  with 
the  water.  A  globe  valve  outside  of  the  check-valve  will  control  the 
operation  of  the  air-inlet  as  may  be  desired. 

It  is  desirable  to  provide  air-chambers  with  a  gauge-glass,  so  that 
the  amount  of  air  in  the  chamber  will  be  known  (Fig.  179). 

687.  Inlet-  or  Suction-pipes. — Pumping-machinery  may  receive  the 
water  to  be  pumped  in  two  ways. 

First,  the  water  may  flow  to  the  machine  by  gravity,  the  machine 


PUMP   DETAILS.  66? 

being  below  the  water  a  depth  at  least  equal  to  the  sum  of  the  velocity 
and  friction  heads. 

Second,  the  water  may  be  raised  through  a  pipe  into  the  machine 
by  atmospheric  pressure  or  suction. 

Suction  consists  in  creating  a  more  or  less  perfect  vacuum  in  the 
suction-chambers  and  suction-pipe  and  rilling  the  same  with  water  by 
atmospheric  pressure.  Before  a  suction-pump  will  work  properly  it 
must  be  able  to  create  such  a  vacuum  or  to  ' '  prime  ' '  itself.  The 
priming  of  a  pump  in  which  there  is  no  water  requires  either  the  filling 
of  the  pump  with  water  from  some  other  source  and  the  consequent 
expulsion  of  the  air,  or  that  the  empty  pump  shall  act  as  an  air- 
pump  and  thus  remove  the  air.  A  centrifugal  pump  cannot  act  as  an 
air-pump.  It  must  therefore  be  below  the  water  to  prime  itself.  In 
order  to  prime  a  pump  which  cannot  act  as  an  air-pump  it  must  be  pro- 
vided with  a  foot-valve  which  will  prevent  the  loss  of  water  from  some 
higher  source,  or  a  priming-pump  (i.e.,  a  small  air-pump)  must  be 
attached  to  it. 

Reciprocating-pumps  can  be  primed  by  the  piston  action  much 
more  readily  than  rotary  pumps,  but,  especially  on  high  lifts,  should 
be  provided  with  priming-pipes. 

For  perfect  suction  and  satisfactory  operation  care  must  be  taken 
to  secure  the  following  conditions : 

1.  The  openings  between  the  moving  and  fixed  parts  of  the  pump 
must  be  as  small  as  possible,  that  is,  the  pump  must  be  well  packed 
between  the  fixed  and  moving  parts. 

2.  The  suction-chambers  and  pipes  must  be  air-tight. 

3.  All  air-traps  must  be  avoided  in  all  suction  members. 

4.  All  unnecessary  bends  must  be  avoided,  and  the  suction-pipe 
should  be  made  as  short  and  direct  as  possible.      The  pump  should  be 
placed  as  near  the  water  as  possible,  and  the  suction-pipe  should  be  of 
proper  size.      The  possibility  of  suction  is  limited  (see  Table  No.  37, 
page  224). 

The  amount  of  available  suction-head  must  never  be  less  than  the 
sum  of  the  following  heads  commonly  lost  in  suction-pipes  and  the 
suction-passages  of  pumps : 

1.  Influx  loss  at  end  of  suction-pipe  (see  eq.  (36),  page  248). 

2.  Velocity  loss  in  suction-pipe  (see  Art.  657). 

3.  Friction  loss  in  suction-pipe  (see  Fig.  34,  page  243). 

4.  Friction  loss  in  suction-valve  and  water-passage  of  pump  (see 
Art.  685). 


668  P  UMP  ING-MA  CHINER  Y. 

5.  Acceleration  head,  or  the  pressure  necessary  to  accelerate  the 
water  where  the  flow  is  not  uniform. 

6.  Vapor  tension  of  water  (see  Table  No.  38,  page  225). 

If  the  sum  of  these  losses  together  with  the  head  against  which  the 
water  is  to  be  raised  by  suction  is  greater  than  the  available  atmos- 
pheric pressure,  the  pump  will  not  work  to  its  proper  capacity  and  may 
not  raise  the  water  at  all. 

688.  Location  of  Pumping-machinery  with  Respect  to  the  Level  of  the 
Water  Drawn  from. — The  conditions  under  which  the  water-supply 
must  be  obtained  will  to  a  large  extent  control  the  type  of  machinery 
which  must  be  used.  As  before  noted,  it  is  always  desirable  to  place 
the  water  end  of  the  machinery  as  near  the  water  as  possible,  while  the 
power  end  must  usually  be  placed  above  high  water,  or,  if  placed 
below  the  water,  it  must  usually  be  arranged  in  a  water-tight  shaft  or 
compartment.  The  ordinary  horizontal  type  of  reciprocating  pump- 
ing-machinery  should  seldom  be  placed  more  than  18  feet  above  the 
lowest  water  it  will  be  called  upon  to  handle.  A  suction  lift  of  24 
to  26  feet  is,  however,  sometimes  possible.  Where  the  distance 
from  pump  to  water-surface  is  greater  than  the  maximum,  and 
especially  where  large  volumes  of  water  are  to  be  handled,  such  lifts 
become  hazardous  or  impossible  and  other  types  of  pumping-machinery 
must  be  used  or  other  methods  of  locating  the  machinery  employed. 

The  most  obvious  method  of  reaching  water  when  it  is  below  suction 
distance  is  to  sink  the  pump  to  such  a  depth  below  the  surface  as  to 
bring  it  within  easy  suction  distance  of  the  water.  When  the  distance 
is  not  too  great  and  where  conditions  are  favorable,  this  can  readily  be 
done,  and  this  method  has  frequently  been  employed. 

The  water  ends  of  pumps  demand  but  comparatively  little  attention. 
The  flow  of  water  lubricates  most  of  the  parts  to  a  considerable  extent, 
and  such  parts  as  are  not  in  this  way  sufficiently  lubricated  can  be 
easily  cared  for  by  attention  at  occasional  intervals. 

The  motor  end  of  the  pump,  however,  is  usually  much  more  com- 
plicated and  necessarily  requires  more  particular  and  constant  attention. 
When,  therefore,  the  depth  at  which  the  water  is  obtained  is  consider- 
able, it  is  often  desirable  to  rearrange  the  design  of  the  pumping- 
machinery,  placing  the  water  end  within  easy  suction  reach  of  the 
supply,  and  the  motor  end  within  ready  access  from  the  surface  and 
near  the  boilers  or  other  source  of  power.  This  has  given  rise  to 
various  types  of  vertical  machinery  which  fulfill  these  conditions  with 
more  or  less  success. 

The  cost  involved  in  the  construction  of  large  shafts,  especially  in 


PUMP   DETAILS. 

unfavorable  locations,  may  make  it  desirable  to  economize  in  shaft 
room.  Special  types  of  pumps  have  been  designed  to  suit  these 
requirements,  and  the  same  result  may  be  obtained  under  favorable 
conditions  by  the  enlargement  of  the  base  of  the  shaft  and  the  use  of 
ordinary  types  of  horizontal  pumps  located  near  the  shaft  base  where 
such  arrangement  is  permissible.  The  arrangement  of  the  machinery 
with  this  end  in  view  is  shown  in  the  plant  installed  at  Rockford, 
Illinois  (page  318).  The  water  end  of  this  pumping-plant  consists  of 
high-grade  centrifugal  pumps,  while  vertical  compound  condensing 
engines  furnish  the  motive  power,  and  rope  transmission  is  the  means 
of  connecting  pumps  and  engines.  The  above  arrangement  assumes 
the  ability  to  concentrate  the  water  at  one  central  shaft  in  which  the 
machinery  is  located.  This  may  be  done  in  general  in  the  following 
ways: 

1 .  By  the  construction  of  a  large  open  well  in  an  open  or  coarse 
water-bearing  stratum.      Such  plants  have  been  satisfactorily  adopted 
for  small  and  medium  quantities  of  water. 

2.  The  various  wells  may  be  connected  by  pipes  laid  as  deeply  as 
possible  in  trenches  open  from  the  surface. 

3.  The  various  wells  may  be  connected  by  tunnels  into  which  the 
water  may  empty  direct,  or  the  wells  may  be  connected  by  pipes  laid 
in  the  tunnels  and  connected  to  the  suction  side  of  the  pumps. 

Where  shaft  and  tunnel  work  is  expensive  it  will  sometimes  become 
desirable  to  install  small  isolated  plants  on  each  well,  which  may  be 
operated  singly  or  together  as  the  water  required  demands.  For  this 
use  one  or  more  small  shafts  may  be  built  and  connected  directly  with 
the  water-bearing  stratum,  or  one  or  more  bore-hole  wells  may  be  sunk, 
and  in  such  shafts  or  wells  the  secondary  machinery  may  be  placed. 

Separate  steam-pumps  may  be  applied  to  such  wells,  but  usually 
such  pumps  are  far  from  economical.  Power  may,  however,  be  gen- 
erated in  various  ways  from  a  central  and  more  economical  generator 
and  transmitted  to  the  separate  wells  by  electrical  transmission,  by 
pneumatic  transmission,  or  by  hydraulic  transmission. 

At  De  Kalb,  Illinois,  where  the  water  is  raised  from  deep  wells 
from  a  depth  of  1 50  feet  below  the  surface,  electrical  transmission  is 
used,  the  water  being  raised  by  separate  pumps  and  forced  into  the 
reservoir  near  the  surface,  from  which  it  is  taken  by  the  service  pumps 
(see  Fig.  180),  and  pumped  into  the  mains  and  stand-pipe. 

At  Peoria,  Illinois,  Mr.  D.  H.  Maury,  Mem.  Am.  Soc.  C.  E.,  has 
developed  a  unique  and  efficient  method  of  hydraulic  transmission. 
The  water  which  operates  the  secondary  plants  is  taken  from  the  mains 


6/0  P  UMPING-MA  CHINER  Y. 

supplied  by  the  high-duty  pumping-engine.  The  secondary  installa- 
tions are  operated  by  impulse  water-wheels  attached  to  horizontal 
centrifugal  pumps.  The  water  used  to  operate  the  impulse-wheels 
together  with  the  water  pumped  by  the  centrifugal  pumps  is  returned 
to  the  main-supply  well. 

The  centrifugal  pump  is  widely  used  on  the  Pacific  coast  for  such 
purposes,  and  for  lifts  of  1 50  feet  or  less  can  often  be  operated  to  an 
advantage.  Its  use  throughout  the  eastern  part  of  the  United  States 
is  not  so  general;  the  plant  at  Rockford,  Illinois,  (see  Figs.  62  and 
189,)  being  perhaps  the  highest  lift  of  any  attempted  in  the  East, 
namely,  106  feet,  when  pumping  to  the  full  capacity  of  the  plant. 

DUTY   AND    EFFICIENCY    OF   PUMPING-MACHINERY. 

689.  Measures  of  Duty. — While  the  efficiency  of  pumping-machinery 
may  be  measured  by  the  units  included  in  the  tables  previously  given, 
there  is  also  another  measure  of  efficiency  which  is  largely  used  in  con- 
sidering pumping-plants  and  pumping-machinery.  This  measure  of 
efficiency  is  termed  "  duty  "  and  represents  the  ratio  of  work  done  to 
the  energy  expended  in  doing  it.  Duty  may  be  expressed  in  almost 
any  units,  but  in  pumping  it  usually  represents  the  ratio  of  foot-pounds 
of  work  done  to  a  fixed  weight  of  coal,  or  steam,  or  to  a  fixed  number 
of  heat-units  used. 

The  terms  most  generally  used  to  express  duty  of  pumping-engines 
are  foot-pounds  duty  per  100  pounds  of  coal,  per  1000  pounds  of  steam, 
or  per  1,000,000  heat-units. 

It  must  be  understood  that  the  duties  expressed  in  the  above  units 
are  not  necessarily  equivalent,  but  vary  largely  in  actual  value.  For 
example,  the  Indianapolis  Water  Company's  engine,  built  by  the  Snow 
Steam-pump  Company,  is  said  to  have  developed  a  duty  of  167.8 
million  foot-pounds  for  each  1000  pounds  of  dry  steam,  but  only  150.1 
million  foot-pounds  for  each  1,000,000  heat-units. 

Duty  based  on  coal  is  very  indefinite,  for  coal  varies  largely  in  its 
potential  energy  or  calorific  value  (see  Table  No.  85). 

When  coal  is  considered  the  plant  efficiency  must  also  be  included. 
This  may  include  boilers,  steam-pipe,  feed-pump,  heater,  etc.,  which 
have  not  necessarily  any  relation  to  the  individual  efficiency  of  the 
pump  itself.  Duty  based  on  coal  should  therefore  only  be  used  where 
the  entire  plant  is  considered  and  when  the  class  of  coal  is  also 
specified. 

Duty  based   on  steam  is  more  specific,  but  hardly  sufficiently  so. 


DUTY   OF  PUMPING-MACHINERY. 


6/1 


TABLE  NO.  91. 

DUTY,     CORRESPONDING    AMOUNT    OF    COAL    PER    H.P.    PER     HOUR,     AND     CORRESPONDING 
AMOUNT    OF    COAL    REQUIRED    TO    RAISE    I.OOO.OOO    GALLONS    IOO    FT.    HIGH. 


Duty 
in  Mil- 
lion 
Ft.-lbs. 

Iti 

<j  a 

•3* 

•oK  S' 

Is! 

eu 

|s 

Sfc 
58 

& 

445 

Duty 

in  Mil- 
lion 
Ft.-lbs. 

Pounds  of  Coal 
per  H.P.  per 
Hour. 

II 

58 

l*i 

JS'SSS 

Duty 
in  Mil- 
lion 
Ft.-lbs. 

Pounds  of  Coal 
per  H.P.  per 
Hour. 

|1 

gh 

58 

v-  M 

Nl 

3OB 

Duty 

in  Mil- 
lion 
Ft.-lbs. 

Pounds  of  Coal 
per  H.P.  per 
Hour. 

Lbs.  per  Million 
Gals.  100  Feet 
High. 

I 

198.00 

83398 

43 

4.60 

1939 

84 

2.36 

992 

125 

1.58 

667 

2 

99.00 

41699 

44 

4-50 

1895 

85 

2-33 

981 

126 

i-57 

662 

3 

66.00 

27799 

45 

4.40 

1853 

86 

2.30 

969 

127 

1.56 

656 

4 

49-50 

20849 

46 

4-30 

1813 

87 

2.28 

958 

128 

1-55 

651 

5 

39-60 

16679 

47 

4.21 

1774 

88 

2.25 

947 

129 

•53 

646 

6 

33-00 

13899 

.  48 

4-12 

1737 

89 

2.22 

937 

130 

•52 

64I 

7 

28.29 

11914 

49 

4.04 

1702 

90 

2.20 

926 

131 

.51 

636 

8 

24-75 

10424 

50 

3.96 

1668 

91 

2.18 

916 

132 

•50 

632 

9 

22.00 

9266 

5i 

3-88 

1635 

92 

2.15 

906 

133 

•49 

627 

10 

19.80 

8340 

52 

3.80 

1604 

93 

2.13 

890 

134 

.48 

622 

ii 

18.00 

7561 

53 

3-73 

1573 

94 

2.  II 

887 

135 

.47 

618 

12 

16.50 

6930 

54 

3-66 

1544 

95 

2.08 

878 

136 

.46 

613 

13 

15-23 

6413 

55 

3.60 

1516 

96 

2.06 

868 

137 

•45 

609 

14 

14.14 

5937 

56 

3-53 

1489 

97 

2.04 

859 

138 

•43 

604 

15 

13.20 

556o 

57 

3-47 

1463 

98 

2.02 

851 

139 

.42 

600 

16 

12.37 

5212 

58 

3.41 

1437 

99 

2.OO 

842 

140 

.41 

595 

17 

11.64 

4906 

59 

3.35 

1414 

IOO 

.98 

834 

141 

.40 

591 

18 

II.OO 

4633 

60 

3.30 

1389 

101 

.96 

825 

142 

•39 

587 

19 

10.42 

4384 

61 

3-24 

1367 

IO2 

•94 

8i7 

143 

.38 

583 

20 

9.90 

4170 

62 

3-19 

1345 

103 

.92 

809 

144 

•37 

579 

21 

9-43 

3971 

63 

3-14 

1323 

104 

.90 

802 

145 

•37 

575 

22 

9.00 

3791 

64 

3.09 

1303 

105 

.89 

794 

146 

•36 

57* 

23 

8.60 

3626 

65 

3-04 

1283 

1  06 

.87 

786 

147 

•35 

567 

24 

8.25 

3475 

66 

3.00 

1263 

107 

•85 

779 

148 

•34 

563 

25 

7-92 

3336 

67 

2-95 

1244 

108 

.83 

772 

149 

•33 

560 

26 

7.61 

3208 

68 

2.91 

1226 

109 

.82 

765 

150 

•32 

556 

27 

7-33 

3089 

69 

2.87 

1208 

no 

.80 

758 

151 

.31 

542 

28 

7.07 

2978 

70 

2.83 

1191 

in 

•78 

75i 

152 

•30 

539 

29 

6.83 

2876 

7i 

2-79 

1174 

112 

•77 

744 

153 

.29 

534 

30 

6.60 

2780 

72 

2-75 

1158 

H3 

•75 

738 

154 

.28 

531 

31 

6.38 

2690 

73 

2.71 

1142 

114 

•74 

731 

155 

.27 

528 

32 

6.18 

2606 

74 

2.67 

1127 

H5 

.72 

725 

156 

•27 

525 

33 

6.00 

2527 

75 

2.64 

III2 

116 

•7i 

719 

157 

.26 

522 

34 

5-82 

2433 

76 

2.60 

1097 

117 

.69 

713 

158 

•25 

5i8 

35 

5-65 

2383 

77 

2.57 

1083 

118 

.68 

707 

159 

.24 

5i6 

36 

5.50 

2316 

78 

2-54 

1069 

119 

.66 

701 

1  60 

.24 

5" 

37 

5-35 

2254 

79 

2.50 

1055 

I2O 

.65 

695 

161 

•23 

508 

38 

5.21 

2194 

80 

2.47 

1042 

121 

.64 

689 

162 

.22 

504 

39 

5-07 

2138 

81 

2.44 

1029 

122 

.62 

683 

163 

.21 

502 

40 

4-95 

2085 

82 

2.41 

IOI7 

123 

.61 

678 

164 

.21 

499 

4i 

4.83 

2034 

83 

2.38 

IOO4 

124 

.60 

672 

165 

.20 

496 

42 

4.71 

1985 

6/2  P  UMPJNG-MA  CHINER  Y. 

Both  theory  and  practice  show  that,  with  suitable  conditions,  steam  at 
150  pounds  pressure  has  a  greater  value  than  steam  at  90  pounds 
pressure.  The  entrained  water  from  the  boiler  and  the  condensation 
in  the  steam-pipe  also  modify  the  results.  When  duty  is  based  on  the 
weight  of  steam  used,  the  terms  dry  steam  and  a  specified  pressure 
should  also  be  included. 

In  Table  No.  91  the  relation  of  duty  to  coal-consumption  and 
steam-consumption  per  horse-power  per  hour  is  shown. 

A  table  of  the  relations  of  duty  to  steam-consumption-  per  horse- 
power per  hour,  and  of  steam  required  to  raise  1,000,000  gallons  100 
feet  high,  may  be  obtained  by  multiplying  the  figures  for  coal  in  the 
respective  columns  by  10.  A  similar  table  for  heat  may  be  obtained  by 
multiplying  by  10,000.  The  corresponding  duty  values  in  such  tables 
are  not,  however,  necessarily  equivalent. 

The  duty  of  any  pumping-engine  or  pumping-plant  may  be  calcu- 
lated from  the  formula: 

weight  of  water  pumped  X  head  X  duty  unit 
amount  of  energy  used 

The  "duty  unit"  is  100  for  coal,  1000  for  steam,  and  1,000,000 
for  heat-units.  The  * '  amount  of  energy  used  ' '  is  the  total  weight  of 
coal  or  steam,  or  the  number  of  heat-units  used. 

It  may  be  noted  from  Table  No.  82  that  with  perfect  efficiency  the 
following  duties  should  be  developed: 

Foot-pounds. 

100  pounds  average  anthracite  coal 1,140,548,000 

100  pounds  average  bituminous  coal 991, 172,000 

1000  pounds  steam  (approximate) 778,000,000 

1,000,000  pounds  British  thermal  units 778,000,000 

From  the  above  it  will  be  noted  that  100  pounds  of  average  coal  has 
a  greater  theoretical  value  than  1000  pounds  of  steam.  Under  good 
average  conditions,  however,  not  more  than  10,000  British  thermal 
units  per  pound  of  coal  can  be  transformed  into  the  actual  potential 
energy  of  steam,  and  in  ordinary  practice  the  amount  transformed  is 
usually  much  less. 

The  above  theoretical  equivalents  should  be  compared  with  the 
results  usually  obtained  in  practice  as  shown  in  Table  No.  92. 

690.  Ordinary  Duty  and  Efficiency  of  Pumping-machinery. — Table 
No.  92  shows,  first,  the  ordinary  duty  and  efficiency  of  steam  pump- 
ing-machinery ;  second,  the  duty  and  efficiency  of  pumping-plants 


DUTY  OF  PUMPING-MACHINERY. 


673 


TABLE    NO.    92. 

DUTY    OF    PUMPING-PLANTS. 


Class. 

Duty  per  IOOD 
Pounds  Steam. 

Pounds  Steam 
per  A.H.P. 
per  Hour. 

Theoretical 
Efficiency. 
Per  cent. 

j 

i 
1 

1 

IV  \ 

y 

\ 
\ 

Max.  160 
Min.    loo 
Max.  100 
Min.      75 
Max.     40 
Min.      20 
Max.     20 
Min.      10 
Max.      6 
Min.       2 
Max.      8 
Min.       2 
Max.      4 
Min.        i 

'th  Direct-con 
75  per  cent. 

Max.    47 
Min.     37 
Max.    58 
Min.     47 
Max.     75 
Min.     67 
Max.     75 
Min.      58 
Max.    92 
Min.     75 
Max.  114 
Min.     99 

rarious    Types 
25  per  cent. 

Max.     31 
Min.     25 
Max.  22.5 
Min.      18 
Max.     14 
Min.      12 
Max.     12 
Min.       8 
Max.     10 
Min.       6 

12.3 

19.8 
19.8 
26.4 

49-5 
99.0 
99.0 
198.0 
330.0 
990.0 

247-5 
990.0 
495-0 
1980.0 

nected  Engin 

42.0 

53-5 
34-0 
42.0 
26.4 

29-5 
26.4 
34-o 
21.5 
26.4 
17.4 
20.  o 

of  Air-corn^. 

63.8 
79.0 

88.0 

IIO.O 

141.0 
165.0 
165.0 
247.0 
198.0 
330.0 

20.6 
12-9 
12.9 
9.8 

5-2 

2.6 
2.6 

i-3 
•77 
.26 
1.04 
.26 
•52 
•13 

e. 

6.1 

4.8 

7-5 
6.1 
9.8 
8.6 
9.8 
7-5 

10.2 
9.8 
14.7 
12-7 

ressors. 

4.0 
3-2 
2.9 

2-3 
1.8 
i-5 
i«5 
1.03 
1.29 
•77 

Large  well-designed  steam-pumps  

Ordinary  well-designed  steam-pumps  

Average  Duty  of  Power-pumps 
Pump  Efficient 

Simple  high-speed  engine,  non-condensing. 

Simple  Corliss  condensing   

Compound  high-speed  condensing  

Average  Duty  of  Air-lift  Pump   with  V 
Pitmp  Efficiency 

Compound  Corliss  condensing     ...           .  .  • 

Simple  Corliss  condensing  

\ 
\ 

Well-designed  high-pressure  compressor  .  . 

composed  of  power-pumps  of  75  per  cent  efficiency  direct-connected  to 
various  types  of  steam-engines,  with  steam-consumption  as  given  in 
Table  No.  89;  and  third,  the  duty  and  efficiency  of  pumping-plants 
composed  of  various  types  of  air-compressors  and  the  air-lift  pump  of 
25  per  cent  efficiency. 


6/4  P  UMPING-MA  CHINER  Y. 

These  results  may  be  considered  as  fair  average  results  of  well- 
designed  plants.  Results  much  higher  may  be  obtained  under  ideal 
conditions,  and  much  poorer  results  are  only  too  common  in  actual 
practice. 

The  efficiency  of  various  power-pumps,  and  of  some  other  pumps 
before  mentioned,  is  about  as  follows: . 

ORDINARY    EFFICIENCY    OF    PUMPS. 

Minimum.       Maximum. 

Reciprocating-pumps 60  85 

Centrifugal  pumps 50  80 

Rotary  pumps 50  80 

Displacement  air-pump  exhausting  into  at- 


,  r  20  23 

mosphere } 

Harris  displacement  air-pump 60  70 

Air-lift  pump 15  40 

With  other  values  from  between  the  limits  named  above  substituted 
in  Table  No.  92  there  will,  of  course,  be  corresponding  changes  in  the 
ultimate  duty  and  efficiency  of  the  respective  plants. 

691.  Methods  of  Analyzing  Losses  of  Energy. — From  statements 
already  made  it  will  be  seen  that  a  great  variation  in  duty  and  in 
efficiency  exists  between  the  various  types  of  pumping-plants,  and 
consequently  in  the  cost  of  their  operation.  Careful  analysis  of  various 
combinations  which  can  be  utilized  for  any  place  should  be  made  in 
order  to  obtain  a  basis  for  intelligent  comparison.  This  analysis  can 
be  made  either  analytically  or  graphically,  but  the  graphical  methods 
possess  the  advantage  of  showing  at  once  to  the  eye  the  points  at  which 
all  losses  occur,  and  where  attempts  to  economy  can  best  be  made. 

A  graphical  analysis  of  the  power  losses  in  the  centrifugal  pump- 
ing-plant  at  Rockford,  111.,  is  illustrated  in  Fig.  191.  The  diagram 
to  the  left  illustrates  the  losses  from  the  fuel  used  to  the  indicated 
horse-power  developed  in  the  engine. 

The  line  in  this  diagram  numbered  I  represents,  by  its  length,  the 
total  energy  of  the  fuel  used.  It  is  subdivided  into  one  hundred  parts. 
Diagonal  lines  drawn  from  any  point  on  this  line  to  the  focal  point  at 
the  right  will  subdivide  every  vertical  line  in  the  diagram  proportional 
to  the  percentage  line  of  the  total  energy  of  the  fuel. 

It  is  found  that,  on  account  of  natural  limitations,  not  more  than  83 
per  cent  of  the  actual  fuel-value  is  theoretically  available  in  the  furnace. 
The  length  of  the  line  No.  2  therefore  represents  the  proportion  of  the 


METHODS   OF  ANALYZING   LOSSES  OF  ENERGY. 


675 


total  energy  of  the  fuel  which  theoretically  should  be  utilized  by  the 
boiler. 

In  the  plant  in    question  only  about  75    per  cent  of  the  energy 


\ r  i \ 


theoretically  available  is  utilized,  hence  the  energy  utilized  in  the 
boiler  is  represented  by  line  No.  3,  which  is  75  per  cent  of  the  line 
No.  2,  or  about  62  J  per  cent  of  the  total  energy  of  the  fuel  burned. 


P  UMPING-MA  CHINER  Y. 

The  loss  in  the  steam-pipe  is  assumed  at  5  per  cent  of  the  boiler 
energy,  hence  there  is  delivered  to  the  engine  about  59  per  cent  of 
the  total  energy  of  the  fuel.  Of  the  total  energy  delivered  to  the 
engine  as  steam  only  about  25  per  cent  is  theoretically  available  in  the 
engine.  This  proportion  is  represented  by  line  No.  5  of  the  diagram. 
In  the  plant  in  question,  the  amount  actually  utilized  in  the  indicated 
horse-power  of  the  engine  is  about  8  J  per  cent  of  the  energy  delivered 
to  it.  This  amount  is  represented  by  line  No.  6  of  the  diagram. 
From  this  diagram  it  is  also  seen  that  the  amount  of  energy  utilized  in 
the  indicated  horse-power  of  the  engine  is  about  34  per  cent  of  the 
energy  theoretically  available  in  the  engine  and  about  5  per  cent  of  the 
total  energy  of  the  fuel  consumed. 

The  percentage  line  in  the  right-hand  diagram  is  an  enlargement 
of  the  line  representing  the  energy  utilized  in  the  indicated  horse-power 
of  the  engines  as  shown  by  line  No.  6  of  the  left-hand  diagram.  From 
this  diagram  it  will  be  noted  that  there  is  a  loss  of  about  10  per  cent 
in  engine  friction,  that  is,  the  actual  horse-power  delivered  by  the 
engine  is  90  per  cent  of  the  indicated  horse-power  of  the  engine. 
About  5  per  cent  is  lost  in  the  transmission  rope,  an  additional  5  per 
cent  in  the  pump  friction,  and  about  8  per  cent  in  the  friction  of  the 
water  in  passing  through  the  pump,  the  energy  actually  delivered  by 
the  pump  being  about  74. 8  per  cent  of  the  indicated  horse-power  of  the 
engine. 

From  this  diagram  it  will  be  noted  that  the  actual  efficiency  of  the 
centrifugal  pump  is  about  88  per  cent  of  the  power  delivered  to  the 
pumps  by  the  rope-drive.  This  is  an  exceedingly  high  record  for  a 
centrifugal  pump,  and  it  is  believed  to  be  the  highest  results  recorded 
for  this  type  of  machinery. 

It  will  be  noted  from,  the  left-hand  diagram  that  5  per  cent  of  the 
calorific  value  of  the  fuel  is  utilized  in  the  indicated  horse-power  of  the 
engine,  while  by  the  right-hand  diagram  about  75  per  cent  of  the  indi- 
cated horse-power  is  utilized  in  the  actual  water  raised.  Thus  in  this 
plant  only  about  3$  per  cent  of  the  calorific  value  of  the  fuel  is  realized 
in  water  pumped.  To  those  who  have  not  before  analyzed  the  losses 
in  power  transmission,  the  amount  utilized  in  this  plant  may  seem 
absurdly  small.  It  is,  however,  exceptionally  large  for  the  type  of 
plant  used.  In  pumping-engines  of  medium  capacity  it  is  seldom  that 
more  than  7  or  8  per  cent  of  the  fuel  is  utilized,  and  in  the  poorer  type 
of  plants  the  utilization  of  less  than  I  per  cent  is  more  often  the  result. 

A  graphical  analysis  of  the  probable  power  losses  in  the  De  Kalb, 
111.,  Electric  Pumping-plant  (see  Fig.  180)  under  domestic  service,  and 


SELECTION  AND   ARRANGEMENT   OF  PUMPING-PLANTS.      $77 

from  the  I.H.P.  of  the  engine,  is  shown  in  Fig.  192.  In  this  plant  the 
power  is  generated  by  the  De  Kalb  Electrical  Company  at  their  central 
station  and  transmitted  as  a  2 20- volt  direct  current  for  a  distance  of 
about  two-thirds  of  a  mile  to  the  city  pumping-station,  where  the  power 


k=  IN  OICATEO    MORSE.  POW&Q. 


FIG.    192.— PROBABLE    EFFICIENCY    DIAGRAM    OF    THE    DE    KALB,    ILL.,  ELECTRIC 
PUMPING-PLANT,  DOMESTIC  SERVICE. 

is  used  for  pumping  in  the  motors  and  pumps  shown  in  Fig.  180. 
From  the  graphical  diagram  it  will  be  noted  that  the  work  delivered  by 
the  pump  is  about  27  per  cent  of  the  I.H.P.  If  the  I.H.P.  is  but  5  per 
cent  of  the  fuel-value,  the  total  plant  efficiency  will  be  1.35  per  cent. 

692.  Considerations  Influencing  the  Selection  and  Arrangement  of 
Pumping-plants. — The  preceding  diagrams,  showing  the  losses  in  energy 


6/8  P  UMPING-MA  CHINER  Y. 

due  to  the  transformation  of  energy  from  coal  burned  to  water  pumped, 
emphasize  the  fact  that  energy  cannot  be  transformed  or  transmitted 
without  loss,  and,  other  things  being  equal,  the  more  directly  energy 
is  utilized,  the  more  economical  the  results  obtained.  Other  factors, 
however,  must  be  considered  in  this  connection.  A  steam  vacuum- 
pump  is  a  more  direct  application  of  steam  than  a  pumping-engine. 
Steam  is,  however,  here  applied  in  a  very  extravagant  manner,  and  the 
vacuum-pump  can  only  be  used  for  emergency  or  occasional  purposes 
where  simplicity  is  of  more  importance  than  economy. 

A  direct-acting  high-pressure  steam-pump  is  a  more  direct  applica- 
tion of  steam  than  the  combination  of  a  steam-engine  and  power-pump. 
Steam,  however,  is  applied  in  this  steam-pump  without  taking  advan- 
tage of  expansion,  and  the  expansive  use  of  steam  in  the  steam-engine 
will  usually  more  than  offset  the  greater  complication  in  the  application 
of  power. 

Other  conditions  also  have  an  important  influence.  When  small 
amounts  of  water  are  to  be  pumped  the  cost  of  attendance  may  more 
than  offset  the  large  energy  losses.  Thus  at  De  Kalb,  111.,  (Fig.  180,) 
it  was  found  that  the  De  Kalb  Electrical  Company,  having  an  electrical 
plant  in  constant  operation,  could  furnish  electric  power  at  less  cost, 
in  spite  of  the  large  transformation  and  transmission  losses  (Fig.  192), 
than  the  cost  at  which  the  city  could  generate  the  power  for  their  own 
plant. 

The  engineer  should,  however,  aim  at  simplicity  in  arrangement 
and  avoid  all  unnecessary  complications.  All  losses  should  be  traced 
and  reduced  to  the  lowest  practicable  amount. 

The  plant  when  selected  should  be  arranged  to  facilitate  its  care 
and  operation,  and  due  regard  should  be  taken  to  foresee  and  provide 
for  future  repairs  and  renewals  with  the  least  possible  expense. 

Fig.  193  shows  the  arrangement  of  a  small  pumping-plant.  The 
plant  is  arranged  for  future  duplication.  The  boiler  is  of  the  internally 
fired  Scotch  marine  type.  No  brick  is  used  for  setting,  but  the  boiler 
is  covered  with  magnesia  sectional  covering  to  prevent  condensation. 
The  coal  is  brought  from  the  coal-room  on  a  car,  being  first  weighed 
so  that  a  systematic  account  of  fuel  used  may  be  kept.  The  boiler  is 
fed  either  by  a  direct-acting  duplex  steam-pump  or  by  an  injector. 
The  feed-water  is  pumped  from  the  main  suction-pipe  through  a  closed 
heater  through  which  the  exhaust  steam  from  the  engine  is  passed. 
All  feed-water  passes  through  a  meter  so  that  a  daily  record  of  evap- 
oration may  be  kept.  A  high-speed  engine  furnishes  power  for 
pumping  by  direct  connection  to  a  triplex  power-pump.  The  steam- 


SELECTION  AND   ARRANGEMENT   OF  PUMPING-PLANTS. 


FIG.  193. — PLAN  AND  ELEVATION  OF  PUMPING-STATION,  SHOWING  BOILER,  POWER- 
PUMP,  AND  DIRECT-CONNECTED  ENGINE. 


680  P  UMPING-MA  CHINER  Y. 

pipe  is  as  direct  as  practicable — enough  angles  being  used  to  allow  for 
expansion.  To  prevent  radiation  and  condensation  the  pipe  is  covered 
in  a  manner  similar  to  the  boiler. 

The  engine-  and  boiler-rooms  should  be  large  enough  to  allow 
plenty  of  room  to  work  around  the  machinery.  They  should  be  well 
lighted  and  reasonably  well  finished.  A  good  building  and  plenty  of 
light  are  great  inducements  to  the  proper  care  of  machinery. 

693.  Capacity  of  Pumping-machinery. — Two  methods  of  pumping 
are  possible  for  water- works  purposes.  One  is  that  of  pumping  into 
some  form  of  storage-reservoir.  The  other  is  that  of  continuous  and 
direct  pumping,  in  which  the  pump  is  operated  at  a  speed  just  sufficient 
to  supply  the  demand  for  water. 

From  what  has  already  been  stated  it  will  be  seen  that  for  water- 
supply  purposes  there  are  great  variations  in  the  demands  for  water 
between  the  maximum  and  minimum  consumption,  and  especially 
between  minimum  consumption  and  fire  service.  A  pumping-plant  for 
water-supply  must  be  equal  to  the  maximum  demands  unless  the 
storage  capacity  is  sufficient  so  that  a  uniform  rate  of  pumping  can  be 
maintained  and  any  unusual  demand  can  be  cared  for  by  the  stored 
supply.  If  the  pumps  are  of  sufficient  capacity  for  maximum  demands, 
their  average  rate  of  work  will  usually  be  very  low,  and  low  efficiency 
will  often  result  (see  Art.  669).  In  pumping  into  a  storage-reservoir, 
the  pumps  can  be  operated  at  their  most  efficient  rate  regardless  of 
consumption,  which  renders  their  operation  much  more  economical. 
The  direct-pressure  system  involves  attendance  night  and  day,  while 
when  pumping  to  a  reservoir,  night  work,  and  consequently  perhaps 
half  the  labor,  can  be  saved  in  small  plants.  In  large  plants  the 
pumps  must  be  run  night  and  day  in  any  event.  The  variation  of 
consumption  in  large  plants  is  comparatively  small,  and  it  does  not 
therefore  greatly  affect  the  economy  of  operation.  The  pumps  can  be 
run  at  or  near  their  most  efficient  rate,  and  for  great  changes  in  con- 
sumption the  variation  in  quantity  can  be  cared  for  by  starting  or 
stopping  some  of  the  reserve  machinery. 

The  quantity  of  water  used  in  different  cities  for  domestic  consump- 
tion varies  in  the  United  States  from  30  to  300  gallons  per  capita, 
according  to  conditions  previously  discussed.  The  quantity  of  water 
which  will  be  needed  at  the  maximum  rate  of  consumption  has  already- 
been  considered.  For  fire  service  the  number  of  fire-streams  which 
should  be  estimated  for  any  community  depends  largely  on  the  character 
and  nature  of  the  community  to  be  protected.  The  formula  of  Mr.  E. 
Kuichling,  Mem.  Am.  Soc.  C.  E.,  for  the  number  of  fire-streams  which 
should  be  provided  for  any  community  is  as  follows: 


THE  SELECTION  OF  SUITABLE  BOILER   CAPACITY.  68 1 

Number  of  streams  =  2.8  \''x\ 

in   which  x  =  the   population   of   the   community  in   thousands    (see 
Chapter  II). 

6p3a.  The  Selection  of  Suitable  Boiler  Capacity. —The  use  of  the 
term  "Boiler  horse-power"  is  somewhat  misleading,  for  the  unit  so 
designated  is  not  necessarily  and  is  in  fact  very  seldom  the  equivalent 
of  the  engine  or  pump  horse-power.  "  Boiler  horse-power  "  as  most 
commonly  understood  means  the  evaporation  of  30  pounds  of  water 
from  a  feed-water  temperature  of  100°  Fahr.  to  steam  at  70  pounds 
pressure.  Ordinarily  it  is  sufficiently  close  to  leave  the  steam  pressure 
out  of  consideration,  although  higher  pressure  would  mean  in  fact 
reduced  evaporation. 

The  boiler  horse-power  required  to  do  a  given  amount  of  useful 
work  in  lifting  water  will  depend  on  the  type  of  pumping  machinery 
adopted.  For  steam  pumping  machinery  and  for  power  pumps  operated 
by  steam-engines  Table  No.  92  gives  the  steam  consumption  per  A.H.P. 
per  hour.  Knowing  the  total  amount  of  power  required,  the  boiler 
horse-power  may  be  found  by  dividing  the  total  steam  consumption 
by  30.  For  example  a  2,ooo,ooo-gallon  (1400  gallons  per  minute) 
compound  direct-acting  steam-pump  pumping  against  a  2OO-foot  head, 
with  a  duty  of  25,000,000  foot-pounds  per  1000  pounds  of  dry  steam, 
will  use  79.2  pounds  of  steam  per  A.H.P.  (see  Table  91).  The 
total  horse-power  is  closely  equal  to  1400  x  200/4000  =  70  (see 
Table  83).  The  boiler  horse-power  required  is  therefore  equal  to 
79.2  x  70/30  =  185  horse-power. 

Where  a  transmission  system  is  in  use  the  various  losses  must  be 
estimated  and  the  I.H.P.  of  the  engine  determined  for  the  A.H.P. 
of  the  water  pumped.  From  Table  No.  89  the  amount  of  steam  used 
by  various  classes  of  steam-engines  can  be  determined  and  the  amount 
of  steam  needed  to  meet  the  various  losses  and  perform  the  work  of 
pumping  can  be  determined  as  before.  For  example,  with  a  compound 
Corliss  engine  direct  connected  to  a  generator,  and  operating  a  motor 
and  pump  two  miles  away,  with  the  quantity  of  water  pumped  and  the 
pressure  as  before,  the  losses  may  be  assumed  as  follows : 

Engine  Friction  8  %,  efficiency  92  per  cent. 
Generator,  "          94    "        " 

Wire  loss  5%,  «         95   « 

Motor,  "         85   "        •« 

Pump,  "          80   "        " 

The  combined  efficiency  will  be  .92  x  -94  X  -95  X  .85  X  .80  = 
.5585  and  to  perform  70  A.H.P.  of  work  will  require  an  engine  of 
70/.  5  58  5  =  125.1  horse-power. 


68  2  PUMPING-MA  CHINER  Y. 

The  steam  consumption  of  a  simple  Corliss  may  be  taken  at  20 
pounds  per  I.H.P.  The  boiler  horse-power  required  will  therefore 
equal  125  X  20/30  =  83.5  horse-power. 

694.  Comparison  of  the  Economy  of  Different  Designs. — The  first  cost 
of  a  pumping-plant,  and  the  fuel  cost,  are  not  the  only  considerations 
in  its  selection.  There  must  also  be  considered  all  other  costs  in  con- 
nection with  the  plant,  including  all  expenses  involved  in  the  original 
installation  and  all  expenses  entailed  in  its  operation  and  maintenance. 
For  example,  one  pumping-plant  may  require  a  more  expensive  foun- 
dation, or  a  larger  building,  and  the  interest  and  sinking  fund  on  such 
additional  cost  may  more  than  offset  any  saving  due  to  higher  duty  or 
greater  efficiency. 

Simplicity  of  arrangement  is  also  very  desirable.  Complication  in 
construction  is  objectionable  because  it  necessarily  entails  greater 
expense  in  repairs  and  maintenance,  and  greater  probability  of  acci- 
dents to  the  installation. 

Pumping- machinery  for  fire  service  and  for  public  water-supplies 
must  be  so  installed  as  to  be  practically  free  from  the  danger  of  a  failure 
in  the  service.  This  is  accomplished  either  by  the  duplication  of  the 
plant  as  a  whole  or  in  part,  or  the  storage  of  water  under  pressure,  or 
often  by  both.  In  important  cases  simplicity  in  design  and  the  conse- 
quent positive  assurance  of  successful  operation  at  all  times  may  out- 
weigh economy  in  operation. 

These  points  cannot  be  given  a  definite  value  or  basis  of  compari- 
son, except  when  all  facts  regarding  the  demands  on  an  installation 
are  known. 

The  comparative  financial  relations  of  various  plants  can  be  made 
on  the  following  basis: 

Interest  on  cost  of  installation $ 

Annual  cost  of  operation : 

Labor .  .    $ 

Fuel 

Oil 

Waste 

Light 

Miscellaneous 

Total . 

Annual  cost  of  maintenance  and  repairs.  ...  

Annual  debit  to  sinking  fund 


Total  relative  cost  of  plant 


COMPARISON  OF  ECONOMY  OF  DIFFERENT  DESIGNS.         683 

695.  Example. — The  following  is  an  example  of  the  application  of 
the  above  principles  to  a  small  pumping-plant  which  was  to  be  installed 
to  replace  a  plant  already  in  use.  The  plant  in  use  consisted  of  two 
double-acting  direct  steam -pumps  raising  water  from  deep  bore-holes 
from  a  depth  of  160  feet  below  the  surface  into  a  reservoir  at  the  sur- 
face. From  this  reservoir  the  water  was  pumped  into  the  water-mains 
against  about  45  pounds  direct  pressure.  It  became  necessary  to 
increase  the  water-supply,  which  was  to  be  secured  from  deep  wells  as 
before.  To  accomplish  this  various  plans  were  investigated. 

The  cost  of  operation  of  the  old  plant  was  excessive.  This  was 
due  to  the  fact  that  the  pumps  used  were  all  extravagant  of  steam,  and 
the  pump  which  was  pumping  into  the  mains  had  to  operate  constantly 
and  at  only  about  one-fifth  its  capacity.  To  reduce  the  cost  of  operation 
a  stand-tower  was  proposed,  and  its  cost  was  included  in  all  estimates 
made.  A  new  deep  well  was  also  included  in  the  cost  of  each  plant. 

The  plans  investigated  were: 

1.  The  enlargement  of  the  old  plant,  including,  besides  the  stand- 
tower  and  deep  well,   a  deep-well  pump  and  a  direct-acting  duplex 
steam-pump. 

2.  The  old  system  enlarged  as  above,  but  substituting  steam-engines 
and  power  deep-well  pumps  for  the  direct-acting  deep-well  pumps. 

3.  Using  deep-well  power-pumps  and  steam-engines,  and  pumping 
directly  into  mains  and  stand-tower  without  using  duplex  steam-pump. 

4.  Substituting  the  air-lift  system  for  the  deep-well  pumps,  the  esti- 
mate to  include  compressor  air-lift  apparatus  and  new  duplex  steam- 
pump. 

5.  Sinking  shaft  150  feet  deep  and  installing  suction-pump  within 
reach  of  the  water  to  force  the  water  directly  into  mains  and  stand- 
pipes.      Estimate  to  include  shaft  and  pump. 

Table  No.  93  gives  the  estimate  of  probable  results  made  on  the 
various  plants  outlined  above. 

From  the  showing  in  the  table  under  a,  b,  and  c,  as  well  as  for 
many  other  reasons,  it  was  decided  that  the  shaft  system  was  the  best 
system  to  adopt. 

Various  classes  of  pumps  could  be  used  with  the  shaft  system. 
Table  No.  93 (d)  gives  an  estimate  of  the  relative  cost  and  economy  of 
various  types. 

This  plant  was  intended  to  have  a  capacity  for  fire  service  of 
1,000,000  gallons  per  day,  but  an  average  of  about  200,000  gallons 
per  day  would  be  used  for  domestic  purposes.  From  the  above  table 
it  will  be  observed  that  at  the  rate  of  pumping  of  200,000  gallons  per 


684 


PUMPING-MA  CHINER  Y. 


TABLE    NO.  93. 

EXAMPLE    OF   A    FINANCIAL    COMPARISON    FOR    A    PUMPING-PLANT. 

(a)     Estimated  Cost  of  Operation  and  Relative  Expense. 


System. 

Engineers 

Repairs. 

Oil. 

Fuel. 

Total. 

Saving 
over  Pres- 
ent Cost. 

$144.0 

$^62 

$30 

$2041 

$0876 

Present  system  enlarged  

I  J.JO 

4OO 

qC 

1  4OO 

^471 

$4OI 

Present     system     with     power 
deep-well  pumps  
Direct  deep-well  pumps  

1440 

Id  4O 

300 

•JCQ 

35 
*?o 

1250 
800 

3025 
262O 

851 
1256 

Air-lift  system   

I44O 

IOO 

2C 

1400 

2o6^ 

Shaft  system  

I4J.O 

IOO 

2? 

COG 

2065 

yii 

1811 

Amount  of  Investment  Warranted  by  Saving  Effected. 


System. 

Estimated 
Cost. 

Cost  of 
Operation. 

Saving 
per  Year. 

Saving  Capitalized  at 

6* 

5% 

$3876 

3475 

3025 
2620 
2965 
2065 

$401 

851 
1256 
911 

1811 

$6683 

14185 
20966 

I5I85 
30183 

$8020 

17020 
25120 
I822O 
36IIO 

$I7OOO 

2OOCO 
2I5OO 
22000 
22000 

Present     system     with     power 

(c)  financial  Comparison. 


System. 

Interest  on 
Cost  of 
Installation 
at  5%. 

Annual  Cost 
of  Operation. 

Annual  Cost 
of  Repairs, 
etc. 

Sinking 
Fund. 

Total  Cost 
per  Annum 

$8<;o 

$007"? 

$4OO 

$IOT5 

$5340 

Present     system     with     power 
deep-well  pumps.  

IOOO 

272s; 

qoo 

1235 

526o 

1075 

2270 

•iCQ 

1275 

4Q7O 

I  IOO 

2865 

IOO 

1325 

53QO 

1250 

1965 

IOO 

1085 

44OO 

(d)   Cost  of  Operating  Various  Types  of  Pumps  for  Shaft  Systems. 


Class  of  Pump. 

Cost. 

Duty, 

looolbs. 
Steam. 

Estimated  Cost  of  Fuel  per  Year  on 
Rates  in  Gallons. 

200,000  Gals. 

500,000  Gals. 

1,000,000  Gals. 

Engine  and  power-pump 
Corliss  geared  pump.  .  . 
High-duty  pump 

Dif. 
$4000 
$2500 
6500 
5500 
I  IOOO 

Int.  on 
Dif.  at 

6*. 
$150 

330 

Lbs. 
50 

75 

IOO 

Dif. 
$350 
$83 
267 
92 
175 

Dif. 
$875 
$208 
667 
230 
437 

Dif. 
$1750 

$415 
1335 
460 

875 

LITER  A  TURE.  68$ 

day  the  difference  in  the  cost  of  fuel  between  pumps  of  types  i  and  2 
is  estimated  at  $83  per  year,  or  less  than  the  interest  on  the  difference 
in  the  cost  between  the  two  engines.  The  cheapest  of  the  above 
pumps  is  therefore  the  most  economical  for  these  conditions.  If  the 
rate  of  pumping  were  500,000  gallons  per  day,  the  second  pump  in  the 
above  table  would  be  most  economical,  and  if  the  rate  were  1,000,000 
gallons,  the  third  and  most  expensive  pump  would  be  best. 

The  various  other  conditions  which  have  heretofore  been  men- 
tioned, and  which  are  often  as  important  as  the  financial  conditions, 
were  carefully  considered.  The  object  was  and  always  should  be  to 
secure  the  best  possible  pumping-plant  after  having  carefully  examined 
the  question  of  safety  and  security  in  construction,  operation,  and 
maintenance,  and  economy  in  the  first  cost,  in  operation  and  in 
maintenance. 

LITERATURE. 

The  following  list  contains  the  titles  of  a  few  of  the  most  useful  books 
and  papers  relating  to  pumping-machinery. 

BOOKS    AND   MONOGRAPHS. 

1.  Colyer.     Pumps  and  Pumping  Machines.     London,  1887. 

2.  Hartman.     Die  Pumpen.     Berlin,  1889. 

3.  Poillon.     Traite  Theoretique  et  Pratique    des    Pompes  et   Machines  d 

clever  les  Eaux.     Paris. 

4.  Barr.     Pumping- machinery.     Philadelphia,  1893. 

5.  Weisbach   &    Herrmann.      Mechanics    of    Pumping-machinery.      New 

York,  1897. 

6.  Davey.     Pumping-machinery.     London,  1900. 

7.  Konig.     Die  Pumpen.     Berlin,  1902. 

8.  Masse.     Les  Pompes.     Paris,  1903. 

9.  Hague.     Pumping  Engines  for  Water-works.     New  York,  1907. 


PERIODICAL     LITERATURE. 

1.  The  Screw  Pumping-engine  of  the  Milwaukee  Flushing-tunnel.      Eng. 

News,  1890,  xxi.  p.  218. 

2.  Dean.     Recent  Practice    in   Pumping-engines.      Jour.  New  Eng.  W.  W. 

Assn.,  1893,  vi.  p.  85. 

3.  Raising  Water  by  the  Air-lift.     Eng.  Record,  1895,  xxxi.  p.  363  et  seq. 

4.  Test  of  the  Detroit  Pumping-engine  (Allis).     Description  of   plant  and 

test.     Eng.  Record,  1895,  xxxn.  p.  477. 

5.  Leavitt.     A  Few  Examples  of  High-grade  Pumping-engines.     Jour.  New 

Eng.  W.  W.  Assn.,  1895,  IX.  p.  163. 

6.  Mead.     The  DeKalb  Electrical  Pumping-plant.     Jour.  Assn.,  Eng.  Soc,, 

1895,  xv.  p.  83. 


686  PUMPING-MACHINERY. 

7.  Mead.    The    Hydraulic   Ram.      Eleventh    Report,  111.    Soc.    Eng.    and 

Surv.,  p.  50. 

8.  Some  Recent  Installations  of  Power-pumps  in  Small  Water-works.      Eng. 

News,  1896,  xxxv.  p.  349. 

9.  Hague.    An  Electrical    Pumping-plant.     Jour.  New   Eng.  W.  W.  Assn., 

1896,  x.  p.  184. 

10.  Johnson.     Limitations  of  the  Air-lift  Pump.     Eng.  News,  1897,  xxxvu. 

p.  250. 

11.  Test  of  Air-lift  at  Rockford,  111.     Eng.  News,  1897,  xxxvii.  p.  140. 

12.  Richards.      The    Design    of  Centrifugal   Pumps.      Eng.    News,    1897, 

xxxvui.  p.  75. 

13.  Johnson.      Deep-well    Pumping.      Jour.    West.    Soc.    Engrs.,    1897,    n. 

p.  169. 

14.  Hood.     Test  of    Pumps    and  Water-lifts.     Water-supply  and  Irrigation 

Paper,  U.  S.  Geol.  Survey,  No.  14,  1898. 

15.  Hague.      Triple-expansion    Engine    at   Ogdensburg,  N.  Y.     Eng.  News, 

1898,  XL.  p.  322. 

16.  Johnson.     A  New  Continuous-flow  Deep-well  Pump.     Eng.  News,  1898, 

xxxix.  p.  34. 

17.  Richards.     Recent   Improvements  in  Centrifugal    Pumps.     Eng.  News, 

1898,  XL.  p.  340. 

1 8.  Marston.     The  Iowa  Agricultural  College  Deep  Well  and  Pump,  Ames, 

la.    Eng.   Record,    1898,  xxxvii.  p.  387.      Efficiencies   of   various 
deep-well  pumps  given. 

19.  Maury.     Supplemental   Pumping-plant   of   the  Peoria  Water  Company, 

Peoria,  111.     Eng.  News,  1898,  xxxix.  p.   19.     Centrifugal  pumps 
operated  by  water-motors. 

20.  Hague.     Pumping-engines  Driven  by  Water-power.     Eng.  News,  1899, 

XLII.  p.  6. 

21.-  Reynolds.  Present  Pumping-engine  Practice  of  the  Edward  P.  Allis  Co. 
Compared  with  that  of  Twenty-five  Years  Ago.  Jour.  New  Eng. 
W.  W.  Assn.,  1899,  xm.  p.  172. 

22.  Coffin.     The  Application  of  Gas-,  Gasoline-,  and  Oil-engines  to  Pump- 

ing-machinery.     Jour.  New  Eng.  W.  W.  Assn.,  1899,  xm.  p.  206  ; 
Eng.  Record,  1899,  xxxix.  p.  79. 

23.  Barrus.     The  Possibilities  of  Economy  in  Pumping-engines.     Jour.  New 

Eng.  W.  W.  Assn.,  1899,  xm.  p.  163. 

24.  A  Gasoline   Pumping-plant   for   the  Water-works  of   Toms  River,  N.  J. 

Eng.  News,  1899,  XLL  P-  I97- 

25.  The  New  Rockford  Pumping-plant.     Eng.  Record,  1899,  xxxix.  p.  352. 

26.  Mead.    The  Mechanics  of  Suction  and  Suction-pipes.     Jour.  West.  Soc. 

Eng.,  1899,  iv.  p.  12. 

27.  Mead.     Deep-well  Pumping-machinery.     Proceedings  Am.  W.  W.  Assn., 

1899. 

28.  Rix.     Pumping  by  Compressed  Air.     Jour.  Assoc.  Eng.  Soc.,  1900,  xxv. 

P-  173- 

29.  Goss.     Test  of  the  Snow  Pumping-engine  at  Indianapolis.     Trans.  Am. 

Soc.  M.  E.,  1900,  xxi,  Paper  No.  854. 

30.  Mead.    The    New  Water-supply  Plant   at   Rockford,  111.     Trans.  Iowa 

Eng.  Soc.,  1901. 

31.  Turbine  Pumping-plants  at  Water-works.    Jour.  Gas  Lgt.,  Aug.  12,,  1902. 


LITER  A  TURE  68  / 

32.  Kiersted.     Comparison  of  Various  Types  of  Pumping  Plants.       Water 

and  Gas  Review,  Nov.  1902. 

33.  Mead.     Some  Small  Water  Works  Pumping  Installations.      Jour.  West. 

Soc.  Engrs.,  1902. 

34.  Harris.     Theory   of   Centrifugal  Pumps  and  Fans.      Trans.  Am.  Soc. 

C.  E.,  Vol.  LI.,  p.  156. 

35.  Torrence.     Management  of   Pumping-stations.      Eng.  Record,  June   20, 

1903. 

36.  Doane.     Past  and    Present  Pumping-methods  in  the  Metropolitan  Dis- 

trict of  Massachusetts.     Eng.  Record,  June  20,  1903. 

37.  Sands.     Some  American  Figures  on  the  Operation  of  Pumping-stations. 

Eng.  Record,  Aug.  6,  1904. 

38.  Whitten.     Some  Recent  Pumping-engine  Tests.      Eng.  News,  May  26, 

1904. 

39.  Kelly.     On  the  Raising  of  Water  by  Compressed  Air,  at  Preesall,  Lan- 

cashire.    Proc.  Inst.  of  Civ.  Engrs.,  No.  3573. 

40.  Air-lift  Pumping-plant  of  the  Redlands  Water  Co.     Eng.  Record,  Jan. 

7,  i905. 

41.  King.    The  Direct  Pumping-method  of  Water-supply  in  Use  at  Taunton, 

Mass.     Jour.  New  Eng.  W.  W.  Assn.,  March,  1905. 

42.  The  New  Lardner's  Point  Pumping-station,  Philadelphia.     Eng.  Record, 

Sept.  1 6,  1905. 

43.  Hill.     The  Selection  of  Water-works  Pumping-machinery.     Eng.  Record, 

July  8,  1905. 

44.  The  Turbine  Pumping-plant  of  the  Buffalo  Water  Works.     Eng.  Record, 

Oct.  28,  1905. 

45.  Mead.     Recent  Improvements  in  the  Plant  of  the  Danville  Water  Com- 

pany.    Jour.  West.  Soc.  Engrs.,  1905. 

46.  Le  Conte  and  Tate.     Mechanical  Tests  of  Pumping  Plants  in  Cal.  U.  S. 

Dept.  Agr.,  Bui.  No.  181. 

47.  Gregory.      Mechanical  Tests  of  Pumping  Plant.      N.  S.  Dept.  Agr.,  BuL 

No.  T83. 

48.  Head.     Comparison  of  the  First  Cost  and  Cost   of  Operation   of  Pump- 

ing Plants  Driven  by  Steam  and  Oil  Engines.     Proc.  Engrs.  Club. 
Phil.,  Oct.  1906. 

49.  Holmes.     Pump  Slippage.     Proc.  Am.  W.  W.  Assn.,  1906. 

50.  Cowan.     Emergency  Air-lift    Equipment  for  Deep  Wells,  Marion  Cityr 

O.     Eng.  News,  Dec.  13,  1906. 

51.  Hague.     The  Growth  of  the  Pumping-station.     Proc.  Am.  W.  W.  Assn., 

1906.     Eng.  News,  July  14,  1906. 

52.  Burdick.     Methods  of  Pumping  Deep  Ground  Waters.     Jour.  West.  Soc. 

Engrs.,  December,  1907. 

53.  Webber.     The  Installation  of  Centrifugal  Pumps.     Eng.  News,  Jan    10, 

1907. 

54.  Reynolds.     High-duty  and    Low-duty  Pumping-machinery.       Proc.  Am. 

W.  W.  Assn.,  1907.     Eng.  Record,  June  22,  1907. 

55.  Doane.     Two-stage  Operation  of  a  Large  Pumping  Engine.     Eng.  Newsy 

Aug.  29,  1907. 

56.  Hawksley  and  Davey.      Comparative  Cost  of   Pumping  by  Steam,  In- 

ternal   Combustion    Engines    and    Electricity,    Based    upon  Actual 
Working.     Eke.  Eng.  (London)  >  June  21,  1907. 


688  PUMPING  MACHINERY. 

57.  Barbour.     Pumping  Water  by  Producer  Gas  Plant  at  St.  Stephen,  N.B. 

Proc.  Am.  W.  W.  Assn.,  1907. 

58.  Tarr.     Greater  Economy  in  Small  Pumping  Plants.     Proc.  Am.  W.  W. 

Assn.,  1907. 

59.  Tipper.     Artesian  Well  Pumping  by  Compressed  Air.     Eng.  News,  Jan. 

16,  1908. 


CHAPTER   XXVII. 
DISTRIBUTING   AND   EQUALIZING    RESERVOIRS. 

696.  Office. — The  forms  of  reservoirs  to  be  here  treated  include  all 
those  which  are  interpolated  at  any  point  in  a  system  between  the 
original  source  and  the  consumer.  The  particular  function  of  these 
reservoirs  differs  considerably  according  to  circumstances,  but  in 
general  they  are  inserted  to  furnish  elasticity  to  the  distributing  system, 
that  is,  to  enable  the  different  portions  to  be  more  or  less  independent 
of  each  other  in  their  operation. 

Such  independence  of  action  is  desirable  from  the  standpoint  of 
economy  and  safety,  and  in  many  cases  is  of  importance  with  respect 
to  the  quality  of  the  water.  For  example,  where  the  water  is  brought 
from  the  source  through  a  long  conduit,  a  distributing  or  equalizing 
reservoir  will  enable  the  conduit  to  be  operated  at  a  comparatively 
uniform  rate  and  hence  to  be  made  of  minimum  size.  Likewise  such 
a  reservoir  will  make  it  possible  to  reduce  the  capacity  of  pumps,  or 
filters,  or  other  similar  works,  and  to  operate  them  more  uniformly  and 
economically ;  or  in  the  case  of  small  works  to  operate  the  pumps  at  full 
capacity  for  a  portion  of  the  day  only.  In  the  case  of  a  ground-water 
supply  a  small  reservoir  will  greatly  increase  the  capacity  of  the  source 
by  making  the  demand  more  uniform.  Again,  in  a  large  distributing 
system,  several  reservoirs  placed  at  different  points  will  effect  con- 
siderable economy  in  the  size  of  the  pipe  system. 

As  a  measure  of  safety  against  the  interruption  of  the  supply  from 
accidents  to  conduit  or  machinery,  distributing-reservoirs  are  of  great 
value ;  or,  looked  at  in  another  way,  additional  safety  against  inter- 
ruption may  often  be  obtained  much  more  cheaply  by  this  means  than 
by  duplication. 

With  respect  to  the  quality  of  the  water  a  reservoir  is  often  of  great 
advantage,  as  pointed  out  in  Art.  463,  by  affording  opportunity  for 
sedimentation  and  also  by  making  it  possible  to  avoid  taking  water 
from  streams  during  periods  of  great  turbidity. 

Small  reservoirs  are  required  also  for  convenience  in  operation,  such 

689 


690  DISTRIBUTING   AND   EQUALIZING   RESERVOIRS. 

as  receiving -reservoirs  at  the  terminals  of  conduits,  small  reservoirs 
for  regulating  the  pressure  at  intermediate  points,  and  similar  reservoirs 
or  air-chambers  at  pumping-stations  for  equalizing  the  action  of  the 
pumps. 

In  all  cases  the  purpose  of  the  reservoirs  here  considered  is  to 
afford  elasticity  of  operation. 

697.  Kinds   of   Reservoirs. — In    discussing    forms    of   construction, 
reservoirs  may  be  classified,  according  to  the  material  employed,  into 
(i)  earthen  reservoirs,  (2)  masonry  reservoirs,  (3)  iron  or  steel  reser- 
voirs,   and    (4)    wooden    reservoirs.      The   first  two    kinds    can    con- 
veniently be  considered  together,  as  the  two  materials  are  very  often 
combined  in  the  same  structure.      The  last  two  will  also  be  treated 
under  the  general  title  of  stand-pipes  and  tanks. 

When  the  reservoir  does  not  need  to  be  elevated  above  the  natural 
surface,  the  most  economical  form,  and  the  usual  one  for  large  capaci- 
ties, is  the  open  reservoir  with  earthen  embankments.  The  storage  of 
surface-waters  in  such  reservoirs  does  not  usually  affect  their  quality, 
especially  if  they  have  previously  been  stored  in  large  impounding- 
reservoirs ;  but  in  the  case  of  ground-waters,  or  filtered  surface-waters, 
it  is  usually  desirable  that  they  be  stored  in  closed  reservoirs.  Such 
reservoirs  are  usually  built  with  masonry  walls  and  covers,  partly  in 
excavation  and  partly  above  the  surface.  If  a  reservoir  requires  to 
be  considerably  elevated,  a  steel  stand-pipe  or  a  tank  of  wood  or  rein- 
forced concrete  is  usually  employed.  A  few  large  reservoirs  have  also 
been  constructed  of  masonry  that  have  extended  to  a  considerable 
height  above  the  ground. 

698.  Capacity. — The  purpose  of  a  reservoir  of  the  kind  here  con- 
sidered being  chiefly  a  matter  of  economy  and  safety,  the  capacity  for 
which  it  should  be  designed  is  not  subject  to  a  rigid  set  of  rules,  but 
depends  entirely  upon  local  circumstances.      It  may  be  wise,  and  good 
economy,  for  one   city  to  have  a  reservoir  capacity  equal  to  8   or   10 
days'  supply,  while  for  a  town  located  on  a  level  plain  it  may  be  best 
to  dispense  with  a  reservoir  and  rely  entirely  upon  reserve  machinery. 
In   determining   the   proper   capacity,   the   cost  of  the  reservoir   must 
therefore  be  balanced  against  the  benefit  derived  therefrom  in  safety 
and  in  the  reduced  expense  for  other  structures  and  reduced  cost  of 
operation . 

This  question  is  conveniently  considered  in  three  parts:  (i)  the 
capacity  necessary  only  to  equalize  the  demand  for  a  single  day;  (2)  a 
capacity  greater  than  this  to  provide  additional  safety  or  economy;  (3) 
a  capacity  less  than  this  where  reservoirs  become  very  expensive. 


CAPACITY   OF  RESERVOIRS.  691 

(1)  In  Chapter  II,  page  30,  are  given  several  curves  showing  the 
hourly  variations  in  consumption  throughout  the  day.      Assuming  the 
supply  uniform,  the  accumulated  deficiency  during  the  hours  when  the 
rate  of  consumption  is  greater  than  an  average  would  be,  for  New  York 
City,  about   1.4  hours'  average  supply;  for  Rochester,  2.5   hours;  for 
Binghamton,  1.8  hours;  for  Des  Moines,  3.7  hours;  for  Rockford,   1.7 
hours;   and  for  Rock  Island,  about   I.I  hours.      The  higher  the  con- 
sumption the  less  the  variation  and  hence  the  less  the  required  storage 
as  measured  by  the  number  of  hours'  average  supply.      To  equalize  the 
demand  on  any  particular  day  will  then  ordinarily  require  a  storage 
capacity  of  from    1.5   to   3  hours'  average  consumption  for  the  day  in 
question,  varying  much  according  to  local  conditions.      Assuming  the 
same  variation  on  the  day  of  maximum  consumption,  and  taking  the 
maximum   daily   consumption   at    1 50   per   cent   of  the    average,    the 
required  storage  to  equalize  the  demand  on  any  day  will  be  equal  to 
1.5  times  the  above  figures,  or  2.2  to  4.5  hours'  consumption  taken  as 
the  yearly  average. 

The  quantity  thus  determined  is  sufficient  only  to  equalize  the 
demand  during  any  single  day,  but  does  not  provide  for  the  variations 
in  daily  consumption.  These  must  be  met  by  varying  the  supply  from 
pumps  or  conduits  or  other  works. 

In  addition  to  the  above  capacity,  the  fire  consumption  for  a  single 
fire  must  be  provided  for.  The  maximum  rate  of  fire  consumption  is 
given  on  page  31.  According  to  Freeman,  a  supply  of  6  hours  for  the 
full  number  of  streams  is  a  sufficient  provision  for  fire.  For  small 
towns  and  villages  3  or  4  hours'  supply  at  the  maximum  rate  would  in 
many  cases  be  ample.  The  amount  required  for  fires  will,  for  exam- 
ple, be  equivalent  to  about  one  day's  consumption  for  a  population  of 
5000,  and  about  6  hours'  consumption  for  a  population  of  100,000, 
assuming  an  average  consumption  of  100  gallons  per  capita. 

The  capacity  as  here  determined  is  the  minimum  desirable,  where 
uniformity  of  operation  is  important  for  at  least  a  day  at  a  time;  as,  for 
example,  for  the  clear- water  reservoir  of  a  filter  system,  or  the  storage- 
reservoir  of  a  ground-water  supply.  It  is  also  the  minimum  desirable 
size  for  the  distributing-reservoir  of  a  gravity  or  a  large  pumping 
system,  and  is  less  than  would  be  used  except  where  the  cost  of  con- 
struction is  very  high.  In  the  case  of  small  towns  where  it  becomes  a 
consideration  to  operate  the  pumps  but  a  portion  of  the  day,  the 
capacity  must  be  made  sufficient  to  furnish  water  during  the  hours  when 
the  pumps  are  idle,  and  in  addition  a  reserve  for  fire  extinguishment. 

(2)  With  a  capacity  equal  to  that  determined  under  (i),  provision 


692  DISTRIBUTING   AND    EQUALIZING    RESERVOIRS. 

for  interruption  of  the  supply  for  repairs  would  have  to  be  made  by  the 
duplication  of  conduits,  by  reserve  pumps,  etc.  The  expense  of  such 
duplication  may,  however,  be  largely  or  wholly  avoided  by  increasing 
the  capacity  of  the  reservoir.  The  best  size  of  a  reservoir  depends  then 
upon  the  time  required  for  repairs,  and  upon  its  cost  as  compared  with 
the  expense  of  duplication.  Where  it  is  possible  to  construct  an  inex- 
pensive open  reservoir  at  a  suitable  elevation  and  in  a  good  location  it 
should  be  given  a  capacity  of  several  days'  supply.  In  practice  the 
capacity  of  such  reservoirs  varies  from  2  or  3  days'  supply  up  to  8  or  10 
days,  and  occasionally  more.  Where  water  is  conveyed  in  a  long 
conduit  the  larger  capacity  is  desirable  in  order  to  avoid  all  danger  of 
interruption  from  accidents.  In  a  purely  pumping  system  a  very  large 
reservoir  is  not  so  necessary,  but  having  it,  the  amount  of  reserve  power 
may  be  reduced  to  a  minimum. 

A  reservoir  of  the  kind  here  considered  may  be  an  elevated  dis- 
tributing-reservoir, or  a  low  receiving-reservoir  from  which  the  water 
may  be  pumped,  according  to  the  local  conditions. 

(3)  Where,  owing  to  the  topography,  it  becomes  necessary  to 
artificially  elevate  a  reservoir  in  the  form  of  a  stand-pipe  or  elevated 
tank,  the  expense  of  construction  becomes  so  great  that  the  economical 
capacity  is  usually  less  than  that  mentioned  under  (i).  The  best 
capacity  in  this  case  depends  much  upon  the  size  of  the  city.  For  large 
cities  it  is  hardly  practicable  to  provide  much  storage  by  means  of 
artificially  elevated  reservoirs,  the  small  stand-pipes  which  are  often 
used  in  such  cases  serving  merely  to  equalize  the  action  of  the  pumps. 
In  large  cities  the  variations  in  demand  occur  more  gradually  than  in 
small  cities;  the  fire  consumption  is  also  of  less  relative  amount,  and 
with  the  large  number  of  pumps  in  use  their  operation  can  be  more 
easily  varied  to  suit  the  consumption.  The  percentage  of  necessary 
reserve  power  is  also  much  less  than  in  small  cities  where  the  number 
of  pumps  is  small. 

In  small  cities  (up  to  a  population  of  50,000  or  more)  it  is  desirable 
to  provide  a  small  storage  even  at  considerable  cost,  as  a  measure  of 
safety  and  economy.  The  fire  rate  is  here  the  principal  consideration, 
and  the  minimum  capacity  should  be  such  as  to  provide  water  at  the 
maximum  fire  rate  for  a  sufficient  length  of  time  to  enable  the  pumping- 
station  to  respond  with  ease  and  certainty.  This  is  ordinarily  taken  as 
about  one  hour.  Beyond  this  it  will  usually  be  desirable  to  add  to  the 
capacity  enough  to  equalize  the  ordinary  flow  over  several  hours  of  the 
day,  or,  in  the  case  of  small  works,  to  enable  the  pumping  to  be  done 
by  operating  a  part  of  the  day  only.  The  capacity  beyond  this  mini- 


LOG  A  TION.  693 

mum  one-hour's  fire  consumption  depends  largely  upon  the  cost  of  the 
tank  and  cost  of  pumping.  If  the  tank  can  be  placed  on  a  natural 
elevation  so  as  to  reduce  the  height  of  construction,  the  capacity  may 
approach  that  mentioned  in  (i)  and  thus  reduce  the  amount  of  reserve 
power  for  fire  purposes  to  a  low  figure.  If  the  ground  is  level,  the  cost 
will  be  high  and  the  capacity  correspondingly  low. 

699.  Location. — The  location  of  an  elevated  reservoir  is  governed 
in  the  first  place  by  the  topography,  and  the  choice  of  location  is  there- 
fore often  very  limited.  In  general  a  distributing-reservoir  should  be 
located  as  centrally  as  possible  with  respect  to  the  district  to  be  served, 
as  this  will  insure  the  most  uniform  and  the  highest  pressures  and  will 
.give  the  smallest  size  of  main  and  branches.  The  best  arrangement  is 
to  have  several  reservoirs  serving  as  many  districts,  but  this  is  seldom 
practicable  except  in  very  large  cities,  the  number  being  usually  limited 
to  one  or  two. 

(a).  The  Single  Reservoir, — In  a  gravity  system  the  conduit  is 
terminated  at  a  reservoir,  and  if  this  reservoir  is  centrally  located  a 
longer  conduit  will  be  required  than  if  it  be  placed  near  one  side  of  the 
system.  A  proper  balance  must  be  struck  between  the  two  extremes. 
In  a  pumping  system  the  pumps  are  usually  located  near  one  side  of  the 
city,  and  the  reservoir  is  placed  either  in  the  vicinity  of  the  pumps  or 
at  a  more  remote  point  in  the  system.  In  the  first  case  all  the  water 
is  usually  passed  through  the  reservoir,  and  the  action  of  the  pumps  is 
very  steady  and  uniform.  In  the  second  case  a  main  usually  leads  to 
the  reservoir  from  some  point  of  the  distributing  system.  The  pumps 
force  water  directly  into  the  system,  and  the  reservoir  takes  only  the 
surplus  at  times  of  low  consumption  and  distributes  it  at  times  of  high 
consumption.  Certain  portions  of  the  area  are  thus  served  direct,  and 
others  are  served  from  the  reservoir.  With  this  arrangement  a  more 

uniform  pressure  will  be  maintained 
in  the  mains,  but  the  operation  of  the 
pumps  will  not  be  as  uniform.  The 
conditions  are  illustrated  diagrammat- 
ically  in  Fig.  194.  Here  P  is  the 
pumping-station,  R  is  the  reservoir, 
and  AB  the  town  to  be  served. 
During  the  night,  water  will  flow  into 

the  reservoir,  and  the  hydraulic  gradient  will  be  the  line  CRy  say. 
During  the  day  when  the  consumption  is  greater  than  the  pumpage  the 
reservoir  will  supply  the  deficiency,  and  water  will  flow  to  some  point 
E  from  both  directions,  giving  a  pressure-line  CDR.  With  the  reser- 


694  DISTRIBUTING   AND    EQUALIZING   RESERVOIRS. 

voir  located  at  C  the  gradient  will  be  a  line  CD',  steeper  than  CD  if 
the  size  of  pipes  remains  the  same.  To  give  as  great  average  pressures 
in  this  case  as  in  the  other  arrangement  will  require  larger  pipes  except 
in  the  immediate  vicinity  of  R. 

($).  Two  or  More  Reservoirs. — Where  two  reservoirs  are  con- 
structed, the  best  arrangement  would  be  to  Aqueduct 
locate  one  near  the  pumps,  or  on  the  side 
of  the  town  where  the  conduit  enters,  and 
the  second  near  the  opposite  side  of  the  sys- 
tem; and  where  several  can  be  built  this 
scheme  can  be  duplicated  if  the  topography 
admits  of  it.  An  instructive  example  of 
such  an  arrangement  is  that  of  the  reser- 
voir system  for  the  supply  from  the  Canal 
de  TOurcq,  Paris,  illustrated  in  Fig.  195.* 
This  arrangement  is  especially  applic-  FIG.  195.  —  RESERVOIR  SYSTEM, 
able  to  a  city  located  in  a  river  valley.  PARIS. 

700.  Elevation. — The  proper  elevation  of  a  reservoir  depends  on  the 
required  pressure  in  the  mains,   a  subject  fully  discussed    in  Chapter 
XXVIII.      Where  more  than  one  zone  of  pressure  is  employed  it  will 
usually  be  possible  to  find  sites  for  reservoirs  to  serve  all  but  the  highest 
zone.      The  latter  may  then  be  operated  without  a  reservoir,  or  with  a 
tank  or  stand-pipe. 

EARTHEN    AND    MASONRY   RESERVOIRS. 

701.  Form  and  Arrangement — Earthen  reservoirs  are  usually  con- 
structed partly  by  excavation  and  partly  by  the  building  up  of  embank- 
ments.      If  masonry  walls  are  used  in  place  of  embankments,  or  as 
interior  linings,  the  reservoir  may  be  called  a  masonry  reservoir. 

When  not  limited  by  other  considerations,  the  location  and  elevation 
of  the  bottom  is  so  chosen  as  to  secure  the  most  economical  relation 
between  excavation  and  filling,  which  relation  depends  much  upon  the 
ease  with  which  material  suitable  for  embankments  can  be  obtained. 
For  single  reservoirs  the  form  most  economical  of  material  is  the  cir- 
cular, but  for  large  reservoirs  the  rectangular  form  is  more  convenient 
to  construct  and  requires  less  land  area,  and  except  when  the  topog- 
raphy favors  an  irregular  outline,  or  where  the  reservoir  is  small,  it  is 
the  form  usually  adopted. 

*  Bechmann,  p.  367. 


EARTHEN  AND    MASONRY  RESERVOIRS.  695 

Where  a  town  is  served  by  a  single  reservoir  it  is  desirable  to  divide 
this  reservoir  into  two  basins  in  order  that  one  basin  may  be  in  use  at 
all  times.  This  is  quite  necessary  where  cleaning  must  be  done  at  fre- 
quent intervals,  and  it  may  be  advisable  in  such  a  case  to  subdivide  the 
reservoir  still  farther,  as  in  the  construction  of  settling-basins. 

For  a  single  rectangular  basin  the  square  is  evidently  the  most 
economical  form.  Where  a  reservoir  is  divided  into  two  or  more  parts 
by  interior  embankments  or  walls,  the  economical  proportions  will  be 
somewhat  different  from  those  suitable  for  a  single  basin.  The  best 
proportions  may  readily  be  determined  by  trial  estimates,  but  where 
the  embankments  are  of  uniform  height  the  general  formula  derived 
in  the  discussion  relating  to  settling-basins  is  applicable.  (See 

Art.  4790 

702.  Depth.  —  The  most  economical  depth  is  again  a  matter  that  is 
in  any  case  easily  determined  by  trial.  It  will,  however,  be  useful  to 
determine  by  analysis  approximately  the  effect  of  various  elements  on 
the  depth.  Assuming  a  reservoir  square  in  plan,  let  x  =  length  of  one 
side  ;  h  =  depth  ;  Q  =  given  capacity  ;  and  c  =  cost  per  unit  area 
of  all  that  portion  whose  cost  is  proportional  to  the  area,  such  as  land, 
reservoir  lining,  cover,  etc.  The  cost  of  wall  or  embankment  will  vary 
approximately  as  Jil,  or  will  be  equal  to  c'k*,  where  c'  is  a  constant. 
The  total  cost  will  then  be 

C  =  4xc'  h?  -^  ex*  ........     (i) 

I~Q 

But  Q  =  hxz,  or  x  =  \J  -r,  whence,  substituting  in  (i),  we  have 


Differentiating  with  respect  to  h,  equating  to  zero,  etc.,  we  find  that 
for  a  minimum  C 


The  economical  depth  is  therefore  proportional  to  the  fifth  root  of  Q, 
and  hence  it  should  vary  but  little  for  considerable  variations  in 

l~xc 

capacity.     Since  Q  —  kx*,  we  have,  from  eq.  (3),  h  =  A/  g-,,  that  is, 

h  is  proportional  to  Vx.  From  eq.  (3)  we  also  see  that  as  the  cost 
per  unit  area  increases  from  any  cause,  h  should  also  increase,  but 
only  in  the  proportion  of  £.  In  practice  the  depths  vary  from  12  to 


696  DISTRIBUTING   AND    EQUALIZING   RESERVOIRS. 

1 8  feet,  for  small  covered  reservoirs  holding  one  million  gallons  or  less, 
to  25,  30,  or  35  feet,  for  open  reservoirs  holding  50  or  100  millions, 
depending  upon  local  circumstances.  With  a  fixed  bottom  elevation 
it  is  to  be  noted  that  the  lift  of  the  pumps  increases  with  increased 
depth,  which  fact  would  tend  to  reduce  the  economical  depth;  also 
that  shallow  reservoirs  give  a  less  variable  pressure  in  the  distributing 
system.  On  the  other  hand  too  shallow  reservoirs  favor  higher  tem- 
peratures and  increased  vegetable  growth,  and  are  thus  disadvantageous. 

703.  Embankment  Construction. — The  construction  of  the  embank- 
ment is  based  on  the  same  principles  as  discussed  in  Chapter  XVI,  but 
the  conditions  are  somewhat  different  from  those  obtaining  with  im- 
pounding-reservoirs.  Distributing-reservoirs  are  relatively  expensive 
structures  and  are  usually  located  in  populous  districts  arid  so  need  to 
be  particularly  impervious.  No  porous  form  of  embankment  is  per- 
missible. In  this  case  also  the  foundation  is  frequently  pervious  and 
the  embankment  cannot  be  connected  with  an  impervious  stratum 
below.  Under  such  conditions  it  is  necessary  to ,  construct  a  water- 
tight lining  over  the  entire  area,  and  to  carefully  connect  it  with  the 
water-tight  portion  of  the  embankment.  Where  a  lining  is  not  neces- 
sary to  secure  imperviousness,  one  is  usually  put  in  to  facilitate  the 
cleaning  of  the  reservoir. 

According  to  circumstances  the  entire  embankment  may  be  imper- 
vious, or  imperviousness  may  be  secured  by  a  puddle  or  concrete  core, 
or  by  a  layer  of  puddle  placed  near  the  face.  The  same  objections  are 
made  to  puddle  cores  as  in  the  case  of  high  embankments,  but  with 
perhaps  less  force.  A  puddle  wall  near  the  face,  Fig.  196,*  is  readily 


FIG.  196. — SECTION  OF  RESERVOIR  EMBANKMENT,   PITTSBURG. 

connected  with  the  bottom  lining,  and  in  this  case  requires  less 
material  than  when  placed  as  a  core  as  in  Fig.  i9/.f  It  gives  a  less 
firm  base  for  the  pavement,  however,  than  coarser  earth,  and  when  the 
water  is  drawn  down  there  is  more  danger  of  slips,  such  as  have 

*  See  Eng.  Record,  1897,  xxxvi.  p.  54. 
f  See  Eng.  News,  1891,  xxxvi.  p.  78. 


LININGS  OF  EARTHEN  RESERVOIRS. 

occurred  in  several  instances.  To  avoid  this,  the  paving  should  be 
placed  on  a  layer  of  broken  stone  and  have  a  good  support  at  the  base, 
somewhat  as  shown  in  the  two  sections  here  illustrated.  To  protect 
the  puddle  from  frost  action  it  is  well  to  place  it  at  some  depth  below 
the  surface  as  in  Fig.  196. 

The  corners  of  all  embankments  should  be  rounded  in  order  to 
admit  of  convenient  working  with  rollers.     If  it  becomes  necessary  to 


" 


FIG.  197.  —  SECTION  OF  RESERVOIR  EMBANKMENT,  BROOKYLN. 

support  the  embankment  on  the  outside  at  any  point  by  a  retaining 
wall,  such  wall  should  be  made  of  a  strength  equivalent  to  the  portion 
of  the  embankment  removed  and  should  not  be  made  impervious. 

704.  Linings  of  Earthen  Reservoirs.  —  The  most  common  form  of 
lining  consists  of  about  ij  to  2  feet  of  puddle  protected  by  a  layer  of 
concrete,  brick,  or  stone  paving,  or  sometimes  only  by  gravel.  On 
the  slopes  the  concrete  is  usually  covered  with  paving  or  replaced 
entirely  by  it,  experience  showing  that  unprotected  concrete  is  apt  to 
be  injured  by  ice.  Various  methods  of  construction  are  illustrated  in 
Chapter  XVI.  Fig.  72,  Art.  388,  illustrates  a  case  where  the  natural 
material  was  impervious  and  a  concrete' floor  was  all  that  was  needed. 
A  layer  of  paving-brick  laid  in  cement  makes  a  good  finish  for  a  con- 
crete lining  which  is  to  be  frequently  exposed. 

Concrete  alone  can  be  made  impervious  by  using  a  rich  mixture  and 
exercising  great  care  in  placing,  or  it  can  be  made  impervious  by  a  coat 
of  cement  plaster.  Practically,  however,  such  imperviousness  is  difficult 
to  secure,  chiefly  because  of  the  shrinkage  cracks  which  are  almost 
certain  to  develop  where  the  exposed  areas  are  large.  To  minimize 
this  difficulty,  concrete  is  often  laid  in  blocks,  with  asphalt  joints 
between.  At  Pittsburg  the  concrete  was  made  in  the  proportions  I,  2, 
and  4,  and  laid  in  blocks  9  inches  thick  and  about  7  feet  square,  with 
V-shaped  joints  of  asphalt  between,  f  inch  wide  at  the  bottom  and 
}  inch  at  the  top.  The  whole  was  laid  on  a  puddle  lining.  The  con- 
crete was  plastered  with  J  inch  of  Portland-cement  mortar,  i  to  I.  A 
similar  process  was  used  at  Minneapolis,  the  concrete  being  laid  in 


698 


DISTRIBUTING  AND  EQUALIZING  RESERVOIRS. 


O    ~* 

5  S 


LININGS  OF  EARTHEN  RESERVOIRS. 


699 


20-foot  squares.  At  the  Albany  filter-beds  the  same  plan  was  used, 
it  being  specified  that  the  asphalt  was  to  remain  soft  at  freezing  tem- 
peratures. In  the  Forbes  Hill  reservoir,  Fig.  198,  the  lining  consists  of 
three  layers:  first  a  layer  of  4  inches  of  concrete,  then  \  inch  of 
cement  plaster  for  imperviousness,  then  4  inches  of  concrete  for  a 
paving,  laid  in  large  blocks.  The  lining  increases  in  thickness  near 
the  top,  as  shown  in  the  figure.  In  some  later  works  the  lining  has 


FIG. 


—  DETAIL  OF  RESERVOIR,  BLOOMINGTON,  ILL. 


been  made  of  two  layers  of  rich  concrete,  each  about  3  inches  thick. 
Each  layer  is  constructed  in  rectangular  blocks,  the  blocks  of  the  upper 
layer  breaking  joints  with  those  below. 

By  the  use  of  reinforced  concrete  a  much  more  nearly  impervious 
floor  can  be  made  without  depending  upon  a  puddle  substratum.  A 
considerable  amount  of  reinforcement  well  distributed  will  limit  the 
cracks  to  very  minute  dimensions  and  will  give  a  practically  impervious 
layer.  The  Bloomington  reservoir,  Fig.  I98a,  is  an  example  of  such 
an  arrangement.  The  bottom  consists  of  a  6-inch  layer  of  concrete 
reinforced  each  way  with  |-inch  rods  spaced  6-inch  centers.  In  the 
Cobb's  Hill  reservoir,  Fig.  I98b,  reinforcement  is  used  only  at  the 
joints  of  the  lower  layer  of  concrete. 

If  ground-water  is  met  with,  which  is  under  considerable  pressi1  ' 


700 


DISTRIBUTING  AND  EQUALIZING  RESERVOIRS. 


it  will  be  necessary,  in  order  to  avoid  rupture  of  the  floor,  to  drain  the 
soil  beneath  the  lining.  In  some  cases  the  ground-water  has  been 
permitted  to  enter  the  reservoir,  when  its  head  exceeds  that  in  the 
reservoir,  through  flap-valves  which  will  close  when  the  difference  of 
head  is  in  the  reverse  direction.  Drainage  of  the  soil  beneath  the 
lining  should  be  done  with  great  caution,  and  especial  care  taken  to 
surround  all  drains  with  gravel  and  sand  so  graded  in  fineness  as 


FIG.  198!}.     COBB'S  HILL  RESERVOIR. 

(From  Engineering  Record t  vol.  LV.) 

effectually  to  prevent  the  washing  out  of  any  of  the  material.     Seepage- 
water  is  also  sometimes  taken  care  of  by  means  of  drains. 

705.  Asphalt  Linings, — Asphalt  is  frequently  used  for  reservoir 
linings  with  good  results.  It  may  be  used  for  the  entire  lining  or  as 
an  intermediate  layer  between  layers  of  concrete.  Used  alone  it  has 
the  advantages  of  greater  elasticity  and  imperviousness  as  compared  to 
concrete.  Another  advantage  in  many  cases  is  its  cheapness.  Its 
chief  disadvantage  is  the  effect  of  the  sun  in  rendering  it  more  or  less 
plastic  and  liable  to  creep  if  used  on  steep  slopes.  Its  durability  in 
water  is  also  not  fully  determined.  Great  care  and  expert  knowledge 
are  required  in  determining  the  proper  proportions  of  the  various 
n*credients  necessary  to  give  good  results. 


ASPHAL T  LININGS.  7OI 

Asphalt  is  applied  either  alone,  or  in  the  form  of  asphaltic  mortar 
or  concrete,  consisting  of  mixtures  of  asphalt  with  sand  or  broken 
stone.  For  rigidity  and  strength  the  broken  stone  mixture  is  to  be 
preferred.  Regarding  the  use  of  asphalt,  the  following  is  quoted  from 
L.  J.  LeConte,  M.  Am.  Soc.  C.  E.,  who  has  had  much  experience  with 
this  material :  * 

"  For  the  bottom  and  side  slopes  natter  than  i£  to  2  the  best  mixture  is 
either  asphalt  mortar  or  asphalt  concrete.  It  is  the  cheapest  and  best  lining, 
and  there  is  no  danger  of  its  crawling  down  the  slopes.  For  steeper  slopes, 
up  to  vertical  faces,  this  kind  of  lining  has  been  tried  and  found  wanting  in 
many  respects.  Under  a  hot  summer  sun  it  will  creep  down  the  faces  in 
spite  of  all  precautions.  Steep  slopes  or  vertical  walls  are  now  coated  as 
follows :  First)  with  a  cold  liquid  asphalt  paint,  which  has  great  penetrating 
and  adhesive  properties  but  is  lacking  in  sun-proof  qualities;  second^  with  a 
heavy  layer  of  ordinary  burlap,  which  is  tightly  stretched  and  pressed  into 
this  liquid  asphalt  paint ;  third,  with  a  heavy  outside  coat  of  hard  asphalt 
paint,  put  on  boiling-hot.  This  constitutes  the  weather  coat,  and  is  hard, 
tough,  and  resists  the  hot  summer  sun  admirably.  Wherever  this  lining  has 
been  used,  no  signs  of  creeping  have  developed  even  on  smooth  vertical  faces. 
Hard  asphalt  paint  is  lacking  in  adhesive  qualities  and  consequently  cannot 
be  placed  directly  on  the  slopes.  The  contract  price  of  this  lining  has  varied 
from  12  to  1 6  cents  per  square  foot,  depending  upon  local  conditions."  The 
second  coating  referred  to  is  usually  laid  at  a  temperature  of  from  300  to  400 
degrees. 

When  the  earth  is  firm  and  compact,  asphalt  linings  can  be  placed 
directly  upon  it,  and  have  frequently  been  so  placed.  Considerable 
settlement  has  in  some  cases  taken  place  without  cracking  the  lining, 
but  this  cannot,  of  course,  be  relied  upon. 

In  relining  the  Queen  Lane  reservoir  at  Philadelphia,  with  the  old 
concrete  lining  left  in  place,  asphalt  concrete  2  inches  thick  was 
used  for  the  floor  and  a  double  layer  of  asphalt  on  the  slopes,  in  a  way 
essentially  similar  to  that  recommended  above,  with  the  exception  that 
a  priming  coat  of  asphalt  dissolved  in  benzine  was  first  applied  to  all 
concrete  surfaces  of  the  old  lining  to  insure  good  adhesion.  The  price 
was  $1.15  per  square  yard  for  the  bottom  and  $1.40  for  the  slopes. 
The  slopes  were  furthermore  lined  with  brick,  laid  flat  in  an  outside 
priming  coat  of  asphalt,  to  give  protection  from  sun  and  ice.  In  the 
new  settling-basins  for  the  Cincinnati  water- works  the  lining  consists 
of  concrete  6  inches,  asphalt  \  inch,  brick  2\  inches.  In  the  Upper 
Belmont  reservoir,  Philadelphia,  the  lining  consists  of  concrete,  finished 
with  a  |-inch  layer  of  asphalt. 

*  Trans.  Am.  Soc.  C.  E.,  1896,  xxxv.  p.  94. 


702  DISTRIBUTING  AND  EQUALIZING  RESERVOIRS. 

A  commendable  design  is  that  of  the  Cobb's  Hill  Reservoir, 
Fig.  ig8b.  Here  the  floor  consists  of  a  6-inch  layer  of  concrete, 
then  a  layer  of  waterproofing  material  consisting  of  five  layers 
of  coal  tar  felt  laid  in  hot  coal  tar  pitch,  and  finally  a  6-inch  layer  of 
concrete  laid  in  blocks  with  joints  filled  with  hot  coal  tar  pitch.  The 
lower  layer  of  concrete  is  reinforced  underneath  the  joints  of  the  upper 
layer. 

706.  Reservoirs  with  Masonry  Walls.  —  These  occupy  less  space  than 
earthen  reservoirs,  but  are  more  expensive  to  construct.  They  are, 
however,  often  the  best  form  for  small  reservoirs  where  space  is  limited, 
and  are  a  suitable  form  in  case  covers  are  required. 

When  the  reservoir  is  excavated  in  firm  earth  or  is  backed  by  a 
well-compacted  embankment,  the  earth  serves  to  support  the  walls 
against  water-pressure.  They  must  then  be  designed  to  sustain  the 
earth-pressure  with  reservoir  empty.  By  adopting  the  circular  form 
the  masonry  will  resist  largely  by  compression  as  a  ring,  and  the 
dimensions  can  be  considerably  reduced  below  those  required  for  a 
wall  resisting  by  gravity  alone.  The  relative  resistance  as  a  ring 
decreases  as  the  square  of  the  radius  increases,  but  for  reservoirs  up  to 
75  or  100  feet  in  diameter  this  element  may  be  largely  relied  upon  for 
support.  Several  small  circular  reservoirs  have  been  built  of  diameters 
of  50  to  75  feet,  with  walls  from  1 6  to  22  inches  in  thickness. 

The  masonry  may  be  of  rubble,  concrete,  or  brick,  according  to  cir- 
cumstances. If  exposed,  a  lining  of  paving-brick  makes  an  excellent 
finish.  It  is  needless  to  say  that  in  all  work  of  this  character  the 
greatest  care  should  be  taken  to  secure  the  best  workmanship,  particu- 
larly in  the  mixing  and  laying  of  concrete  and  the  thorough  filling  of 
masonry  joints  with  mortar,  essentially  as  in  dam  construction. 

Imperviousness  is  usually  secured  in  large  masonry  reservoirs  by  a 
layer  of  puddle  placed  back  of  the  wall  and  thoroughly  rammed,  and 
the  bottom  lining  is  treated  in  a  similar  way.  In  small  reservoirs  more 
reliance  is  placed  upon  impervious  masonry,  made  so  by  an  asphalt 
coating,  or  by  a  coat  of  Portland-cement  mortar,  or  by  the  use  of  rein- 
forced concrete.  In  covered  reservoirs  cracks  are  easier  to  prevent 
than  in  open  reservoirs  as  the  temperature  changes  are  much  more 
moderate. 

Two  modern    examples  of    reservoir  walls  are  illustrated    in  Figs. 

a  and  igSb.  The  former  is  a  reinforced  concrete  wall  forming  part 
)f  a  circular  reservoir  of  300  feet  diameter.  The  wall  is  thoroughly  con- 
i^ted  to  the  floor,  which  is  also  reinforced  so  that  the  entire  structure 
is  a  concrete  monolith.  No  expansion  joints  are  used,  the  circular  form 


ARRANGEMENT  OF  PIPES,   VALVES,  ETC.  703 

being  favorable  to  such  construction.  The  inner  face  of  the  wall  was 
coated  with  a  I  :  I  mixture  of  waterproof  cement  and  the  floor  finished 
with  a  surface  coat  of  i :  i|  mortar.* 

In  the  Cobb's  Hill  reservoir  plain  concrete  is  used  for  the  walls. 
These  are  constructed  in  sections  20  feet  long  and  at  the  joints  a  key- 
way  is  provided  which  is  filled  with  clay  puddle.  A  passageway  for 
inspection  purposes  is  built  in  the  wall,  and  to  assist  in  detecting  leaks 
a  series  of  drain  pipes  are  provided  leading  from  beneath  the  floor  into 
the  pass  age  way.  | 

While  it  is  comparatively  easy  to  secure  imperviousness  at  the  outset 
by  the  use  of  cement,  it  is  difficult  to  prevent  the  formation  of  slight 
cracks.  These  permit  the  water  to  find  its  way  into  the  surrounding 
soil,  and  when  the  reservoir  is  quickly  emptied  this  water  exerts  a  back 
pressure  on  the  walls  and  an  upward  pressure  on  the  floor.  It  is  also 
likely  to  injuriously  affect  the  backing  and  the  foundation.  This  con- 
tingency may  be  provided  against  by  draining  the  backing  outside  and 
near  the  base  of  the  walls,  and  the  ground  beneath  the  floor.  In  some 
large  masonry  reservoirs  constructed  in  France,  a  double  bottom  was 
put  in,  with  a  large  interior  space  from  which  all  seepage  is  removed 
by  drains.  Drains  also  lead  into  these  galleries  from  behind  trie  exterior 
walls.  In  this  way  water  is  prevented  from  soaking  into  and  weakening 
the  foundation  (Fig.  204). 

In  the  case  of  covered  reservoirs,  the  floor  may  be  designed  to  resist 
the  upward  pressure  due  to  ground- water  by  the  use  of  inverted  groined 
arches,  held  down  by  the  piers  supporting  the  roof. 

707.  Arrangement  of  Pipes,  Valves,  etc. — Distributing-reservoirs  are 
usually  provided  with  separate  inlet  and  outlet-pipes,  located  prefer- 
ably on  different  sides  of  the  reservoir  in  order  to  promote  circulation 
of  the  water.  In  earthen  reservoirs  these  are  constructed  in  the  same 
manner  as  described  in  Chapter  XVI.  A  by-pass  should  be  provided 
to  enable  the  reservoir  to  be  cut  out  at  any  time.  The  gate-  or  valve- 
chamber  will  vary  in  design  from  a  single  vault  placed  over  a  gate- 
valve,  to  an  elaborate  structure  provided  with  screens  and  arrangements 
for  drawing  water  from  different  levels,  as  in  the  Syracuse  reservoir 
(page  363),  according  to  the  size  of  reservoir  and  the  necessities  of 
the  case.  To  prevent  flooding  of  the  embankments  from  carelessness 
in  operation,  an  overflow  must  be  provided.  This  is  merely  an  open- 

*  Eng.  Record,  1906,  LIII.  p.  285.  See  description  of  Baden  Reservoir,  St.  Louis, 
in  Eng.  Record,  1905,  LII.  p.  454,  for  example  of  another  type  of  reinforced  concrete 
wall. 

t  Eng.  Record,  1907,  LV.  p,  254. 


704 


DISTRIBUTING  AND  EQUALIZING  RESERVOIRS. 


ended  pipe  or  short  weir,  admitting  water  to  the  gate-chamber  or  to  a 
manhole,  whence  it  is  conducted  away  by  a  drain-pipe  laid  through  the 
embankment.  To  facilitate  draining  and  cleaning,  a  waste-pipe  should 
lead  from  a  low  point  in  the  floor  of  the  reservoir.  These  details  are 
illustrated  in  Figs.  198  and  199  and  in  Figs.  77  to  8 1  of  Chapter  XVI. 


Floating  Tube, 


409.SS 


Hinge  of  floating  Tube. 


6*2$ 


Cross-Section. 


FIG.  199,  —  OUTLET-PIPE  DETAILS,  STEUBENVILLE  RESERVOIR. 

(From  Engineering  Record,  vol.  xxxvui.) 

Where  the  reservoir  serves  merely  as  an  equalizing-reservoir, 
receiving  only  the  surplus  water  from  the  distributing  system,  a  single 
pipe  will  serve  for  both  inlet  and  outlet.  Circulation  of  the  water  can 
be  secured  by  extending  the  pipe  to  the  center,  or  beyond,  and  there 
placing  a  flap-valve  through  which  water  is  admitted  to  the  reservoir. 
A  branch  pipe  opening  near  the  side  of  the  reservoir  can  then  be  made 


COVERED  RESERVOIRS.  705 

to  act  as  an  outlet-pipe  only,  by  the  use  of  a  check-valve  opening  out- 
wards. 

For  reservoirs  serving  partly  or  wholly  as  settling-reservoirs,  the 
adjustable  outlet-pipe  shown  in  Fig.  199  is  advantageous  in  enabling 
the  water  to  be  drawn  off  at  all  times  from  near  the  surface.  The 
pivoted  arm  is  provided  with  a  float  and  screen,  and,  in  some  works, 
provision  is  made  to  draw  it  to  any  desired  depth  by  means  of  a  chain 
and  windlass. 

In  open  masonry  reservoirs  gate-chambers  are  conveniently  built 
in  connection  with  the  reservoir  wall.  In  covered  reservoirs  they  are 
usually  omitted,  the  valves  being  placed  within  the  reservoir  and 
operated  from  a  suitable  platform  or  from  the  outside. 

708.  Covered  Reservoirs.  —  In  Chapter  IX,  Art.  196,  the  effect  of 
storage  on  various  classes  of  waters  was  discussed.     It  was  there  shown 
that  ground-waters  should  be  stored  in  covered  reservoirs,  for  the  reason 
that  such  waters  usually  contain  sufficient  quantities  of  plant-food  to 
promote  a  luxuriant  growth  of  vegetable  organisms  unless  the  light  be 
excluded.     Many  cases  have  arisen  of  bad  tastes  and  odors  due  to  this 
cause  which  have  been  entirely  removed  by  covering  the  reservoir,  but 
the  conditions  are  often  so  favorable  for  the  growth  of  plants  that  con- 
siderable care  must  be  taken  to   exclude  all  light.     Filtered  surface- 
waters  should  also  as  a  rule  be  stored  in  covered  reservoirs,  since  by 
the  process  of  nitration  they  are  rendered  somewhat  similar  in  nature 
to  ground-waters.     Where  reservoirs  are  located  in  the  densely  popu- 
lated portions  of  cities,  covers  are  also  advisable,  in  order  to  exclude 
soot  and  dust.     Distributing-reservoirs  are  almost  universally  covered 
in    European    works,    and    as    the    use  of    filtered   supplies    becomes 
more  general  in   this   country    covered   reservoirs   will    become    more 
common. 

Covers  are  usually  made  of  masonry,  but  wood  has  been  used  in  a 
number  of  cases.  It  is  much  cheaper  than  masonry,  but  is  much  less 
durable  and  does  not  keep  the  water  as  cool  in  summer  or  wholly 
prevent  freezing  in  winter. 

709.  Wooden  Covers.  —  A  wooden  cover  for  a  large  area*  may  con- 
sist simply  in  a  horizontal  floor  of  boards,  supported  by  a  system  of 
joists  and  girders  resting  on  a  series  of  wooden  posts.     No  attempt 
need  be  made  to  exclude  the  rain.     For  small  areas  the  covers  can 
readily  be  made  sloping,  and  this  is  a  preferable  arrangement.     Covers 
for  small   circular   reservoirs  and  large  wells  are   conveniently  made 
conical,  with  the  rafters  resting  against  the  wall  or  supported  on  light 
trusses. 


DISTRIBUTING  AND  EQUALIZING  RESERVOIRS. 


710.  Masonry  Covers.  —  Masonry  covers  are  now  generally  made 
of  concrete,  either  in  the  form  of  groined  arches  of  plain  concrete  or 
flat  slab  and  beam  construction  of  reinforced  concrete.  Piers  are 
spaced  from  10  to  15  feet  apart.  They  were  formerly  made  of  brick, 
but  now  are  generally  made  of  concrete  proportioned  at  -ordinary 
working  stresses.  Above  the  arches,  about  2  feet  of  earth  is  placed 
to  prevent  extreme  variations  of  temperature  and  to  protect  the  masonry, 
and  embankments  are  constructed  against  the  side  walls  to  meet  the 
covering  above.  As  the  loading  is  all  dead  load,  a  low  factor  of  safety 
may  be  employed  and  piers  and  arches  made  relatively  light.  Much  of 
the  older  construction  is  heavier  than  necessary.  Table  No.  94,  by 
Coffin,*  gives  the  dimensions  and  pressures  for  brick  piers  of  several 
covered  reservoirs. 

TABLE  NO.  94. 

DIMENSIONS  OF  AND   PRESSURES   ON  PIERS  OF  COVERED   RESERVOIRS    (COFFIN). 


Reservoir. 

Height. 
Feet. 

Cross 
section. 
Sq.  Feet. 

Area  of 
Tributary 
Roof 
Surface. 
Sq.  Feet. 

Approx. 
Weight 
on  Pier. 
Tons. 

Pressure 
on  Pier. 
Tons  per 
Sq.  Foot. 

Newton 

T  5     {J 

2    78 

n6 

32 

II    C 

Brookline                   

17    ^ 

4OO 

144 

26    S 

6  63 

Franklin     

16  ? 

I    OO 

QO    S 

2O 

20 

\shland  

e   o 

400 

yw  o 
248 

CA 

13  s 

Wellesley 

12    2^ 

4  oo 

106 

t?  T 

12    7£ 

Albany 

**  '*3 

7    SO 

2    78 

187 

J4- 

41 

*•*  •/:> 

14    7? 

Clinton 

7   O 

400 

2IO 

78 

IQ    ?O 

Proposed               

7   O 

2    78 

106 

46 

16  s? 

As  between  the  groined  arch  of  plain  concrete  and  the  flat  rein- 
forced concrete  cover  the  former  is  probably  the  cheaper  for  large 
reservoirs,  as  in  such  a  case  the  construction  and  manipulation  of  forms 
can  be  reduced  to  an  economical  system.  In  modern  designs  groined 
arch  covers  have  been  worked  out  to  very  economical  dimensions,  so 
that  little  gain  can  be  effected  by  the  use  of  reinforcement.  An 
example  of  such  design  is  shown  in  Fig.  200,  representing  a  clear-water 
basin  at  one  of  the  Philadelphia  filtration  plants.  Fig.  201  illustrates 
the  common  type  of  concrete  cover  with  exterior  walls  built  of  the  same 
material.  This  form,  or  the  circular  reservoir,  is  probably  the  most 
economical  type  for  small  capacities.  Fig.  122,  p.  468,  shows  the 


*  From  a  very  complete  paper  on  covered  reservoirs  in  Jour.  Assn.  Eng.  Soc., 
1900,  xxxni.  p.  i. 


COVERED  RESERVOIRS. 


707 


interior  of  a  filter  where  the  groined  concrete  arch  is  used.     Another 
example  of  the  use  of  the  groined  arch  is  in  the  Albany  filter  illustrated 


,4'Sencl  anctGraytl 


Section  through  Crown  of  Ar&h. 


Section  through  Piers. 


FIG.  200.  — CLEAR-WATER  RESERVOIR,  PHILADELPHIA. 

(From  Engineering  Record,  vol.  XLII.) 


on  pages  465  and  477.     Here  the  span  is   12  feet  and  rise  2j  feet. 
Concrete  arches  were  used  with  a  thickness  at  the  crown  of  6  inches. 


EffrthFJII 


w 


.^Can-Bars  •§ 
/  wired  every  > 
Y  &H-inHeigM-   I 
Section 
X-Y. 


-/6'd" 


FIG.  201.  —  FORT  MEAD  RESERVOIR. 

(From  Engineering  News,  vol.   LIV.) 

Fig.  202  is  an  illustration  of  a  modern  design  in  which  the  plain 
concrete  arch  and  invert  is  used  in  connection  with  reinforced  walls. 
Pile  foundations  were  there  necessary.  The  concrete  is  depended  upon 
for  imperviousness,  the  wall  joints  being  made  by  means  of  wide  steel 
plates  or  keys. 

The  stresses  in  groined  arches  are  so  complicated  and  uncertain 
that  an  analysis  based  on  the  assumption  of  simple  arch  action  is  of 
very  little  value.  As  a  matter  of  fact  the  concrete  probably  acts  more 
as  a  cantilever  than  an  arch.  This  was  shown  to  be  the  case  at  the 
Albany  filters,  where  the  arches  actually  opened  at  the  crown  from  the 
effects  of  temperature  changes,  the  concrete  being  so  constructed  as  to 
give  a  line  of  weakness  at  this  point.  The  economical  proportions  can 


708 


DISTRIBUTING  AND  EQUALIZING  RESERVOIRS. 


best  be  determined  by  tests  or  from  actual  experience.  The  dimensions 
shown  in  the  illustrations  have  proven  abundantly  large. 

In  Paris,  Belgrand  has  constructed  covers  of  concrete  groined 
arches  with  a  thickness  of  but  2.8  inches  at  the  crown  for  a  span  of 
13.3  feet,  and  4.4  inches  fora  2O-foot  span.  The  piers  were  from  10 
to  17  feet  high  and  13  to  18  inches  square.* 

Piers  should  be  spread  out  at  the  base  so  as  to  distribute  their  load 
sufficiently  to  avoid  practically  all  settlement,  and  the  floor  should  be 


Section  through  Exferior  Wall 

FIG.  202.  —  RESERVOIR  DETAILS,  NEW  ORLEANS. 


Section  through  Inner  Wall 


well  bonded  thereto.  Where  the  foundation  is  soft,  inverted  groined 
arches  may  be  used,  thus  distributing  the  weight  over  the  entire 
area. 

711.  Exterior  Walls. — Where  vaulted  covers  are  used  the  exterior 
walls  must  of  course  be  designed  with  reference  to  the  arch  thrust.  In 
the  earlier  designs  of  brick  and  stone  masonry  these  walls  were  of 
relatively  heavy  section  having  vertical  inside  and  battered  outside  face, 
but  in  the  more  modern  designs  of  concrete  they  have  been  proportioned 
on  more  economical  lines.  This  point  is  well  shown  in  Fig.  200.  A 
somewhat  extreme  design  of  this  character  is  shown  in  Fig.  203.! 

*  See  analysis  of  stresses  in  Coffin's  paper,  also  in  paper  by  Metcalf  in  Trans. 
Am.  Soc.  C.  E  ,  1900,  XLIII.  p.  37. 

f  Zeit.  Ver.  dt.  Ing.,  1898,  XLII.  p.  1059. 


COST.  709 

Fig.  202  illustrates  the  use  of  reinforced  exterior  and  division  walls 
economically  proportioned.  In  case  the  cover  is  of  reinforced  concrete, 
as  in  Fig.  201,  the  exterior  and  division  walls  are  of  simple  reinforced 
construction  and  are  very  economical. 


FIG.  203.  —  SMALL  RESERVOIR  AT  VIENNA. 

712.  Masonry  Reservoirs  Above  Ground. —  Where  no  suitable  eleva- 
tion can  be  found  for  a  reservoir  of  the  kind  already  considered  it  will 
be  necessary  to  provide  artificially  the  required  elevation.     Ordinarily 
a  small  elevated  tank  is  made  to  suffice,  but  in  the  case  of  large  cities 
served   by   long   conduits   it   is   desirable   to   have   a    larger    storage 
capacity,  and  in  a  few  instances  this  has  been  provided  for  by  large 
masonry  reservoirs.     In  these  reservoirs  the  thickness  of  the  walls  is 
determined  in  the  same  way  as  for  masonry  dams.     Sometimes  earth 
embankments  are  thrown  up  around  the  walls  to  maintain  the  water  at 
a   lower   temperature.     Very   interesting   examples   of   high   masonry 
reservoirs   are  furnished   by  those   of    Paris.       The   most   remarkable 
perhaps  is  the  Montmartre  reservoir,  which  is  four  stories  high,  each  of 
the  upper  three  stories  being  used  for  different  services.     The  lowest 
story  is  for  the  piping  and  for  the  drainage  of  water  which  leaks  through 
the  floor.     Fig.  204  shows  a  section  of  this  reservoir.     Reservoirs  of 
this  class  should  receive  careful  architectural  treatment  and  may  be 
made  fine  monumental  works. 

In  repairing  the  inevitable  cracks  which  appear  in  these  large  reser- 
voirs, the  cracks  are  first  cleaned  out  and  then  vulcanized  rubber  strips 
are  cemented  in  with  rubber  cement,  and  the  whole  is  covered  with 
mortar.* 

713.  Cost.  —  The  cost  of  reservoirs  varies  of  course  greatly  accord- 
ing to  local  conditions,  kind  of  reservoir,  and  capacity.     According  to 
capacity  the  cost  per  unit  will  be  less  the  larger  the  reservoir.     If  in 
eq.  (2),  Art.  702,  we  substitute  the  value  of  h  from  eq.  (3),  we  have 

C  =  constant  X  Q*,  or  the  cost  per  unit  capacity  =  -  =  con'*  *n  •    that 

Q          Q* 

*  Eng.  News,  1895,  xxiv.  p.  419. 


DISTRIBUTING   AND    EQUALIZING   RESERVOIRS* 


is,  the  cost  of  reservoirs  per  million  gallons  will  vary  inversely  approxi- 
mately as  <2*.     Thus  if  a  reservoir  with  a  capacity  of  100  million  gallons 


Longitudinal    SecHon  '  Section  of  South  WbJl 

FlG.    204. — MONTMARTRE    RESERVOIR,    PARIS. 

costs  $3.00  per  thousand  gallons  capacity,  one  of  io  millions,  similarly 
constructed,  will  cost  about  3  X   io*  —  about  $4.75  per  thousand  gal- 
lons; one  of  i   million  capacity  will  cost  $7.50,  etc. 
The  actual  cost  of  several  reservoirs  is  as  follows : 


Place. 

Capacity  in 
Gallons. 

Cost  per 
1000  Gals. 
Capacity. 

Remarks. 

Earthen  reservoirs: 

125  OOO.OOO 

$a     qc 

IO4,OOO,OOO 

7    .    ^7 

Minneapolis    Minn     two   each  

46  ooo  ooo 

4  80 

Cincinnati,  O.,  subsiding  reservoirs 
Covered  masonry  reservoirs  : 

50,000,000 
280  ooo 

3-50 

6.  iO 

Estimated, 
^^ooden  cover. 

320  ooo 

TQ      /l>7 

Franklin    N    H      

C04.  qoO 

1  8  oo 

Brick  arches 

Wellesley    Mass  

600  ooo 

17    "3^ 

Concrete  cover 

Rockford    111   

I  OOO  OOO 

20.  oo 

Monier  construction 

I  2OO,OOO 

22    OO 

Brick  arches 

3  ooo  ooo 

7J..OO 

STAND-PIPES. 


711 


Mr.  Coffin  estimates  the  cost  of  circular  reservoirs  with  concrete 
covers  as  follows  :* 


Capacity. 
Gallons. 

Diameter. 
Feet. 

Depth. 
Feet. 

Cost  per 
1000  Gallons 

Capacity. 

500,000 

75 

16 

15.60 

1,000,000 

98 

18 

12.85 

1,500,000 

"5-5 

19 

II  .70 

2,000,000 

125 

22 

II  .00 

3,000,000 

144 

25 

10.07 

4,000,000 

1  66 

25 

9-47 

5,000,000 

186 

25 

9.12 

His  estimates  for  square  reservoirs  are  about  4  per  cent  higher  than 
the  above  figures. 

STAND-PIPES  AND  ELEVATED  TANKS. 

714.  Where  a  reservoir   requires   to   be  artificially  elevated  it   is 
usually  built  as  a  stand-pipe  —  a  tall  slim  tank  resting  on  the  ground 
—  or  as  an  elevated  tank  of  steel,  wood,  or  reinforced  concrete,  sup- 
ported by  a  suitable  tower.     Such  an  elevated  reservoir  may  or  may  not 
be  enclosed  in  a  covering  of  masonry  or  wood,  according  to  the  necessi- 
ties of  the  case  and  the  notions  of  the  designer. 

Reservoirs  of  this  type  are  relatively  so  expensive  that  a  minimum 
amount  of  storage  capacity  is  usually  provided.  As  shown  in  Art. 
698,  they  may  be  used  in  small  towns  to  enable  the  pumps  to  be  more 
economically  operated,  or  in  larger  towns  to  provide  for  fire  consump- 
tion for  an  hour  or  so,  or  in  large  cities  to  act  merely  as  equalizers  for 
the  pumps.  The  capacities  of  stand-pipes  and  tanks  range  ordinarily 
from  50,000  gallons  up  to  a  maximum  of  about  1,500,000  gallons. 

715.  Location.  —  For  storage  purposes  only,  the  location  would  be 
the  same  as  that  for  any  other  reservoir,  as  discussed  in  Art.  699.     To 
reduce   the   cost,  it   is,  however,  desirable   to   place   the   tank  on   the 
highest  ground  available  if  it  be  within  a  reasonable  distance.      Too 
great  distances  will  be  undesirable  on  account  of  the  cost  of  mains  and 
the  loss  of  head  caused  by  a  long  line  of  pipe.     If  the  stand-pipe  acts 
simply  as  a  pressure-regulator,  it  should  be  located  near  the  pumping- 
station,  or  at  least  at  some  point  on  the  force-main  before  any  con- 
siderable number  of  branches  occur. 

Steel  Stand-pipes. 

7 16.  General  Dimensions.  —  The  useful  capacity  of  a  stand-pipe  is 
only  that  part  of  the  volume  which  is  at  a  sufficient  elevation  to  give 

*  Jour.  New  Eng.  W.  W.  Assn.^  1900,  xiv.  p.  283. 


712  DISTRIBUTING  AND   EQUALIZING   RESERVOIRS. 

the  required  pressure.  All  water  below  this  level  acts  merely  as  a 
support  for  the  portion  above.  There  should  therefore  first  be  deter- 
mined the  lowest  useful  level  of  the  water,  and  the  pipe  should  then  be 
made  of  the  desired  capacity  above  this  plane.  The  ratio  of  height  to 
diameter  should  be  chosen  with  respect  to  the  following  considerations  : 
Cost  of  pipe  and  foundation,  variation  in  water-level,  cost  of  pumping, 
and  practicable  thickness  of  plates. 

If  Q  =  useful  capacity  in  gallons,  H  —  height  of  pipe  in  feet.up  to 
the  lowest  useful  level,  x  =  additional  height  necessary  to  give  the 
desired  capacity  Q,  and  d  =  diameter  of  pipe,  then  Q  =  $.gxd*  and 


xd*  =  —  ,  =  a  constant,  =  K.      The  weight  and  cost  of  the  pipe-shell 
are  nearly  proportional  to  (H  -f-  xf  and  to  d*y  or,  Cost  =  K  '  d^(H  -\-  xf  ; 

but  </2  =  —  ,   whence,    Cost   =  K'K^-       —  ,      Differentiating,  etc., 
x  x 

we  find  that  for  a  minimum  cost,  x  —  H.      That  is,  the  total  height 
should  be  2//,  and  d  =  \  /  -  =-.      This  result  will  of  course  be  modi- 


=  \  / 

V   5- 


fied  by  the  other  considerations  mentioned  above,  but  the  relation 
brought  out  will  aid  in  selecting  the  best  dimensions.  If  H  is  large, 
this  rule  would  be  likely  to  give  such  a  height  as  to  make  the  variations 
in  pressure  too  great  and  also  give  too  heavy  plates  at  the  bottom, 
plates  thicker  than  I  -J  inches  being  undesirable.  A  high  tank  will  also 
increase  the  cost  of  pumping.  On  the  other  hand  a  large  diameter  will 
increase  the  cost  of  foundation.  It  is  on  the  whole  desirable  to  use 
rather  large  diameters.  With  ordinary  values  of  capacity,  and  with  H 
equal  to  50.  to  100  feet,  the  best  value  of  x  will  probably  be  from  £  to 
•J  H.  The  best  proportions  can  readily  be  determined  by  trial  estimates 
of  cost  of  pipe  and  additional  cost  of  pumping  per  foot  in  height,  having 
regard  to  the  limiting  conditions  mentioned  above. 

If  the  entire  volume  can  be  counted  on  as  useful,  then  H  =  O,  and 
the  best  proportions  will  depend  very  largely  upon  cost  of  foundation 
and  cost  of  pumping.  Neglecting  the  last  item,  and  assuming  as  before 
that  the  cost  of  shell  varies  as  x^d*  and  that  the  cost  of  foundation  and 
bottom  plate  is  proportional  to  the  area,  or  to  d2,  it  will  be  found  that 
the  economical  height  is  the  same  for  all  capacities,  and  is  in  the  neigh- 
borhood of  2  5  to  30  feet.  The  cost  of  pumping  additional  height  will 
tend  to  reduce  this  slightly,  while  the  cost  of  the  upper  plates,  whose 
thickness  must  be  much  greater  than  required  for  water-pressure,  will 
tend  to  increase  it,  so  that  for  very  large  pipes,  40  feet  will  be  more 
nearly  the  economical  height. 


S  TA  ND  -PIPES.  7  1  3 

If  a  stand-pipe  is  used  only  as  a  relief  to  the  pumps,  its  diameter 
may  be  made  from  3  to  6  feet.'  A  diameter  of  twice  that  of  the  force- 
main  would  reduce  the  rate  of  variation  of  pressure  on  the  pumps  to 
one-fourth  that  in  the  mains,  which  would  be  sufficient  in  most  cases. 

717.  Forces  and  Stresses.  —  The  forces  to  be  considered  in  the  design 
of  a  stand-pipe  are  the  water-pressure,  the  wind-pressure,  the  weight 
of  the  pipe,  and  the  action  of  ice.  In  what  follows  let  h  =  distance  in 
feet  of  any  point  below  the  top,  d—  diameter  of  pipe  in  feet,  r  = 
radius  in  feet,  and  /  =  thickness  of  shell  in  inches  at  any  given  point. 

The  water-pressure  causes  a  stress  per  vertical  lineal  inch  of  pipe 
equal  to 


.  ..... 

2   X    12 

The  stress  per  square  inch  is 

2.6hd 

S  =   —  —  ..........       (2) 

The  wind-pressure  is  usually  taken  at  40  to  50  pounds  per  square 
foot  on  one-half  the  vertical  projection  of  the  tank.  At  the  higher 
figure  the  bending  moment  in  foot-pounds  at  any  distance  h  below  the 
top,  caused  by  the  wind,  is 

M=  50  x  -  •  X  -  =  12.  s^9  ......     (3) 

This  moment  causes  a  maximum  stress  in  the  shell  of  the  pipe  (the 
extreme  fibre)  equal  to 

My_ 
I  ' 

In  this  casejj/  =  r,  and  /=  \n(rf  —  rf]  =  approximately  n  —  r3, 

(t  in  inches,)  whence,  in  pounds  per  square  inch, 

I        Mr  h* 

I'33"      •      •  •      •      (4) 


12 

and  the  stress  per  lineal  inch  along  a  circumferential  line  will  be  equal 
to 

^=1.335  ............      (5) 

If  W=  weight  of  pipe  in  pounds,  the  stress  per  lineal  inch  due  to 
its  weight  will  be 


12    n  d  d 


7H  DISTRIBUTING   AND  EQUALIZING   RESERVOIRS. 

and  per  square  inch  will  be 

*"  =  '°26dt .•••(/) 

Assuming  the  average  thickness  above  the  point  in  question  to  be  - 

and  adding  15  per  cent  for  laps,  etc.,  the  weight  IV  will  be  approxi- 
mately equal  to  7$dth,  and  hence  s"  =  1.9^,  which  value  will  never 
exceed  a  few  hundred  pounds. 

Besides  the  overturning  effect  of  the  wind  there  is  to  be  considered 
the  collapsing  effect  on  the  empty  pipe,  especially  near  the  top  where  the 
plates  are  thin.  This  cannot  readily  be  computed,  but  must  be  provided 
for  by  an  ample  margin  of  strength  at  the  top  of  the  stand-pipe. 

The  effect  of  ice  action  is  a  very  serious  matter  in  unprotected  stand- 
pipes,  but  is  very  difficult  to  calculate  or  provide  for.  It  may  occur  in 
various  ways.  During  severe  weather  a  heavy  cylinder  of  ice  will  form 
next  to  the  shell.  A  warm  spell  may  cause  this  to  melt  somewhat 
around  the  outside,  and  then  the  water  in  the  annular  space  thus  formed 
may  again  freeze,  causing  a  heavy  bursting  pressure.  Or  the  water 
may  be  drawn  down  a  considerable  distance  after  heavy  ice  is  formed 
so  that  a  thaw  will  allow  the  mass  to  drop,  thus  causing  heavy  water- 
hammer;  or,  after  the  water  is  drawn  down,  the  pipe  may  be  so 
rapidly  refilled  as  to  blow  out  the  ice  cover,  causing  sudden  shocks  and 
stresses.  The  importance  of  this  matter  is  attested  by  the  many  acci- 
dents traceable  to  the  action  of  ice. * 

The  stresses  caused  by  ice  action  can  only  be  provided  for  by  the 
use  of  a  good  quality  of  soft  steel  which  will  allow  of  deformation 
without  injury,  and  by  the  use  of  a  large  factor  of  safety.  It  may  well 
be  questioned,  in  view  of  the  uncertainties  of  the  case,  if  all  metal  tanks 
built  in  cold  climates  should  not  be  encased  in  masonry  or  wood.  The 
construction  of  exposed  metal  tanks  in  cold  climates  would  scarcely 
be  considered  possible  in  the  more  conservative  European  practice. 

718.  Material  Employed. — The  material  used  for  stand-pipes  should 
be  soft,  open-hearth  steel,  of  a  tensile  strength  of  about  54,000  to 
62,000  pounds  per  square  inch.  The  best  practice  nowr  calls  for  a 
grade  corresponding  to  flange  steel,  with  phosphorus  limit  of  about 
.06  per  cent,  an  elongation  of  22  to  25  per  cent,  reduction  of  area  of 
50  per  cent,  and  flat  bending  tests,  both  cold  and  after  heating  and 
quenching.  Many  stand-pipes  were  formerly  constructed  of  cheap  tank- 
steel,  which  is  doubtless  one  of  the  principal  causes  of  the  many  failures. 

*  See  reference  14,  p.  740. 


STAND-PIPES. 


715 


Rivets,  being  hand-driven,  are  preferably  made  of  wrought  iron.     Plates 
thicker  than  J  inch  should  be  drilled. 

719.  Thickness  of  Plates. — The  safe  tensile  stress  on  net  section, 
where  but  little  ice  is  likely  to  form,  maybe  taken  at  about  15,000 
pounds  per  square  inch.  Where  thick  ice  is  to  be  expected  the  work- 
ing stress  should  be  reduced  to  12,000  or  even  10,000  pounds,  to 
provide  for  the  unknown  ice  stresses.  The  vertical  joints  will  usually 
be  so  designed  as  to  have  an  efficiency  of  60  to  70  per  cent.  If 
a  =  safe  stress  on  net  section  and  e  =  efficiency,  then  by  eq.  (2),  page 
713,  the  required  thickness  to  resist  the  water-pressure  will  be 


2.6kd 


ae 


or,  if  a  =  12,000  and  e  =  |,  then,  approximately, 

2.67td 


t  = 


8000 


=  .000325^. 


(8) 


(9) 


The  thickness  near  the  top  should  not  be  less  than  J  inch,  or  for  very 
large  pipes,  T5¥  inch.  Plates  thicker  than  I  inch  or  i-J-  inches  should  be 
avoided. 

The  stresses  due  to  wind  and  weight  need  not  be  considered  here, 
as  they  act  at  right  angles  to  the  stresses  due  to  water-pressure  and  are 
also  much  less  in  amount. 

720.  Riveting. — The  plates  forming  a  stand-pipe  are  usually  of  such 
a  width  as  to  build  5  feet  of  pipe,  and  are  from  8  to  10  feet  long.  Each 
course  is  preferably  made  cylindrical,  and  alternately  an  "  inside  "  and 
an  "outside  "  course. 

The  riveting  of  the  vertical  seams  is  the  most  important  part  of  the 
construction,  as  this  determines  the 
strength  and  economy  of  the  stand-pipe. 
Lap-joints  are  most  commonly  used,  but 
for  thicknesses  exceeding  f  inch,  double- 
butt  strap-joints  are  much  preferable  and 
are  stronger.  The  butt-joint  is  arranged 
as  shown  in  Fig.  205,  thus  avoiding  the 
forging  at  corners  which  is  necessary  with 
lap-joints. 

The    maximum    economy   of  riveting 

would  be  secured  by  selecting  a  diameter  of  rivet  such  that  its  shearing 
strength  would  equal  its  crushing  strength,  but  in  practice  the  diameter 


~j~ooo  oocT'o^oe!  OOOOOOH 

>: 

do 

0  I  0 

&0 

0°!°0 

OGMC^OOO 

2°k?l 

OOOOGOO_ 

716 


DISTRIBUTING   AND   EQUALIZING   RESERVOIRS. 


selected  is  usually  somewhat  less  than  this,  in  order  to  avoid  too  great 
a  pitch  and  too  large  a  rivet.  For  lap-joints  the  diameter  is  made 
equal  to  about  twice  the  plate  thickness,  but  not  less  than  f  inch  nor 
more  than  i-J  or  \\  inches.  For  double-butt  joints  the  diameter  need 
not  be  made  so  great.  With  the  selected  diameter,  the  pitch  is  deter- 
mined by  making  the  tensile  strength  on  net  section  equal  to  the 
shearing  value  of  the  rivets,  using  a  safe  shearing  strength  of  about 
three-fifths  of  that  used  for  the  tensile  strength.  The  efficiency  is  then 
the  ratio  of  safe  stress  on  net  section  to  safe  stress  on  gross  section. 

Joints  are  single-,  double-,  or  triple-riveted,  depending  upon  the 
thickness  of  the  plates  and  the  economy  desired.  The  efficiency  of  a 
joint  increases  with  the  number  of  rows  of  rivets  used,  but  for  any  par- 
ticular style  of  riveting  the  efficiency  decreases  somewhat  as  the  thick- 
ness of  the  plates  increases,  on  account  of  the  limitations  to  the  size  of 
rivets.  It  is  therefore  of  greater  relative  importance  to  use  multiple 
riveting  on  thick  plates  than  on  thin  ones.  In  stand-pipe  construction 
it  is  usual  to  employ  single  riveting  for  the  upper  sections  where  the 
plates  are  not  fully  stressed ;  then  double  riveting  up  to  a  thickness  of 
f-  or  i  inch,  and  triple  riveting  for  I  inch  and  above.  With  a  high 
cost  of  material  it  would  be  economical  to  employ  triple  riveting  for 
thinner  plates. 

Table  No.  95,  from  Johnson's  "  Framed  Structures,"  gives  suitable 

TABLE   NO.    95. 

PROPORTIONS    FOR    RIVETED   JOINTS    FOR    STAND-PIPES. 


Kind  of  Joint  on  Vertical  Seams. 

Thickness  of 
Plate. 

Diameter  of 
Rivet. 

8 

Is; 

•s'SS 

j-.CC 
71  D  0> 

"uu 
£ 

Distance 
between 
Pitch-lines. 

Distance  of 
Pitch-line  from 
Edge  of  Plate. 

Percentage  of 
Total  Strength 
of  Plate  De- 
veloped. 

Inch. 

-L 

Inches. 

6 

Inches. 
r| 

Inches. 

Inches. 

41 

TS 

T& 

j  j. 

[50 

Double-               "  

5 

|^ 

25 

«1 

. 

«i 

¥ 

f 

*¥ 
24 

a 

41 

1 

1 

28 

2S" 
2-L 

X4 

T» 

[60 

« 

? 

7 

l\ 

Z4 

ofi 

A8 
li 

butt 

9 

? 

27 

•?& 

A¥ 

Ts 

Y 

ff 
I 

s 

•f 

ofi 

1S 
T5 

t 

IT 
j 

•2.1 

*s 
2* 

Iff 
T3 

£ 

J 

f 

A¥ 

T» 

¥1 

J 

21 

XT 
» 

Uo 

V 

yi 

*1 

H 

Aff 

li 

21 

TF 
j 

*ff 

T-L 

oi 

Z5 

2i 

•1 

Triple-                       

I 

it 

J8 

»« 
21 

7C 

z^ 

S  TA  ND  -PIPES.  7  1 7 

proportions  for  riveted  joints,  together  with  their  efficiencies,  as  com- 
piled from  the  Watertown  Arsenal  reports. 

Horizontal  joints  are  made  single-riveted  lap-joints,  with  rivet  spac- 
ing of  about  three  diameters.  The  wind-stresses  will  not  require  con- 
sideration unless  the  pipe  is  extraordinarily  tall  and  slim.  They  can  in 
any  case  easily  be  considered  by  the  use  of  eq.  (4).  All  seams  should 
be  thoroughly  calked  with  a  round-nosed  calking-tool,  and  any  leaky 
seams  which  may  exist  when  the  pipe  is  filled  should  be  recalked. 

721.  Bottom  Details. — The  bottom  is  made  of  plates  riveted  up  with 
circular  and   radial  joints,  the  former  being  made  lap-joints  and  the 
latter  butt-joints.      The  thickness   need  be  only  enough  to  permit  of 
good  calking  and  to  be  durable, — about  £  inch.      This  bottom  plate  is 
preferably  connected  to  the  side  plates  by  means  of  a  heavy  angle  on 
the  outside,  or  one  on  both  outside  and  inside  the  tank.      The  riveting 
of  the  side  plates  to  the  bottom  angle  is  referred  to  in  the  next  article. 

In  erection,  the  bottom  is  riveted  up  and  attached  to  the  lower  course 
of  the  side  plates  while  supported  a  short  distance  above  the  foundation. 
The  foundation  is  then  prepared  and  the  bottom  carefully  lowered 
thereon.  To  furnish  an  even  bearing  and  to  level  up  the  foundation, 
a  dry  mixture  of  cement  and  sand  is  often  used,  in  order  to  avoid  any 
trouble  from  setting  before  the  work  is  in  place.  Grout  has  also  been 
used  by  forcing  it  through  holes  in  the  bottom  while  the  latter  is 
supported  about  an  inch  above  the  foundation.  The  holes  are  after- 
wards plugged  up. 

722.  Foundation  and  Anchorage. — The  foundation  should  be  made 
monolithic  and  sufficiently  broad  to  give  such  low  pressures  on  the  soil 
that  there  will  be  practically  no  settlement.      Failures  have  occurred 
due  to  poor  work  in  this  respect.      Wind-pressures  should  be  carefully 
considered.    Concrete  is  a  very  suitable  material  for  foundation  purposes. 

Stand-pipes  must  be  anchored  to  the  foundation  to  prevent  being 
overturned  by  the  wind.  Eq.  (5),  page  713,  gives  the  tensile  stress 
per  lineal  inch,  circumferentially,  at  any  point  in  the  pipe  due  to  wind. 

h* 
It    is  S'  =  1.33-7.      The  effect  of  the  weight  of  the  pipe  in  reducing 

this  need  not  be  considered.  The  stress  on  any  anchor-bolt  will  then 
be  S'p,  where  /  =  distance  in  inches  between  bolts.  If  numerous 
bolts  are  used,  their  size  will  not  be  great,  and  they  may  be  put  through 
the  exterior  bottom  angle  and  the  latter  double-riveted  to  the  pipe.  If 
arranged  in  this  way,  they  should  be  numerous  enough  so  that  the  stress 
in  one  bolt  is  not  greater  than  can  be  transmitted  to  the  lower  plates 
by  four  or  five  rivets,  which  will  limit  the  size  of  bolts  to  about  I J  times 


DISTRIBUTING    AND    EQUALIZING   RESERVOIRS. 


the  diameter  of  the  lower  rivets.      By  spacing  the  bolts  sufficiently  close 

this  arrangement  may  be  followed  in  almost 
any  case.  If  this  method  gives  a  large  number 
of  bolts,  it  will  be  simpler  to  use  fewer  and 
larger  bolts,  in  which  case  they  should  be 
fastened  to  the  stand-pipe  by  long  vertical 
pieces  of  angles,  and  the  bolts  placed  close  to 
the  pipe  as  shown  in  Fig.  206.  The  number 
of  bolts  should  not  be  less  than  six  in  any 
case.  Anchor-bolts  should  extend  well  into 
FIG.  206.  the  masonry  and  be  fastened  to  anchor-plates 

embedded  therein. 

The  method  here  given  for  determining  the  stress  in  anchor-bolts 
is  not  equivalent  to  the  usual  method  of  equating  moments  about  the 
edge  of  the  pipe,  but  gives  larger  values  than  that  method.  It  is  the 
same  as  would  be  used  at  any  other  horizontal  joint  of  the  pipe,  or  at 
any  section  of  a  beam,  and  it  assumes  that  a  tension  will  exist  on  the 
windward  side  before  the  resultant  pressure  reaches  the  outer  edge  of 
the  joint — in  fact  as  soon  as  it  passes  the  edge  of  the  "  middle  third," 
as  is  the  usual  assumption  in  all  masonry  designs. 

With  very  high  pipes,  and  on  soft  soils  requiring  broad  foundations, 
it  may  be  desirable  to  distribute  the  pressure  by  the  use  of  large 
brackets  of  a  triangular  shape,  riveted  to  the  pipe,  at  the  outer  ends  of 
which  the  anchor-bolts  may  be  placed.*  These  bolts  may  be  figured 
in  the  same  way  as  explained  above.  For  very  slender  tanks,  stays  or 
guys  of  wire  are  sometimes  used.  These  should  be  very  taut  so  as 
to  prevent  injurious  deflections. 

723.  Pipes  and  Valves. — Usually  a  single  pipe  serves  both  as  inlet 
and  outlet.  This  passes  through  an  arched  opening  in  the  foundation, 
turns  upwards  and  enters  the  stand-pipe 
at  the  bottom,  and  extends  into  it  a 
foot  or  two.  A  lead  joint  is  usually 
made  in  a  bell  casting  riveted  to  the 
bottom  of  the  pipe  as  shown  in  Fig. 
207.  Another  arrangement  is  shown 
in  Fig.  208,  which  illustrates  the  details 
of  the  bottom  of  the  West  Arling- 
ton stand-pipe,  Baltimore,  Md.,  Mr. 
Nicholas  J.  Hill,  chief  engineer.  The 


inlet-  and  overflow-pipes  are  of  steel. 


FIG.  207. — INLET-PIPE  FOR  STAND- 


PIPE. 


*  See  Johnson's  Framed  Structures,  p.  430. 


STAND-PIPES. 


719 


They  are  riveted  to  steel  flanged  collars  at  the  entrance  to  the  pipe, 
and  to  similar  collars  bolted  to  the  flanges  on  the  cast-iron  elbows 
which  rest  on  the  concrete. 


FIG.  208. — BOTTOM  DETAILS,  WEST  ARLINGTON  STAND-PIPE,  BALTIMORE. 

(From  Engineering  Record,  Vol.  XL.) 


A  drain-pipe  through  which  the  tank  may  be  drained  or  flushed 
should  be  provided.  Such  is  also  shown  in  Fig.  208.  Overflow-pipes 
are  not  usually  provided  for  open  stand-pipes.  If  used,  they  should  be 
placed  on  the  outside,  the  water  reaching  them  from  over  a  broad  weir 
or  through  an  orifice  in  the  side  of  the  tank.  Valves  for  inlet-  and 
drain-pipes  should  be  placed  outside  the  foundations. 

Where  the  fire  pressure  must  be  furnished  for  the  most  part  by 
direct  pressure,  some  convenient  method  of  shutting  off  the  pipe  must 
be  employed,  and  right  here  is  where  the  ordinary  system  is  apt  to  be 
weak  and  out  of  repair.  Several  devices  are  in  use  for  closing  a  valve 
by  electrical  means.  A  simple  form  of  such  device  consists  of  an 
ordinary  gate-valve,  operated  through  suitable  gearing  by  means  of  a 
weight  attached  to  a  drum  which  can  be  released  electrically.  The 


72O  DISTRIBUTING   AND   EQUALIZING   RESERVOIRS. 

valve  is  opened  by  hand.*  Another  general  form  consists  of  a  check- 
valve  arranged  to  be  operated  by  an  hydraulic  piston,  the  water  for 
which  is  supplied  from  the  force-main  and  controlled  by  a  small  valve 
operated  electrically,  t 

Another  simple  form  is  where  an  ordinary  hydraulic  gate-valve  is 
arranged  to  be  operated  by  an  electrical  device.  Other  devices  are 
employed  which  act  automatically  when  the  pressure  or  velocity  of  the 
water  is  increased.  These  are  apt  to  cause  heavy  water-hammer, 
unless  specially  guarded  against  by  the  use  of  a  balanced  valve  or  by 
relief-  valves.  \ 

Whatever  the  device  used,  unless  the  valve  opens  as  well  as  closes 
automatically,  a  by-pass  with  check-valve  should  be  provided  to 
enable  water  to  flow  from  the  stand-pipe  in  case  the  pressure  in  the 
mains  falls  below  that  in  the  stand-pipe. 

High-water  electric  alarms  are  advisable  if  the  pipe  be  at  some  dis- 
tance from  the  pumping-station.  The  pressure  indicated  at  the  station 
is  not  a  certain  guide  if  branch  mains  are  led  off  at  intermediate  points. 
For  encased  pipes  or  tanks  a  simple  float,  arranged  to  close  an  electric 
circuit,  may  be  used.  For  exposed  pipes,  ice  is  likely  to  interfere,  and 
in  this  case  a  pressure-gauge  placed  in  a  vault  and  connected  to  the 
stand-pipe  can  be  arranged  to  give  an  alarm  at  any  desired  pressure. 
For  encased  stand-pipes  the  balanced  float-valve  described  on  page 
452  may  be  used  to  advantage  to  shut  off  the  supply. 

724.  Other  Details. —  Top  Angle. — The  top  should  be  stiffened 
against  collapse  by  a  heavy  angle-iron,  not  less  than  3X5  inches,  and 
two  such  angles  should  be  used  for  large  pipes.  The  effect  of  the  Wind 
on  an  empty  pipe  is  not  only  to  cause  a  pressure  on  the  outside,  but 
to  create  a  partial  vacuum  on  the  inside  near  the  top.  Several 
failures  have  occurred  from  lack  of  strength  at  this  point. 

Roof. — It  is  not  customary  to  roof  stand-pipes,  and  for  a  tall  slim 
pipe  a  roof  would  be  of  little  use  and  no  improvement  to  its  appearance. 
With  large,  low  pipes  a  conical  roof  of  curved  profile  may  well  be 
adopted.  It  affords  considerable  protection  and  improves  the  appear- 
ance of  the  structure.  It  is  usually  made  of  sheet  iron  or  copper,  sup- 
ported on  light  angle-iron  ribs  or  framework. 

Ladder. — A  ladder  should  be  built  on  the  outside  of  the  pipe,  but 
none  on  the  inside ;  and  in  general  there  should  be  no  obstructions  on 
the  inside  where  ice  is  likely  to  form  to  any  extent. 

*  Eng.  News,  1889,  xxn.  p.  291. 

\  Eng.  Record,  1894,  xxix.  p.  339;   1900,  xvn.  p.  177. 

\  See  description  of  automatic  valves  in  Eng.  Record,  1894,  xxix.  p.  339;  Eng. 
News,  xxxi.  pp.  12,  284. 


STAND-PIPES. 


721 


Manhole. — A  manhole  is  sometimes  placed  in  the  lower  course  of 
plates.  If  this  is  done,  care  should  be  taken  to  properly  reinforce  the 
cut  plate.  In  Fig.  209  this  is  accomplished  by  an  angle  and  a  cast- 
steel  frame. 


FIG.  209. — MANHOLE,  WEST  ARLINGTON  STAND-PIPE. 

Ornamentation. — Besides  the  use  of  a  roof  as  noted  above,  the 
monotony  of  a  low  stand-pipe  may  sometimes  be  broken  up  by  a  wind- 
ing staircase.  For  a  very  tall  pipe  little  can  be  done,  perhaps,  to  im- 
prove the  appearance.  The  chief  cause  of  the  ugly  appearance  of  such 
pipes  is  the  lack  of  any  apparent  base.  A  massive  masonry  pedestal 
of  a  height  proportioned  to  that  of  the  tank,  used  in  connection  with 
a  suitable  cornice,  would  improve  the  appearance  considerably.* 

Painting. — Stand-pipes  should  be  well  painted  inside  and  out. 
For  the  interior,  asphalt  is  probably  the  best  material  to  use.  After 
painting  the  interior,  the  pipe  should  be  filled  to  detect  leaks  before 
the  outside  is  coated. 

725.  Encased  Stand-pipes. — A  stand-pipe  is  often  surrounded  with 
a  masonry  shell  in  order  to  furnish  protection  from  cold,  or  to  im- 
prove the  appearance  of  the  structure,  or,  in  the  case  of  slender  pipes 
such  as  are  used  for  pressure-regulators,  to  protect  them  from  wind- 
pressure.  The  masonry  shell  may  be  of  stone  or  brick,  and  is  usu- 
ally built  enough  larger  than  the  pipe  to  permit  of  a  stairway  in  the 
space  between.  For  small  towers  the  walls  can  be  calculated  as  if  the 
structure  were  a  monolith,  according  to  the  principles  applied  to  other 
masonry  structures,  the  wind-pressure  and  the  weight  of  masonry  being 

*  See  illustration  in  Johnson's  Framed  Structures,  p.  433. 


722 


DISTRIBUTING   AND    EQUALIZING   RESERVOIRS. 


the  forces  considered.  The  resulting  walls  will  vary  considerably  in 
thickness  from  top  to  bottom.  They  are  usually  made  from  2\  to  4 
feet  thick  at  the  bottom  and  I J  to  2  feet  at  the  top.  With  pipes  of 
large  diameters  (25  to  40  feet)  the  results  of  analysis  under  the 
assumption  of  a  monolithic  structure  would  give  walls  too  thin  to  be 


FIG.  210. — COMPTON  HILL  WATER-TOWER,  ST.  Louis. 

(From  Engineering  News,  vol.  xxxix.) 

stable  locally,  and  it  cannot  well  be  assumed  that  such  walls  act  as 
monoliths.  Under  such  conditions  it  may  be  best  to  provide  against 
wind-pressure  by  the  tank  anchorage,  and  then  brace  the  walls  against 
the  tank,  as  was  done  at  St.  Charles,  Mo.  In  this  case,  with  a  tank 
25  X  70  feet,  the  walls  were  supported  at  six  points  by  circular  lattice 
girders  2  feet  deep  riveted  to  the  tank.  At  the  same  time  these 
girders  served  to  strengthen  the  tank  against  buckling.  The  walls  were 
from  9  to  13  inches  thick. * 


*  Jour.  Assn.  Eng.  Soc.,  1895,  xiv.  p.  533. 


ELEVATED    TANKS.  723 

IJncased  pipes  must  be  provided  with  overflows,  which  may  be  built 
either  inside  or  outside  the  main  pipe.  For  this  type  of  structure, 
roofs  are  quite  necessary,  and  should  be  carefully  proportioned  with 
respect  to  appearance.  The  masonry  offers  considerable  opportunity 
for  architectural  treatment,  and  this  feature  should  be  referred  to  a 
competent  architect. 

A  small  encased  stand-pipe  built  near  a  pumping-station  is  illus- 
trated in  Fig.  210.  The  stand-pipe  is  provided  with  a  2-foot  overflow- 
pipe  which  is  connected  at  two  points  with  the  main  pipe.  Either 
connection  maybe  used,  "according  to  the  pressure  required.  In  the 
design  of  this  structure  the  architectural  features  were  of  considerable 
importance,  the  tower  being  located  in  a  prominent  place.  The  base 
of  the  tower  is  of  blue  Bedford  stone,  the  sub-tower  of  white  limestone, 
and  the  main  shaft  of  buff  brick,  trimmed  with  granite.  The  roof  is  of 
white  tile.  The  tower  is  lighted  by  electricity. 

Elevated  Tanks. 

726.  Economy  of  Elevated  Tanks.  —  If  the  lower  portion  of  the  water 
in  a  stand-pipe  is  at  too  low  an  elevation  for  useful  pressure,  its  only 
office  is  to  furnish  support  to  the  useful  part  above.     Where  this  useless 
zone  is  of  any  considerable  depth  the  support  can  be  more  cheaply 
furnished  by  a  steel  trestle.     Assuming  the  safe  compressive  stress  in 
the  columns  of  such  a  trestle  to  be  10,000  pounds  per  square  inch,  the 
total  cross-section  of  the  columns  necessary  to  support  a  tank  above 
any  given  plane  will  be  about  one-half  that  of  a  stand-pipe  at  the  same 
elevation.     The  thickness  of  a  stand-pipe  would  also  increase  rapidly 
from  this  point  down,  while  the  column  sections  would  increase  but 
slightly.     The  economy  of  the  trestle  form  is  therefore  very  evident 
where  the  distance  to  the  useful  elevation  is  considerable.     The  cost 
of  piping,  trestle-bracing,  etc.,  would  add  to  the  expense  of  the  tank, 
but  the  foundation  for  a  tank  is  less  expensive  than  that  for  a  stand-pipe. 
Besides  being  cheaper,  a  tank  is  much  less  objectionable  in  appearance 
than  a  stand-pipe,  and  experience  indicates  that  trouble  from  ice  is  less 
likely  to  occur. 

727.  Form  and  Proportions.- —  For  roofed  tanks  a  height  equal  to  the 
diameter  would  not  be  far  from  the  most  economical  proportions,  but 
a  height  somewhat  greater  than  this  will  usually  look  better. 

Formerly  the  bottoms  of  tanks  were  made  horizontal  and  supported 
on  a  system  of  beams,  but  later  designs  use  a  conical  or  a  spherical 
bottom  supported  at  the  periphery  only,  which  is  a  better  and  much 


724  DISTRIBUTING   AND    EQUALIZING   RESERVOIRS. 

cheaper  arrangement.  The  spherical  form  is  the  best,  and  involves  no 
special  difficulty  in  construction.  A  hemispherical  bottom  gives  lower 
stresses  to  be  provided  for  than  the  segmental  form,  but  rather  more 
complex  details  at  the  supports,  so  that  the  latter  may  be  preferred, 
especially  where  the  tank  rests  upon  masonry  walls.  The  hemispheri- 
cal form  has,  however,  been  adopted  as  the  standard  by  at  least  one 
large  construction  firm. 

728.  Stresses  in  Tank, — The  thickness  of  side  plates  is  the  same  as 
for  stand-pipes,  and  the  details  are  similar.  If  the  bottom  is  spherical, 
the  tension  per  lineal  inch  will  be  one-half  that  in  a  cylinder  of  the 
same  radius  and  with  the  same  internal  pressure,  or  by  eq.  (i),  page 
713,  will  equal 

5  =  2.6hr,         . (IO) 

in  which  r  =  radius  of  bottom,  and  h  =  head  of  water  in  feet.  For  a 
hemispherical  bottom,  r  =  — ,  and  hence  the  thickness  of  plates  would 

be  equal  to  one-half  that  of  the  lowest  side  course  (assuming  same 
efficiency  of  joint),  but  should  not  be  less  than  T5B  or  f  inch. 

To  analyze  the  stresses  in  a  conical  bottom  it  will  be  convenient 
to  consider  the  tensile  stresses  along  an  element  of  the  cone,  and  those 
at  right  angles  thereto,  separately. 

Fig.  211  shows  the  portion  of  a  conical  bottom  below  any  section 


FIG.  211. 

Im.  W  is  the  total  weight  of  water  directly  above  the  section, 
together  with  the  small  weight  of  water  and  tank  below,  and  5  is  the 
tensile  stress  per  lineal  inch.  Assuming  no  bending  stresses  to  exist, 
we  have 

5  sin  B  X  12  X  2np  =  Wy 
whence 

W 

S  =  .0132—    —  L,      ....  (n) 

0       sin  0' 


p  sin 


ELEVATED    TANKS. 


725 


in  which  p  is  in  feet.      If  h  =  average  head  of  water  on  this  portion  of 
the  bottom,  we  have  (neglecting  the  weight  of  tank)  W  ==.  62. 
whence 


=  2.6 


pk 


sin  0 
At  the  edge  of  the  tank  5  is  a  maximum  and  is  equal  to  2.6  - 


(12) 

rh 


sin  0' 

For   6  =  30°  this  would  be  the  same  as  the  stress  in  the  lowest  side 
plate  (eq.  (i),  page  713). 


FIG.  212. 

The  tensile  stress  in  a  circumferential  direction  will  now  be  deter- 
mined. Fig.  212  shows  one-half  of  a  horizontal  slice  of  the  bottom, 
one  foot  in  vertical  dimension.  5t  and  52  are  the  stresses  per  lineal 
unit,  acting  in  the  directions  indicated,  and  P  is  the  stress  to  be  deter- 
mined. The  length  AB  =  - — ^,  and  is  the  same  as  the  length  over 
which  P  acts.  The  average  head  is  k,  the  average  radius  is  p,  and 


726  DISTRIBUTING   AND   EQUALIZING   RESERVOIRS, 

the  water-pressure  per  lineal  unit  is  w.  Equating  horizontal  compo- 
nents, we  have,  by  a  summation  similar  to  that  performed  in  getting 
the  bursting  stress  in  a  pipe, 

P  =  Sl  cos  0Pl  —  S2  cos  0p2  +  w  sin  0,;.    .      .      .      (13) 
Equating  vertical  components,  we  have 

5X  sin  8.7pl  —  S2  sin  6np2  =  w  cos  67tp\      .      .      .      (14) 
whence  we  may  write 

cos2  e 

5lCos  BPl-  S.2cos  Op2  =  wp-  — - (15) 


sin  V 


62. 5/£ 
Furthermore,  w  =  — 


sin  6  ' 
Substituting  in  eq.  (13)  from  eqs.  (14)  and  (15),  we  have 


sm  0  .   sm 

The  stress  per  lineal  foot  will  be  P  sin  0,  or,  expressed  in  pounds  per 
lineal  inch,  it  is 

P  sin  0  ph 


This  is  just  twice  the  stress  given  by  eq.  (12),  and  is  greater  than  the 
stress  in  the  lower  side  plates  in  the  ratio  of  I  :  sin  0.  To  avoid  too 
thick  bottom  plates,  therefore,  0  should  not  be  made  small. 

729.  Connection  between  Side  and  Bottom  Plates.  —  With  a  conical  or 
segmental  bottom  the  inclined  pull  per  inch  at  the  line  of  connection 
with  the  side  plates  will  be  given  by  eq.  (i  i).  It  is 

W 
S  =  .0132- 


r  sin  0' 
« 
where  W=  total  weight  of  water  and  of  bottom,  r  —  radius  of  tank, 

and  0  =  angle  of  inclination  with  the  horizontal  of  cone  element,  or  of 
tangent  to  circular  segment  at  outer  edge.  The  bottom  and  sides  are 
connected  by  means  of  a  circular  angle  or  shape  iron,  which  resists  the 
horizontal  component  of  the  force  S,  by  compression  as  a  ring.  The 
compressive  stress  in  this  ring  will  be 

P'  =  125  cos  Or  =  .  1 59^  cot -6/,      ....      (18) 
or  approximately 

P'  =  3i.2kr*  cot  0, (19) 

where  h  —  average  depth  of  water.      This  is  a  very  considerable  stress 


ELEVATED    TANKS. 


727 


and  must  be  provided  for  by  a  sufficient  amount  of  metal,  but  the  metal 
of  the    side    plates   and   of  the  bottom  plates  can  be  counted  on  for 

5  or   6   inches  from    the  angle.      The    hemispherical    bottom   causes 
no  stress  of  this  kind  and  is  in  this  way 

preferable. 

Fig.  213  illustrates  three  simple  ar- 
rangements of  this  detail.  The  bent 
bottom  plate  should  in  the  first  two  cases 
be  supported  close  to  the  line  of  the  FlG-  2I3< 

bend.      For  other  details  see  Figs.  214  and  217. 

730.  The  Tower, — The  tower  consists  of  a  steel  trestle  of  four  to 
eight  legs.      The  material  for  this  may  be  medium  steel,  and  compara- 
tively  high   working  stresses   may  be   used   in   its   design,    since   the 
stresses    are    all    dead-  and   wind-load    stresses.      Four  legs   are   the 
smallest  practicable  number,  but  for  tanks  of  large  diameters  the  use 
of  only  four  legs  brings  very  heavy  local  stresses  on  the  tank  at  the 
points  of  connection.      Six  or  eight  is  a  better  number  and  presents  a 
better  appearance,   but  is  more  expensive.      A  design  in  which  four 
posts  are  used  and  branched  near  the  top  was  employed  by  Johnson 

6  Flad  at  Laredo,  Texas,  and  again  by  Mr.  Flad  at  Murphysboro,  111. 
The  latter  design  is  illustrated  in  Figs.  216  and  217.      This  arrange- 
ment gives  twelve  points  of  support  without  the  use  of  an  expensive 
tower.      The  tank  is  sheathed  with  wood  to  prevent  the  formation  of 
ice. 

The  columns  of  the  tower  may  be  of  channels,  Z  bars,  or  any  con- 
venient form  of  section.  They  are  supported  at  intervals  of  20  to  30 
feet  by  lateral  bracing,  which  also  forms  the  wind-bracing.  This 
bracing  usually  consists  of  horizontal  struts  and  diagonal  tie-rods. 
For  eight  or  more  legs  radial  struts  should  also  be  used  to  give  rigidity 
to  the  tower.  In  high  towers  the  columns  should  preferably  have  a 
broken  outline  for  the  sake  of  appearance,  as  in  Fig.  215,  which  illus- 
trates the  large  tank  at  the  Iowa  Agricultural  College  at  Ames,  Iowa, 
Prof.  A.  Marston,  engineer.  This  was  the  first  tank  in  which  this 
feature  was  carried  out.  The  details  of  this  tank  are  shown  in 
Fig.  214. 

731.  Stresses  in  Tower. — The  stresses  due  to  the  vertical  load  are 
readily  calculated,  and  for  the  four-post  tower  those  due  to  wind  also. 
In  the  six-  or  eight-post  tower  the  wind-stresses  are  not  so  readily 
determined.      The    following    method    was    first    suggested    by    Prof. 
Marston.* 

*  Eng.  News,  1898,  xxxix.  p.  371. 


728 


DISTRIBUTING   AND    EQUALIZING   RESERVOIRS. 


•4'xJxj'T 


Bakony  laid  with 
%*0ak  Floor,  Fastened 
to  Nailing  5trips, 

'  '~ 


FIG.  214.— DETAILS  OF  ELEVATED  TANK  AT  AMES,  IOWA. 

(From  Engineering  News,  vol.  xxxix.) 


FIG.  215. — ELEVATED  TANK,  IOWA  AGRICULTURAL  COLLEGE,  AMES,  IOWA 

729 


ELEVATED    TANKS. 


731 


The  amount  of  wind-pressure  on  the  tank  may  be  assumed  the 
same  as  given  for  stand-pipes.  On  the  tower  a  pressure  of  50  pounds 
per  square  foot  of  all  exposed  areas  may  be  assumed.  As  regards 
wind-stresses  the  tower  may  be  considered  as  a  vertical  cantilever 


Elevation.  .Tank  details. 

FIG.  216.— ELEVATED  TANK,  MURPHYSBORO,  ILL. 

(From  Engineering  Record,  vol.  XLII.) 

beam  anchored  to  the  ground.  Then  if  we  pass  a  horizontal  section 
at  the  top  of  each  story,  cutting  the  posts  only  (between  points  of 
attachment  of  diagonal  bracing),  we  can  get  the  vertical  components 
of  post  stresses  as  in  a  beam  made  up  of  parts.  Thus  in  Fig.  218, 


732 


AND    EQUALIZING   RESERVOIRS. 


representing  such  a  section,  let  A  =  section  of  each  post,  and  r  = 
radius  of  tower.  The  maximum  stress  in  post  a  will  occur  when  the 
wind  blows  at  right  angles  to  axis  Im.  If  M  is  the  wind  moment 
about  the  horizontal  plane  assumed,  the  fibre-stress  in  posts  a  will  be 

,343*  j?f 


313 


Foot  of  Main  Columns./ 

FIG.  217. — DETAILS  OF  ELEVATED  TANK,  MURPHYSBORO,  ILL. 

(From  Engineering  Record,  vol.  XLII.) 


Mr 


=  —=-,  where  /  =  moment  of  inertia  of  the  entire  tower  about  Im,  = 


,  if  we  neglect  the  moment  of  inertia  of  each  column   about  its 
own  axis.      Hence  /=  —  T-,  or  the  total  column  stress  == 


M 


(20) 


M 
The  stress  on  columns  b  =  .7—,  and  on  columns  c,  =  o. 


ELEVATED    TANKS.  733 

In  a  six-post  tower  /  =  3^,  and  the  stress  in  the  most  remote 

post  is  — ,  and  on  each  of  the  others  is . 

$r  2  3r 

By  this  method  the  vertical  components  acting  at  the  top  and 
bottom  of  each  story  at  each  post  can  be  found.  Then  taking  each 
story  separately,  the  stresses  in  the  diagonal  rods  can  be  found  by 
equating  vertical  components  acting  at  top 
and  bottom  of  each  post,  beginning  with 
the  post  a  where  the  stresses  on  the  two 
diagonals  attached  thereto  are  equal.  The 
actual  post  stresses  are  then  found  by  equa- 
ting vertical  components  at  either  top  or 
bottom  joint,  and  finally  the  stresses  in  the 
lateral  struts  are  obtained  by  the  use  of  two  •< 

equations  of  the  components  in  a  horizontal  ^ 

plane  acting  at  a  joint. 

The   wind-stresses    should   be    combined  m 

with  maximum  dead-load  stresses  to  get  the 

maximum  post  compression,  and  with  minimum  dead-load  stresses  to 
get  the  tension  on  the  windward  post  and  the  pull  on  the  anchorage. 

732.  Connection  of  Tower  and  Tank.  —  With  conical  or  segmental 
bottoms  the  lower  side  sheets  are  usually  extended  below  the  bottom 
and  finished  with  two  angles  as  flanges,  which  rest  on  the  tops  of  the 
columns,  as  in  Fig.  213.     With  hemispherical  bottoms  the  extension 
of  the  lower  sheets  is  unnecessary,  as  a  central  connection  can  readily 
be  made  to  the  side  and  bottom  plates  as  shown  in  Fig.  214.     Ample 
stiffness  should  be  provided,  and  sufficient  reinforcement  to  enable  the 
column  load  to  be  safely  distributed  into  the  side  plates.     With  but 
four  posts  the  lower  course  of  side  plates  should  be  thickened.     Lateral 
stiffness  is  secured  by  riveting  to  the  tank,  at  the  level  of  the  post  con- 
nection, a  circular  plate  or  lattice  girder  supported  on  brackets,  and 
which  may  at  the  same  time  serve  as  a  floor  or  support  for  a  balcony. 

733.  Anchorage.  —  Each    column    must    be  well   anchored   to  the 
foundation,  with  a  strength  of  anchorage  equal  to  the  maximum  uplift 
due    to    wind   acting   on    empty  tank.     The  amount  of  this  uplift  is 
computed   as   explained  above.     The  foundation   should  be  rigid,  and 
large  and  heavy  enough  to  serve  as  anchorage  and  to  give  only  safe 
pressure  on  the  ground.     There  should  be  practically  no  settlement, 
as   any  unequal   settlement    will    greatly   change   the  stresses  in  the 
tower. 

734.  Inlet-pipe.  —  The  inlet-pipe  is  usually  made  to  enter  the  tank 


734 


DISTRIBUTING   AND    EQUALIZING   RESERVOIRS. 


at  the  center  of  the  bottom,  and  should  be  provided  with  an  expansion- 
joint.  This  may  consist  of  a  brass-lined  stuffing-box  and  gland  or  a 
joint  similar  to  that  shown  in  Fig.  165,  b,  page  611,  may  be  used  to 
advantage.  In  cold  climates  the  pipe  must  be  protected  by  a  frost- 
casing,  which  is  usually  a  simple  wooden  box  with  one  or  more  air- 
spaces and  perhaps  a  packing  of  some  non-conductive  material.  If 
the  tank  is  encased,  it  will  be  necessary  to  provide  an  overflow-pipe. 

735.  Masonry  Towers. — It  is  the  common  practice  in  Europe  to 
support  the  tank  on  a  masonry  structure,  and  also  to  enclose  it 
with  masonry  or  wood.  This  form  of  construction  readily  lends 
itself  to  effective  architectural  treatment  and  should  be  more  often 
adopted  in  this  country.  The  bottom  details  in  this  case  are  ar- 
ranged as  shown  in  Fig.  213,  the  tank  resting  upon  the  wall.  The 
masonry  or  wood  casing  above  must  then  be  bracketed  out.  To 
economize  in  masonry  a  method  of  construction  devised  by  Engineer 
Intze  has  frequently  been  employed  in  Germany.  This  is  illus- 
trated in  Fig.  219,  which  shows  a  section  of  the  tower  at  Kreuz- 

berg,  Berlin.*     The  tank  has  a  capacity  of 
about  IOO,OOO  gallons. 

736.  Wooden  Tanks.  —Elevated  tanks  of 
wood  are  frequently  used  where  low  first 
cost  is  an  essential  element  and  the  quantity 
to  be  stored  does  not  exceed  50,000  to 
75,000  gallons.  Wooden  tanks  are  cheap, 
and  if  well  built  will  last  fifteen  or  twenty 
years.  The  staves  should  be  of  good  clear 
material  and  should  be  dressed  to  proper 
curvature  on  the  outside.  Hoops  should 
be  relatively  thick  to  resist  corrosion,  and 
should  be  thoroughly  coated  with  asphalt 
or  other  protective  coating,  before  being 
put  in  place.  Lugs  and  fastenings  are  a 
source  of  weakness.  They  should  be  care- 
fully designed  and  of  ample  strength.  The 
support  of  the  floors  must  also  be  well 

FIG.  3I9.-INTZE  TOWER     lo°ked   aften      The   chief  SOUrCe   of  trouble 
AT  KREUZBERG,  BERLIN.       with  wooden   tanks  is  in   the  weakening   of 

the  hoops  by  rusting  from  the  inside.     Galvanizing  is  now  being  tried 
as  a  preventive,  and  may  prove  more  successful  than  coatings  formerly 


*  Zeit.  d.   Ver.  deutsch.  Ing.,  1886,  p.  28. 


STORAGE  OF  WATER  UNDER  PRESSURE.  735 

used.  Several  failures  of  wooden  tanks  have  occurred  by  the  sudden 
bursting  of  the  hoops,  and  it  is  questionable  policy  to  construct  such 
tanks  where  their  failure  is  likely  to  endanger  life,  as  it  is  quite  certain 
that  they  will  not  be  regularly  inspected  as  they  should  be. 

736a.  Tanks  of  Reinforced  Concrete.  —  Reinforced  concrete  has 
been  used  to  a  limited  extent  in  the  construction  of  stand-pipes  and 
tanks.  In  first  cost  they  compare  favorably  with  steel  structures  and 
in  durability  are  superior.  The  design  as  to  strength  is  simple,  steel 
being  used  to  supply  the  entire  tensile  strength  required.  Certain 
practical  difficulties  of  construction  arise,  however,  which  have  not  been 
overcome  with  a  sufficient  degree  of  certainty  to  lead  to  the  general 
adoption  of  this  type  of  structure.  These  relate  to  the  securing  of 
complete  imperviousness  and  a  satisfactory  external  appearance.  It  is 
difficult  to  make  the  body  concrete  impervious  owing  to  the  effect  of 
temperature  changes  and  distortions  due  to  tensile  stresses.  Usually, 
therefore,  imperviousness  is  secured  by  means  of  some  kind  of  water- 
proof coating.  It  is  probable  that  a  reliable  and  satisfactory  method  of 
construction  will  soon  be  developed  which  will  lead  to  the  general  use 
of  reinforced  concrete  for  these  structures.  Figs.  2iga  and  2iQb  illus- 
trate a  design  of  tanks  built  at  Havana,  Cuba,  which  are  very  satis- 
factory in  appearance.  The  details  are  clearly  shown  in  Fig.  2igb. 
Imperviousness  was  secured  by  the  use  of  a  well-mixed  wet  concrete.* 

737.  Storage  of  Water  under  Pressure.  —  In  direct-pressure  systems, 
some  elasticity  is  to  be  desired  to  lessen  the  shock  on  the  pumps  and 
mains  clue  to  sudden  variations  in  the  draught.  The  small  stand-pipe 
used  for  regulating  the  pressure  has  already  been  described.  Another 
means  of  furnishing  a  small  amount  of  elasticity  is  by  means  of  large 
air-chambers  placed  on  the  mains  near  the  pumps.  Such  have  been 
used  in  a  number  of  cases,  f  The  air  can  readily  be  supplied  when 
required  by  means  of  a  small  auxiliary  chamber  placed  below  the  main 
chamber  and  so  connected  that  air  can  be  admitted  to  it  under  no 
pressure ;  then  by  closing  the  inlet  and  opening  the  connection  to  the 
main  tank  the  air  may  be  forced  into  the  latter  by  the  water-pressure 
from  the  force-main. 

In  small  works,  air-chambers  or  their  equivalent  may  also  be  used 
to  provide  a  considerable  storage  of  water  and  thus  avoid  the  use  of 
stand-pipes  or  elevated  tanks.  In  the  design  of  such  storage-tanks 
the  larger  the  proportion  of  air-space  the  less  will  be  the  variation  in 


*  Eng.  News,  1908,  LIX.  p.  471. 

t  See  Eng.  Record,  1^93,  xxvu.  p.  196;  1893,  xxvin.  p.  155  ;  1899,  XL.  p.  55. 


DISTRIBUTING  AND  EQUALIZING  RESERVOIRS. 


water-pressure  as  the  tank  is  emptied.  If  F=  volume  of  tank,  and 
v  =  maximum  volume  of  water  stored,  then  V  —  v  =  minimum  volume 
of  air.  If  the  pressure,  when  containing  the  maximum  volume  of  water, 

be  Pt  then  when  the  tank  is  just  empty  the  pressure  is/  =  P  ( i  — ^ 


FIG.  2i9a.    WATER  TANK,  HAVANA,  CUBA. 

(From  Engineering  News,  vol.  LIX.) 
"V          I 

Thus  if  -—  =  — ,  then  /  —  ?SP,  and  the  variation  in  pressure  is  one- 
third  the  maximum.  The  less  the  desired  variation  in  pressure  the 
greater  must  be  the  tank  capacity  for  a  given  water  capacity.  The 
air  can  be  maintained  in  the  tank  by  the  same  method  as  previously 
explained. 

A  system  of  pressure-storage  having  several  advantages  over  that 
just    described  is  the  Acme  Company's  system,  based  on  patents  of 


STORAGE  OF  WATER  UNDER  PRESSURE 


737 


Wm.  E.  Wortham  and  Oscar  Darling.     In  this  system  the  air  is  stored 
in  a  separate  tank  at  a  higher  pressure  than  is  ordinarily  kept  on  the 


No.  10  Wire  Mesh 


"-•'- 1"  Rods, /O'C.foC. 
Half     Vertical      Section 
A    -    B  . 


Hor.  Section 
E-F. 


Half    Vertical      Section 
B  -  C. 


FIG.  aiQb.     WATER  TANK,  HAVANA,  CUBA. 

(From  Engineering  News,  vol.  LIX.) 

water.  By  reducing-valves  in  the  connecting  pipes,  the  pressure  on 
the  water  may  be  maintained  constant,  or  may  be  increased  in  case  of 
fire.  Air-compressors  must  be  used  here  to  keep  up  the  air-supply. 


738  DISTRIBUTING  AND  EQUALIZING  RESERVOIRS. 

A  number  of  plants  of  this  kind  have  been  installed.  (See  references 
10,  15,  1 8,  page  741.)  The  use  of  a  pressure  storage  system  avoids  all 
trouble  from  ice,  and  for  very  small  quantities  is  cheaper  than  an 
elevated  tank.  A  storage-tank  can  also  be  located  at  the  pumping- 
station  and  the  pressure  easily  controlled.  For  large  quantities  the 
system  would  be  very  expensive. 


LITERATURE. 

OPEN    RESERVOIRS. 

1.  The  Brooklyn  Water-works  Extension.     Eng.  News.,  1891,  xxvi.  p.  74. 

2.  Schuyler.     Use   of   Asphalt  for   Reservoir   Linings.     Trans.   Am.    Soc. 

C.  E.,  1892,  xxvii.  p.  629. 

3.  Payson  Park  Reservoir,  Cambridge,  Mass.    Eng.  Record,   1895,  xxxm. 

P-  25- 

4.  Hill.     The  Water-works  of   Syracuse,  N.  Y.    Trans.  Am.  Soc.  C.  E., 

1895,  xxxiv.  p.  23. 

5.  Stanton.     Suggestions  for  a  New  Method  of  Dam  Building.     Trans.  Am. 

Soc.  C.  E.,  1896,  xxxv.  p.  70.  Valuable  discussion  on  the  use  of 
asphalt. 

6.  Le  Conte.     Asphalt  Linings  for  New  and  Old  Reservoirs.     Proc.  Am. 

W.  W.  Assn.,  1896,  p.  230. 

7.  The  New  Highland  Park  Reservoir,  No.  2,  Pittsburg,  Pa.     Eng.  Record, 

1897,  xxxvi.  p.  54- 

8.  New  Reservoirs  of  the  Minneapolis  Water-works.     Eng.  Record,  1897, 

xxxvi.  p.  312. 

9.  Ely.     The  Queen  Lane  Division  of   the  Water-works  of    Philadelphia. 

Describes  the  relining  of  a  defective  reservoir  with  asphalt.  Proc. 
Eng.  Club.  Phila.,  1897,  xiv.  p.  51.  See  also  Eng.  Record,  1897, 
xxxv.  p.  361,  Eng.  News,  1896.,  xxxiv.  p.  164. 

10.  Special  Features  of  the  Reservoirs  at  Cambridge,  Mass.,  Water-works. 

Eng.  News,  1898,  XL.  p.  324. 

11.  Recent    Reservoir   Linings.     Eng.  Record,   1899,  XL.  p.   77.    Describes 

linings  of  three  reservoirs. 

12.  The  New  Water-works  of  Latrobe,  Pa.     Details  of  reservoir,  etc.    Eng. 

Record,  1900,  XLI.  p.  294. 

13.  Whipple  and  Jackson.    The  Action  of  Water  on  Asphalts.     Paper  before 

the  Brooklyn  Engineers'  Club.    Eng.  News,  1900,  XLIII.  p.  187. 

14.  Hague.     The  New  Water-works  Reservoir  at  Trenton,  N.  J.  Eng.  News, 

1901,  XLV.  p.  437- 

15.  The   Upper   Belmont   Reservoir   at   Philadelphia.     Eng.   Record,   1901, 

XLIII.  p.  501. 

1 6.  Jerome  Park  Reservoir.     Reports  concerning  changes  in  and  methods 

of  doing  work.  See  various  articles  in  Eng.  News  and  Eng.  Record 
of  1902  and  1903. 

17.  Saville.    The  Construction  of  a  Reservoir  and  Stand-pipe  on  Forbes  Hill, 

Quincy,  Mass.  Jour.  N.  Eng.  W.  W.  Assn.,  September,  1902.  Eng. 
News,  1902,  XLVII.  p.  217. 


LITER  A  TURE.  739 

18.  Adolph.     Notes  on  the  Arrangement  of  Reservoirs.     Zeit.  d.  Oest.  Ing. 

u.Arch.  Ver.,  Jan.  30,  1903. 

19.  Jerome  Park  Reservoir  Gatehouses  and  Concrete  Lining.     Eng.  Record, 

1904,  L.  p.  112. 

20.  The  Baden  Reservoir  of  the  St.  Louis  Water-works.     Reinforced  con- 

crete walls.     Eng,  Record,  1905,  LII.  p.  454. 

21.  A  Reinforced   Concrete   Reservoir  at    Bloomington,   111.     Eng.   Record, 

1906,  LIII.  p.  285. 

22.  The  Cobb's  Hill  Reservoir,  Rochester,  N.  Y.     Eng.  Record,  1907,  LV. 

P-  254. 

COVERED   RESERVOIRS. 

1.  Morris.     Covered    Service-reservoirs.     Proc.  Inst.  C.  E.,   1883,  LXXIII. 

p.  i.     Many  reservoirs  described  and  illustrated, 

2.  Covered  Reservoirs  at  Newton,  Mass.     Eng.  Record,  1891,  xxiv.  p.  418. 

3.  The  Covered  Water-works    Reservoir  at   Franklin,  N.  H.     Jour.  New 

Eng.    W.   W.    Assn.,   1892,   vn.    p.   82  ;    Eng.   Nevus,  1892,  xxvn. 
p.  486. 

4.  Ewart.    The  Maligakanda  Service-reservoir,  Columbo.     Proc.  Inst.  C.  E., 

1894,  cxvi.  p.  284.     Repairing  cracks  in  concrete. 

5.  Forbes.    Covered  Reservoir  at  Brookline,  Mass.     Jour.  New  Eng.  W.  W. 

Assn.,  1894,  vin.  p.  113  ;  Eng.  News,  1893,  xxx.  p.  498. 

6.  Dutoit.     Precautions  in  the  Construction  of  Large  Masonry  Reservoirs. 

Annales  des  Fonts  et  Chaussees,  June,   1895  ;    Eng.  News,  1895, 
xxiv.  p.  419. 

7.  Gwinn.     Covering  a  Storage-reservoir  at  Quincy,  111.     Eng.  News,  1898, 

xxxix.  p.  373.     Wooden  cover  used. 

8.  Fuller.       Covered    Reservoirs.      Jour.    Assn.    Eng.    Soc.,    1899,    xxim 

p.  119. 

9.  Williams.     Lining  a  Reservoir  near  Whitby.     Proc.  Inst.  C.  E.,   1899, 

cxxxvu.  p.  357.     Asphalt-concrete  lining. 

10.  Coffin.     Design  of  Covered  Reservoirs.     Jour.  Assn.  Eng.   Soc.,   1899, 

XXIII.  p.   I. 

11.  Allin.     Covered  Reservoirs  at   Pasadena,  Cal.     Eng.  News,  1899,  XLII. 

p.  1 01.     Contains  bibliography  on  covered  reservoirs. 

12.  Metcalf.     The  Groined   Arch   as  a  Covering  for  Reservoirs  and  Sand 

Filters :  its  Strength  and  Volume.     Trans.  Am.   Soc.  C.  E.,   1900, 
XLIII.  p.  37. 

13.  Gregory.     Diagram  for  Determining  the  Volume  of  Semielliptical  Groined- 

arch  Vaulting.     Eng.  News,  1900,  XLIV.  p.  130. 

14.  A  Small  Concrete  and  Expanded-metal  Reservoir.     Eng.  Record,  1900, 

XLII.  p.  366.. 

15.  Shields.     Covered  Reservoirs.     Eng.  News,  1900,  XLIII.  p.  70.     Descrip- 

tion of  two  reservoirs. 

1 6.  Ingham.     Open    and    Covered    Service-reservoirs.    Jour.  Gas  Lgt.,  July 

30,  1901. 

17.  A  Concrete  Steel  Reservoir  for  East  Orange,  N.  J.     Ordinary  buttress 

walls  with  slab  and  beam  roof.     Eng.  Record,  1904,  XLIX.  p.  386. 

1 8.  Lea.     The  Construction  of  a  Reinforced   Concrete   Reservoir  at   Fort 

Meade,  South  Dakota.     Eng.  News,  1905,  LIV.  p.  680;  Eng.  Record% 
1906,  LIII.  p.  153. 


74O  DISTRIBUTING  AND  EQUALIZING  RESERVOIRS. 


STAND-PIPES. 

1.  Kiersted.    Stand-pipes0    Paper  at  the  Rensselaer  Poly.  Inst.     Eng.  Record, 

1891,  xxiii.  p.  343. 

2.  The  Des  Moines,  Iowa,  Stand-pipe,     Eng.  News,  1892,  xxvu.  p.  346. 

3.  Stand-pipe  at  Roland  Park,  Baltimore.     Eng.  Record,  1892,  xxvi.  p.  232. 

4.  The  High-service  Water-tower  at  Yonkers,  New  York.    Masonry-enclosed. 

Eng.  News,  1892,  XXVIL  p.  494. 

5.  Coffin,  F.  C.     Stand-pipes  and  their  Design.     Jour.  New  Eng.  W.  W. 

Assn.,  1893,  vin.  p.  202  ;  Eng.  News,  1893,  xxix.  p.  242. 

6.  A  High-  and  Low-service  Stand-pipe  at  Atlantic  City,  N.  J.     Eng.  News, 

1893,  xxx.  p.  188. 

7.  Coffin,  W.  C.     The  Construction  of  Iron  and  Steel  Water-tanks.     Paper 

before  Eng.  Soc.  Western  Pa.     Eng.  Record,  1893,  xxvni.  p.  139. 
S.    The    Prospect    Park    Stand-pipe,    Brooklyn.      Masonry-enclosed.      Eng. 

Record,  1893,  xxvm.  p.  380. 

p.  The  Norwood,  Ohio,  Water-tower.  Eng.  Record,  1894,  xxx.  p.  253. 
10.  Stand-pipe  at  Chevy  Chase,  Neb.  Eng.  Record,  1895,  xxxn.  p.  298. 
IT.  Flad.  On  Encased  Pipe  with  Special  Provision  for  Wind-pressure. 

Jour.  Assn.  Eng.  Soc.,  1895,  xiv.  p.  533. 

12.  The    Washburn    Park    Water-works,    Minneapolis.      Masonry-encased 

stand-pipe.     Eng.  Record,  1895,  xxxn.  p.  259. 

13.  Murphy.     A  Mathematical  Investigation  of  Stand-pipe  Failures.     Eng. 

News,  1894,  xxxii.  p.  128. 

14.  Stand-pipe  Accidents  and  Failures.     The  record  of  stand-pipe  failures  is 

brought  up  to  April,   1895,  in   an  important  series  of   articles  by 

W.  D.  Pence  in  Eng.  News,  1894,  xxxi.  and  1895,  xxxm.  p.  267. 

These  are  also  published  in  book  form.     Since  that  date  the  most 

important  articles  are  as  follows : 
Stand-pipe  Failures  at  Elgin,  111.     Caused  by  ice.     Eng.  News,  1900, 

XLIII.  p.  282. 

Stand-pipe  Failure  at  Collingswood,  N.  J.    Eng.  Record,  1900,  XLI.  p.  58. 
Stand-pipe  Failure  at  Garden  City,  Kan.     Eng.  News,  Oct.  i,  1896, 

xxxvi.  p.  218. 

15.  The   Compton   Hill    Masonry-enclosed   Stand-pipe  at    St.  Louis.     Eng. 

News,  1898,  xxxix.  p.  206;  Eng.  Record,  1899,  XL.  p.  220. 

1 6.  The   West    Arlington   Stand-pipe,  Baltimore.     Masonry-enclosed.     Eng. 

Record,  1899,  XL.  p.  413. 

17.  New    Water-tower    at    Schenectady,    N.   Y.     Masonry-enclosed.     Eng. 

Record,  1899,  xxxix.  p.  402. 

1 8.  Doten.      Concrete-steel    Water-tower   and    Stand-pipe   at   Fort   Revere, 

Hull,  Mass.   Jour.  New  Eng.  W.  W.  Assn.,  March,  1905.   Eng.  Record, 
1903,  XLVIII.  p.  218. 

19.  An  8o-ft.  Stand-pipe  of    Reinforced    Concrete  at  Milford,  Ohio.     Eng. 

News,  1904,  LI.  p.  184. 

20.  A  Large  Water  Tank  with  Vertical  Bracing  and  Top  Stiffening  Ring. 

Eng.  News,  1906,  LVI.  p.  499. 

21.  Reinforced  Concrete  Stand-pipes  at  Fort  Revere,  Mass.,    Milford,  Ohio, 

and  Attleboro,  Mass.     Munic.  Jour,  and  Engr.,  Dec.  5,  1906. 

22.  A   Large   Reinforced    Concrete    Stand-pipe   at   Attleboro,    Mass.    Eng. 

Record,  1906,  LIV.  p.  344  5  Eng.  News,  1907,  LVII.  p.  212. 


LITER  A  TURK.  741 

TANKS    AND    TOWERS. 

1.  Intze.     Description  of  Several  Towers  built  on  the  Intze  System.     Zeit. 

Ver.  deutsch.  Ing.,  1886,  xxx.  p.  26. 

2.  The  Norton  Tower  of  the  Liverpool  Water-works.     The  Engineer,  1892, 

LXXIV.  supplement  for  July  15;  Eng.  Record,   1891,  xxiv.  p.  278; 
Proc.  Inst.  C.  E.,  cxxvi.  p.  24. 

3.  The  Water-tower  at  Worms,  Germany.     Eng.  News,  1892,  xxvn.  p.  162  ; 

Eng.  Record,  1892,  xxv.  p.  141. 

4.  The   Water-tower    at    Mannheim,   Germany.     Eng.  Record,  1892,   xxvi. 

p.  219. 

5.  The    Elevated   Tank   at    Fairhaven,    Mass.     Eng.  Record,    1894,    xxix. 

p.  204. 

6.  Flad.     The  Laredo  Water-tower.     Eng.  News,  1894,  xxxr.  p.  206. 

7.  The  Scotland,  Pa.,  Wooden  Tank  and  Tower.     Eng.  Record,  1895,  xxxn. 

P-  457- 

8.  Steel  Water-tower  at  Paris,  111.     Eng.  Record,  1897,  xxxv.  p.  273. 

9.  Tank  of  Monier  Construction   at  Colbe,  Germany.     Zeit.    Ver.  deutsch. 

Ing.,  1897,  p.  301  ;  Eng.  News,  1899,  XLI.  p.  87. 
10.    Pressure  Storage-tanks  at  Babylon  and  Southampton,  N.  Y.     Eng.  News, 

1897,  xxxvm.  p.  429. 
n.    Fall  of   a  Water-tower  at  Marshall,  Minn.     Eng.  News,  1898,  xxxix. 

p.  70. 

12.  Marston.     The   Elevated   Water-tank   of    the    Iowa   State   Agricultural 

College.     Eng.  News,  1898,  xxxix.  p.  371. 

13.  Snow.     Steel  vs.  Wood  Tanks  (for  railroad  purposes).     Jour.  West.  Soc. 

Engrs.,  1899,  iv.  p.  268. 

14.  Ellis.     The  Elevated  Water-tank  at  Jacksonville,  Fla.     Eng.  News,  1899, 

XLI.  p.  258. 

15.  Storage-tanks  at  Lacona,  N.  Y.     Eng.  Record,  1900,  XLI.  p.  494. 
i6i    Water-tower  at  Murphysboro,  111.     Eng.  Record,  1900,  XLII.  p.  6. 

17.  Coggshall.      Fall  of  the  Fairhaven  Water-tower.     Jour.  N.  Eng.  W.  W. 

Assn.,  December,  1901.     See  also  Eng.  News,  1901,  XLVI.  p.  392. 

1 8.  The    Babylon   Water  Supply  Plant.     Description  of   a  compressed-air 

storage  system.     Eng.  Record,  1901,  XLIII.  p.  28. 

19.  Bowman.     Water-tank  and    Tower   for    East   Providence,  R.  I.     Jour. 

N.  Eng.  W.  W.  Assn.,  March,   1905.     See  also  Eng.  Record,  1904, 
L.  p.  580. 

20.  Elevated  Reinforced-concrete  Water-tanks  in  Cuba.     Eng.  News,  1908, 

Lix.  p.  471. 


CHAPTER    XXVIII. 
THE   DISTRIBUTING    SYSTEM. 

738.  General  Requirements. — A  distributing-  system  should  be  so 
designed  that  it  will  be  able  to  supply  adequate  quantities  of  water  to 
all  consumers,  and  that  this  will  be  accomplished  with  economy  and 
with  reasonable  security  against  interruption.  With  respect  to  the 
design  of  this  part  of  a  water- works  system,  the  uses  of  water  naturally 
fall  into  two  very  distinct  classes:  (i)  the  ordinary,  every-day  use  for 
domestic,  commercial,  and  public  purposes;  and  (2)  the  use  for  fire 
extinguishment.  In  the  former  case  the  consumption  is  relatively 
uniform  over  different  portions  of  the  city,  and  is  also  well  distributed 
over  many  hours  of  the  day;  in  the  latter  case  the  rate  is  likely  to  be 
extremely  high  for  a  very  short  period  of  time,  but  this  excessive  use 
of  water  will  usually  be  confined  to  a  comparatively  small  area.  To 
supply  water  in  the  former  case  requires  the  wide  distribution  of 
moderate  quantities,  while  in  the  latter  case  the  problem  is  rather  the 
concentration  of  large  volumes  within  a  narrow  district,  which  district 
may  be  situated  at  any  point  in  the  system. 

The  cost  of  distributing-mains  is  usually  the  largest  item  in  the 
cost  of  a  water-works,  and  consequently  much  care  must  be  taken  in 
the  design  of  this  part  of  the  system.  In  small  towns  it  will  often  be 
impracticable  to  provide  as  large  mains  as  would  be  required  to  furnish 
entirely  satisfactory  fire  protection,  and  in  such  a  case  the  advantages 
of  improved  fire  protection  must  be  carefully  balanced  against  increased 
cost  of  large  pipes. 

To  supply  water  to  all  consumers  requires  that  a  pipe  be  laid  in 
each  street,  except  in  those  cases  where  the  cross-streets  are  not  built 
upon.  In  the  outlying  districts,  pipes  are  laid  in  those  streets  where 
the  density  of  the  population  warrants  it,  according  to  the  judgment  of 
the  management,  but  much  difference  in  policy  exists  in  respect  to  the 
matter  of  extensions. 

The  distributing  system  includes,  besides  the  pipes,,  the  fire- 

742 


PRESSURE   REQUIRED.  743 

hydrants,  service  connections,  valves,  fountains,  watering-troughs, 
meters,  and  occasionally  other  details. 

739.  The  Pressure  Required. — a.  Ordinary  Service. — For  ordinary 
service  the  pressure  at  any  point  should  be  sufficient  to  supply  water 
at  a  reasonable  rate  in  the  upper  stories  of  houses  and  factories,  and 
in  business  blocks  of  ordinary  height.  This  will  require  at  the  street- 
level  a  pressure  of  from  25  to  35  pounds  in  residence  districts,  and 
usually  from  30  to  45  pounds  in  business  districts,  according  to  the 
character  of  the  buildings. 

b.  Fire  Service. — For  fire  purposes  the  pressure  required  in  the 
mains  depends  upon  whether  it  is  intended  that  fire-streams  shall  be 
furnished  directly  from  the  hydrants  or  whether  steam  fire-engines  are 
to  be  used.  In  small  cities  and  towns  it  is  of  the  greatest  advantage 
to  supply  fire-streams  without  the  use  of  engines,  and  in  most  such 
places  this  method  is  adopted,  fire-engines  being  sometimes  kept  in 
reserve,  however,  for  extraordinary  conflagrations.  In  pumping 
systems  the  most  common  arrangement  is  to  maintain  only  a  moderate 
pressure  for  ordinary  service,  and  at  times  of  fires  to  shut  off  the  reser- 
voir or  stand-pipe  if  there  be  one,  and  to  furnish  the  necessary  fire- 
pressure  direct  from  the  pumps.  In  many  plants,  however,  a  good 
fire-pressure  is  maintained  at  all  times,  and  this  may  be  done  without 
great  expense  if  those  buildings  which  demand  the  heaviest  pressures 
are  situated  on  the  lower  ground,  and  only  scattered  residences  on  the 
higher  ground.  Considerable  economy  is,  however,  usually  secured 
by  pumping  against  a  low  pressure  except  at  times  of  fires. 

In  large  cities  hydrant  fire-pressure  is  not  so  common,  but  if  the 
supply  is  by  gravity,  and  has  plenty  of  head,  a  hydrant  fire-pressure 
can  profitably  be  furnished,  at  least  for  all  except  the  densest  portion 
of  the  city  or  for  very  large  fires.  If  the  water  requires  to  be  pumped, 
then  only  the  ordinary  working-pressure  of  30  to  45  pounds  is  usually 
provided,  and  dependence  is  placed  on  fire-engines  to  supply  the 
deficiency.  To  furnish  fire-pressure  direct  from  the  pumps  at  all  times 
would,  in  the  case  of  large  cities,  be  very  costly,  and  to  increase  the 
pressure  at  times  of  fires  would  be  impracticable. 

If  hydrant  fire-pressure  is  to  be  supplied,  it  may  be  said  that  in 
general  the  pressures  in  the  mains  should  be  such  and  the  hydrants  so 
spaced  that  a  large  proportion  of  the  fire-streams  required  in  a  business 
district  should  be  of  240  to  250  gallons  capacity,  and  in  a  residence 
district  of  175  to  200. gallons  capacity.  If  low  hydrant  pressures  are 
furnished,  the  hydrants  must  be  spaced  closely,  and  if  high  pressures, 
then  a  wider  spacing  may  be  used.  It  will,  however,  be  found  that  a 


744  THE  DISTRIBUTING   SYSTEM. 

hydrant  pressure  lower  than  60  pounds  for  residence  districts  and  70 
pounds  for  business  districts  will  be  undesirable,  and  that  even  these 
values  will  call  for  a  close  hydrant-spacing.  Such  pressures  are, 
however,  quite  common.  Much  more  preferable  is  a  pressure  of  80  to 
100  pounds,  as  this  gives  good  streams  with  a  reasonable  hydrant- 
spacing.  The  lower  limits  of  60  to  70  pounds  may  then  be  accepted 
where  a  higher  pressure  cannot  be  furnished  without  a  large  extra 
expense,  as  in  the  case  of  many  gravity  systems;  but  where  the 
pressure  is  furnished  by  pumps,  and  especially  where  high  pressure  is 
furnished  only  during  fires,  the  expense  of  additional  head  is  not  great 
and  the  higher  values  of  80  to  100  pounds  should  be  adopted.  If 
steam  fire-engines  are  used,  then  it  is  only  necessary  to  supply  water 
to  the  hydrants  without  risk  of  causing  the  fire-pumps  to  operate  under 
suction.  This  low  pressure  may  result  in  interrupting  the  supply  for 
other  purposes  at  times  of  large  fires,  but  this  would  not  be  a  serious 
matter. 

The  pressures  here  considered  are  the  hydrant  pressures  at  times  of 
maximum  consumption,  and  refer  to  any  point  in  the  distributing 
system.  If  such  pressures  are  maintained  at  the  most  remote  points 
and  at  the  higher  elevations,  the  pressures  on  the  lower  ground  and  at 
points  nearer  the  pumps  or  reservoir  will  of  course  be  considerably 
higher.  There  will  in  general  be  certain  critical  points  which  will 
determine  the  pressures  to  be  maintained  at  the  source,  and  it  will  be 
a  matter  of  economy  to  assume  as  low  pressures  as  practicable  for  such 
points.  y . 

The  maximum  pressures  allowable  in  a  pipe  system  is  a  question 
of  expediency,  in  which  increased  cost  of  heavy  piping  and  increased 
danger  of  breakage  must  be  offset  against  any  advantage  derived  from 
high  pressures.  With  a  pumping  system  this  question  would  hardly 
arise,  but  with  a  gravity  system  supplied  from  an  elevated  source,  the 
head  available  may  be  greater  than  is  desired,  either  for  the  whole  or 
a  part  of  the  area  served,  in  which  case  some  method  of  reducing  the 
pressure  for  certain  districts  may  be  used  (Art.  648).  As  will  be  seen 
from  Table  No.  96,  the  maximum  fire-pressures  in  common  use  range 
from  about  IOO  to  160  pounds,  this  referring  to  the  pressures  at  the 
pumping-stations.  Generally  speaking,  pressures  exceeding  about 
130  pounds  are  found  to  give  much  extra  trouble  in  breakages,  and 
this  may  be  taken  as  about  the  limit  which  it  will  not  often  be  desirable 
to  exceed  for  any  considerable  part  of  the  distributing  system.  If  the 
elevations  of  different  portions  of  the  town  vary  widely,  then  two  or 
more  zones  of  pressure  may  be  used  (Art.  751). 


PRESSURE  REQUIRED. 


745 


In  Table  No.  96  are  given  the  ordinary  and  fire  pressures  in  the 
water- works  of  the  United  States,  as  stated  in  the  Manual  of  American 
Water-works,  1888,  and  which  serve  to  illustrate  the  practice  in  this 
respect.  The  pressures  given  refer  usually  to  the  pressures  at  the 
pumping-station.  There  has  been  a  marked  tendency  during  recent 
years  towards  higher  pressures.  (See  Art.  757.) 

TABLE  NO.  96. 

AVERAGE    WORKING-   AND    FIRE-PRESSURES    IN    1327    WATER-WORKS    OF    THE 

UNITED    STATES. 
The  table  gives  the  number  of  works  having  the  pressures  indicated  in  the  first  column. 


Pressure  per 
Square  Inch, 
Pounds. 

Average 
Working- 
pressure. 

Fire- 
pressure. 

Excess  of  Fire- 
over  Working- 
pressure. 

Under  20 

16 

CQ 

20-29 

60 

0V 

1:7 

•30—  30 

122 

o  / 
67 

J       O  ? 

40-49 

27O 

9 

w 
106 

50-59 

!59 

II 

8l 

60-69 

204 

27 

93 

70-79 

158 

36 

68 

80-89 

126 

73 

39 

90-99 

75 

70 

21 

100-109 

47 

143 

21 

IlO-lig 

28 

32 

8 

120-129 

27 

99 

ii 

130-139 

5 

30 

5 

140-149 

5 

23 

2 

150-159 

14 

54 

2 

160-169 

4 

13 

2 

170-179 

7 

ii 

180-189 

190—100 

yv    *  vv 
2OO 

j  j 

TABLE  NO.  97. 

ESTIMATED    NUMBER    OF   FIRE-STREAMS    REQUIRED    SIMULTANEOUSLY    IN    AMERICAN 
CITIES    OF    VARIOUS    MAGNITUDES. 


Population 
of 
Community. 

Number  of  Fire-streams  Required  Simultaneously. 

Freeman. 

Fanning. 

Shedd. 

Kuichling. 

t.OOO.  .  .  . 

2  to     3 

6 
6 

9 
12 

18 

20 
22 
28 

34 

38 

40 

44 
48 

7 

5,000  

10,000  

20,000.  .  .  . 
40,000.  .  .  . 
50  ooo     . 

4  to     8 
6  to  12 
8  to  15 
12  to  18 

5 
7 

10 

X4 

10 

14 

60,000.  .  .  . 
100,000.  .  .  . 
150  ooo 

15  to  22 
20  tO  30 

17 

22 

18 
25  . 

i  80  ooo     . 

30 

200,000.  .  .  . 

30  to  50 

•JQO  OOO 

746  THE   DISTRIBUTING   SYSTEM. 

740.  Number  and  Size  of  Fire-streams. — The  number  of  fire-streams 
which  should  be  simultaneously  available  in  any  given  town  will 
obviously  vary  greatly  with  the  character  of  the  buildings,  width  of 
streets,  etc.  This  subject,  together  with  other  questions  relating  to 
fire-protection,  has  been  thoroughly  discussed  in  valuable  papers  by 
Mr.  Freeman*  and  Mr.  Fanning, t  to  which  reference  should  be. made 
for  more  detailed  information.  The  general  conclusions  of  these 
engineers  as  to  the  number  of  streams  required,  and  similar  estimates 
by  Mr.  Shedd  and  by  Mr.  Kuichling,  are  given  in  Table  No.  974 
The  values  given  by  Mr.  Kuichling  may  be  expressed  by  the  formula 

y  =  2.8  4/J, 

where  y  =  number  of  streams,  and  x  =  population  in  thousands. 

The  figures  given  in  the  table  relate  to  cities  of  average  character, 
and  are  the  total  number  of  streams  required  simultaneously  for  the 
entire  city.  In  regard  to  the  actual  number  required  at  any  one  point 
Mr.  Freeman  estimates  that  as  a  general  statement  two-thirds  of  his 
estimated  number  should  be  capable  of  being  ' '  concentrated  upon  any 
one  square  in  the  compact  valuable  part  of  the  city  or  upon  any  one 
extremely  large  building  of  special  hazard."  For  compact  residence 
districts  one-fourth  to  one-half  the  number  given  in  the  table  would 
usually  be  sufficient,  and  for  small  detached  dwellings  two  to  three 
good  streams  would  answer.  All  these  estimates  should,  however,  be 
used  with  much  caution,  and  should  be  varied  to  suit  local  conditions. 
Different  large  cities  are  likely  to  be  of  about  the  same  general  char- 
acter and  the  requirements  will  be  similar,  but  in  small  cities  and  towns 
the  requirements  for  fire-protection  may  differ  widely.  For  example, 
in  a  country  town  of  4000  to  5000  inhabitants  in  which  only  a  small 
mercantile  business  is  carried  on,  the  fire  risk  is  not  great,  while  in  a 
town  of  the  same  size  whose  prosperity  depends  entirely  upon  two  or 
three  large  factories,  located,  perhaps,  in  one  large  group  of  buildings, 
a  fire  would  be  a  very  serious  matter.  In  the  former  case  four  or  five 
fire-streams  would  .be  sufficient,  while  in  the  latter  case  eight  or  ten 
should  be  supplied. 

The  number  of  fire-streams  given  in  the  table  is  based  upon  a  size 
of  stream  of  about  250  gallons  per  minute,  which  is  generally  consid- 
ered tq  be  about  right  as  an  average  value  for  good  fire-streams  in 

*  Jour.  New  Eng.   W.   W.  Assn.,  1892,  vii.  p.  49. 

f  Proc.  Am.  W.  W.  Assn.,  1892,  p.  88;  Eng.  News,  1892,  July,  p.  42. 

|  From  a  paper  by  E.  Kuichling  in  Trans.  Am.  Soc.  C.  E.,  1897,  xxxvm.  p.' 15. 


LOCATION  OF  HYDRANTS.  747 

business  districts.  For  a  residence  district  175-  to  2OO-gallon  streams 
will  usually  meet  the  requirement. 

741.  Location  of  Hydrants. — Fire-hydrants  must  be  sufficiently 
numerous  and  so  located  as  to  meet  the  requirements  regarding 
number  and  size  of  fire-streams  set  forth  in  the  preceding  article. 
Hydrants  are  one-way,  two-way,  three-way,  etc.,  according  to  the 
number  of  hose-connections  provided.  For  most  purposes  the  two- 
way  hydrant  is  considered  the  most  convenient,  but  in  the  dense 
portion  of  a  large  city,  where  many  connections  must  be  provided, 
three-way  and  four-way  hydrants  can  be  used  to  good  advantage. 
Hydrants  should,  in  any  case,  be  numerous  enough  to  enable  the 
required  number  of  streams  to  be  furnished  with  a  suitable  nozzle- 
pressure.  At  points  where  a  large  number  of  streams  are  required, 
•^re-cisterns  are  sometimes  used  instead  of  hydrants.  These  cisterns 
are  fed  by  large  pipes,  and  have  an  advantage  over  hydrants  in  that 
they  allow  several  steamers  to  obtain  their  supply  at  one  point. 

For  a  25O-gallon  stream  the  required  nozzle-pressure  is  45  pounds, 
and  the  loss  of  head  per  100  feet  of  ordinary  2j-inch  hose  is  about  18 
pounds  (see  Table  No.  50,  page  250),  so  that  with  a  hydrant  pressure 
of  100  pounds  the  length  of  hose  to  supply  a  25O-gallon  stream  cannot 
exceed  300  feet.  A  175-gallon  stream,  with  a  i-inch  nozzle,  requires 
35  pounds  nozzle-pressure,  and  causes  a  loss  of  head  of  9  pounds  per 
100  feet  of  hose.  With  a  hydrant  pressure  of  100  pounds  the  length 
of  hose  in  this  case  might  be  700  feet.  With  a  hydrant  pressure  of  75 
pounds,  which  is  quite  common,  a  25O-gallon  stream  could  not  be 
supplied  through  a  length  of  hose  greater  than  about  200  feet,  and  a 
1 75 -gallon  stream  through  a  length  greater  than  about  450  feet. 
Hence  the  general  rule  that  hydrants  should  be  so  spaced  that  no  line 
of  hose  should  exceed  500  to  600  feet,  and  for  at  least  half  of  the 
streams  required  at  any  point  the  length  of  hose  should  not  exceed 
250  to  350  feet,  according  to  the  hydrant  pressure.  These  lengths 
cannot  be  much  increased  even  where  fire-engines  are  used.  In  out- 
lying districts  two  two-way  hydrants  should  be  available  at  any  point, 
with  a  distance  of  not  more  than  500  to  600  feet  to  the  more  remote 
of  the  two. 

The  most  convenient  location  for  hydrants  is  at  the  street  intersec- 
tions, as  they  are  then  readily  accessible  from  four  directions.  In 
cities  of  moderate  size  the  required  number  of  streams  can  readily  be 
supplied  by  locating  a  hydrant  at  each  street  intersection,  but  in  large 
cities  intermediate  hydrants  are  often  necessary.  Thus  if  the  blocks 
in  Fig.  220  are  300  feet  long  in  each  direction,  and  a  two-way  hydrant 


748 


THE  DISTRIBUTING   SYSTEM. 


is  placed  at  each  corner,  then  a  fire  at  A  could  be  served  from  eight 
hydrants,  with  a  maximum  length  of  hose  of  450  feet,  giving  sixteen 


t/ 


FIG.  220. 


FIG.  221. 


good  fire-streams ;  while  a  fire  at  a  street-corner  could  be  served  from 
thirteen  hydrants,  eight  of  which  would,  however,  require  hose-lengths 
of  600  feet.  With  blocks  600  feet  by  300  feet,  as  in  Fig.  221,  a  two- 
way  hydrant  at  each  intersection  would  supply  not  less  than  eight 
streams  at  any  point,  without  exceeding  600  feet  of  hose.  If  only  four 
streams  are  required,  then  one-fourth  of  the  hydrants  might  be  omitted, 
or  every  other  hydrant  in  alternate  streets,  as  hydrants  i,  2,  and  3. 
This  would  just  be  within  the  requirement  of  a  maximum  hose-length 
of  600  feet.  To  omit  half  the  hydrants,  or  to  place  them  at  one-half 
the  intersections,  would  require  the  use  of  750  feet  of  hose  at  certain 
points  to  supply  two  out  of  the  four  fire-streams.  Such  a  spacing 
would  therefore  be  inadequate.  The  necessary  hydrant-spacing  to 
furnish  any  given  number  of  streams  can  be  determined  by  the  method 
here  illustrated. 

742.  General  Arrangement  of  the  Pipe  System. — From  the  data  of 
Chapter  II  (page  32)  it  is  evident  that  the  fire  demand  will  largely 
govern  in  the  design  of  the  pipe  system.  This  is  more  and  more  true 
the  smaller  the  town  or  district  considered,  and  for  single  blocks  the 
ordinary  consumption  can  practically  be  neglected.  To  supply  long, 
narrow  districts,  the  general  scheme  would  be  to  furnish  the  water 
mainly  through  a  single  large  pipe  of  gradually  decreasing  size,  with 
small  parallel  and  branch  mains  supplying  the  side  streets,  somewhat 
as  in  Fig.  228  (page  766),  districts  I  and  3.  For  broad  areas,  such 
as  comprise  the  larger  portions  of  most  cities,  the  general  arrangement 
usually  adopted  is  to  provide  large  mains  at  intervals  of  J  to  £  mile, 
and  to  fill  in  between  these  mains  with  smaller  pipes,  thus  forming  a 
gridiron  system.  The  smaller  pipes  are  designed  with  special  refer- 
ence to  supplying  the  fire-streams  which  are  required  at  any  point, 
without  too  great  a  loss  of  head,  while  the  larger  mains  must  be 
designed  with  reference  to  the  ordinary  consumption  as  well  as  to  the 


GENERAL   ARRANGEMENT  OF   THE  PIPE  SYSTEM.  749 

fire  demand.      The  gridiron   system  is   well   illustrated   by   Fig.    222, 
which  shows  a  section  of  the  St.  Louis  distributing  system. 

A  general  principle  which  should  be  kept  in  mind  when  laying  out 
a  system  is  to  so  arrange  the  large  mains  that  the  smaller  cross-mains 
may  be  fed  from  both  ends,  since  a  pipe  so  fed  is  equivalent  to  two 
pipes.  It  can  furnish  double  the  number  of  streams  with  the  same  loss 
of  head,  or  the  same  number  of  streams  with  about  one-fourth  the  loss 
of  head,  as  when  fed  from  one  end  only.  This  principle  also  makes  it 
desirable  to  lay  connecting  pipes  between  separated  districts,  even 
when  such  pipes  are  not  required  for  supplying  local  consumers.  In 
the  case  of  fire,  each  district  may  then  be  served  from  both  ends. 
This  plan  is  well  illustrated  in  Fig.  228.  In  a  gridiron  system  it  is, 
for  the  same  reason,  desirable  to  provide  large  mains  near  the  outside 
edges  of  the  network.  Extensions  will  of  course  make  it  impossible 
to  do  this  at  all  times,  but  the  desirability  of  having  a  circulating 
system,  and  avoiding  dead  ends  as  much  as  possible,  should  be  kept 
well  in  mind.  Dead  ends  are  also  objectionable  on  account  of  the 
stagnation  which  exists  in  the  pipes  and  the  deterioration  of  the  water 
which  is  likely  to  ensue. 

The  size  of  mains  and  cross  lines  in  the  gridiron  system  will  depend 
largely  upon  the  number  of  fire-streams  required  at  any  point.  In 
small  cities,  and  outlying  districts  of  large  cities,  6-inch  cross-mains 
with  8-,  10-,  or  1 2-inch  pipes  at  intervals  of  four  to  six  blocks  is  a 
common  arrangement.  Four-inch  pipe  should  rarely  be  used  to  supply 
hydrants.  For  compactly  built  districts  many  of  the  cross-pipes 
require  to  be  8  inches,  and  a  more  frequent  use  made  of  12-  and 
1 6-inch  pipes.  A  good  arrangement  for  a  comparatively  large  demand 
is  to  lay  6-inch  pipes  lengthwise  of  the  blocks  and  8-inch  pipes  cross- 
wise. To  supply  large  areas,  still  larger  feeders,  such  as  24-,  36-, 
and  48-inch  pipes,  will  be  required.  These  are  added  to  the  system 
from  time  to  time,  as  the  needs  of  the  city  require  and  as  the  pressures 
become  low  through  increased  consumption.  They  should  be  so 
located  and  connected  with  the  larger  distributing-mains  as  to  reinforce 
the  pressure  where  most  deficient. 

743.  Maximum  Rates  of  Supply  for  Different  Areas. — For  the  pur- 
pose of  calculating  the  distributing  system  it  is  necessary  to  know  the 
maximum  rate  of  consumption  for  the  entire  city,  and  for  large  and 
small  sections  of  the  same,  with  suitable  consideration  for  future 
growth.  The  rate  for  the  entire  city  will  enable  the  main  supply- 
conduit,  or  the  principal  force-main,  to  be  determined.  For  calculat- 
ing the  main  distributing-pipes  the  city  should  be  divided  into 


750 


THE  DISTRIBUTING    SYSTEM. 


5o  inch  pipe  shown  thus  .... 


FIQ.  222. — SECTION  OF  ST.  Louis  DISTRIBUTING  SYSTEM. 


MAXIMUM  RATE   OF  SUPPLY  FOR   DIFFERENT  AREAS.       751 

relatively  large  districts,  corresponding-  to  the  most  probable  location 
of  such  main  arteries ;  then  for  the  smaller  pipes  the  demand  for  still 
smaller  sections  must  be  considered,  and  so  on. 

The  extent  to  which  provision  for  future  growth  should  be  made 
will  be  different  in  the  various  parts  of  the  system,  and  will  vary 
according  to  circumstances.  It  will  not  usually  be  necessary  to  design 
for  more  than  fifteen  to  twenty  years  in  the  future,  and  sometimes  even 
for  less.  In  making  extensions,  large  mains  can  readily  be  added  from 
time  to  time,  and  these  can  often  be  placed  where  no  pipes  now  exist 
A  better  pressure  will  eventually  be  furnished  by  several  good-sized 
mains,  placed  some  distance  apart,  than  by  one  very  large  main. 
For  small  cities,  where  the  fire  demand  is  relatively  large  and  does 
not  increase  rapidly  with  the  population,  a  small  increase  in  size  of 
mains  will  make  the  system  serviceable  for  a  relatively  long  period  in 
the  future,  and  in  this  case  twenty-five  or  thirty  years'  growth  might 
well  be  provided  for.  For  that  part  of  a  system  serving  only  a  limited 
territory  provision  should  be  made  for  a  fully  built-up  condition. 

The  maximum  rate  of  consumption  for  the  entire  city  has  already 
been  discussed  in  Chapter  II,  page  32.  From  the  data  there  given 
the  ordinary  maximum  rate  is  seen  to  be  from  200  to  250  per  cent  of 
the  yearly  average.  If  the  yearly  average  be  100  gallons  per  capita 
daily,  the  maximum  ordinary  rate  will  then  be  about  250  gallons  per 
capita  per  day,  or  0.17  gallon  per  capita  per  minute.  The  maximum 
fire  rate  by  Kuichling's  formula  of  Art.  740,  assuming  25O-gallon 
streams,  is  250  X  2.8  Vx,  =  700  Vx  gallons  per  minute,  where  x  = 
population  in  thousands.  Thus  for  a  population  of  1000  the  ordinary 
maximum  rate  may  be  about  170  gallons  per  minute,  while  the  fire 
rate  is  likely  to  be  700  gallons,  or  four  times  as  much. 

After  estimating  the  maximum  rate  of  consumption  for  the  city  as 
a  whole,  the  same  should  be  done  for  the  several  districts,  the  probable 
future  population,  the  maximum  ordinary  rate,  and  the  maximum  fire 
demand  being  estimated  for  each  district  independently.  The  required 
number  of  fire-streams  for  the  separate  districts  should  be  determined 
in  accordance  with  the  data  previously  given.  In  combining  the  con- 
sumption for  two  or  more  districts,  the  required  fire  supply  should  be 
found  by  considering  the  district  as  a  whole  and  not  by  adding  the 
separate  requirements.  The  fire  demand  will  increase  but  little  as  the 
size  of  district  increases. 

To  illustrate  the  points  here  considered,  and  other  questions  per- 
taining to  the  design  of  a  distributing  system,  an  arrangement  of  pipes 
will  be  assumed  as  shown  in  Fig.  228,  page  766.  This  would  be  a 


752  THE  DISTRIBUTING  SYSTEM. 

suitable  arrangement  for  the  city  of  Madison,  Wis.,  under  certain 
assumed  conditions  which,  for  purposes  of  illustration,  are  different  in 
some  respects  from  the  actual  conditions.  Pipes  are  shown  where 
most  needed,  although  there  are  a  few  more  pipes  actually  laid  than 
are  shown.  With  respect  to  the  natural  conditions  and  the  probable 
location  of  main  arteries,  the  city  may  be  divided  into  about  ten 
districts  as  indicated.  District  No.  2  includes  important  factories. 
District  No.  9  is  a  small  suburb.  The  probable  population  fifteen  to 
twenty  years  hence,  immediately  adjacent  to  the  lines  or  which  will  be 
served  by  them,  is  assumed  to  be  as  given  on  the  diagram  ;  also  the 
number  of  fire-streams  simultaneously  required  in  each  district.  The 
number  for  the  entire  city  is  taken  at  fifteen  25o-gallon  streams.  The 
maximum  rate  of  ordinary  consumption  is  assumed  to  be  125  gallons 
per  capita  per  day,  the  average  rate  at  the  present  time  being  about 
45  gallons.  The  maximum  rate  of  supply  required  for  each  district 
for  ordinary  and  fire  supply  will  then  be  about  as  given  in  Table 
No.  101,  page  767.  For  districts  Nos.  2  and  3  together  the  maximum 
rate  would  be  380  gallons  per  minute  for  ordinary  consumption  plus 
2000  gallons  for  fire  purposes,  =  2380  gallons  per  minute.  Similarly, 
districts  Nos.  4  to  10  would  require  altogether  21 10  gallons  for  ordinary 
purposes,  plus  15  fire-streams,  or  a  total  of  6560  gallons  per  minute. 
The  calculation  of  the  pipe  system  is  further  considered  in  Art.  750. 

A  larger  provision  for  the  future  than  here  made  would  probably 
be  desirable  for  the  main  pipes  in  the  vicinity  of  the  pumping-station 
and  in  the  denser  portion  of  the  city,  as  no  additional  lines  of  pipes 
would  ever  be  needed  here  to  supply  the  local  demand.  At  outlying 
districts  many  streets  remain  unoccupied,  which  gives  opportunity  for 
enlarging  the  capacity  when  pipes  are  laid  in  these  streets. 

744.  Velocities  of  Flow  for  Fire  Supplies.  —  In  calculating  a  pipe 
system  it  is  convenient  to  get  first  a  good  notion  of  the  practicable  and 
economical  velocities  which  may  ordinarily  be  used  for  the  maximum 
fire  draught.  The  most  suitable  velocities,  or  losses  of  head,  will 
depend  somewhat  upon  the  system  of  supply,  and  also  upon  the  loca- 
tion and  elevation  of  the  pipes  in  question.  The  various  conditions 
will  be  included  by  considering  the  problem  with  respect  to  the  follow- 
ing cases : 

(1)  A  pumping  system  in  which  fire  pressure  is  constantly  main- 
tained. 

(2)  A  pumping  system  in  which  fire  pressure  is  maintained  only  at 
times  of  fires,   the  pressure  at  other  times   being   sufficient   only  for 
ordinary  purposes. 


VELOCITIES   OF  FLOW  FOR  FIRE   SUPPLIES.  7  S3 

(3)  A  gravity  system  with  sufficient  pressure  for  fire  purposes. 

(4)  A  pumping  or  gravity  system  furnishing  a  low  working-pres- 
sure only,  fire-engines  being  used. 

(i)  In  this  case  if  it  be  assumed  that  a  certain  minimum  hydrant 
pressure  is  required  at  various  points,  this  pressure,  and  the  loss  of  head 
in  the  pipe  system,  will  control  the  head  against  which  the  pumps 
operate  ;  and  as  this  head  is  constantly  maintained,  the  disadvantage 
of  small  pipes  and  large  frictional  loss  is  very  great.  The  best  size  of 
pipes,  or  the  economical  velocities,  will  in  this  case  be  different  from 
those  given  in  Chapter  XXVI,  page  370,  but  may  be  determined  in  a 
similar  way. 

Let  Q  =  average  yearly  rate  of  flow,  or  the  average  rate  of  con- 
sumption for  any  given  district  served  by  a  given  pipe.  Let  Ql  = 
maximum  rate  of  fire  demand,  plus  the  rate  for  ordinary  purposes.  In 
the  case  under  consideration  the  pressure-head  at  the  pumps  will  be 
determined  by  <2P  but  the  actual  yearly  expense  of  pumping  will  be 
proportional  to  the  volume  Q,  since  the  total  amount  pumped  for  fires 
is  very  small.  We  then  have,  as  in  eq.  (5),  page  604, 


and,  as  in  eq.  (6),  the  yearly  cost  = 

A  =  bsQ  +  20r 

Substituting  the  value  of  s,  differentiating,  etc.,  as  on  page  605,  we 
find  that  the  economical  velocity 


The  economical  velocity  in  this  case  is  thus  equal  to  the  economical 
velocity  for  the  average  rate  of  consumption,  as  given  on  page  605, 

(0  Vs6 
multiplied  by  f  -4-  1     ,  or  approximately  by  the  cube  root  of  the  ratio  of 

the  maximum  to  the  ordinary  rate.  For  small  areas,  such  as  two  or 
three  blocks,  the  maximum  rate  is  likely  to  be  fifty  or  more  times  the 
ordinary  rate,  but  for  areas  consisting  of  several  blocks  the  ratio  is 
much  less.  Thus  in  the  table  on  page  767,  district  No.  5,  the  ratio 
of  the  maximum  to  the  average  rate  is  about  12,  and  in  No.  2  it  is 
about  23,  while  for  districts  Nos.  4  to  10  combined  it  is  only  4. 

To  illustrate  the  variation  in  economical  velocity  with  varying  con- 


754  THE   DISTRIBUTING   SYSTEM. 

ditions,  such  velocities  have  been  calculated  for  certain  cases,  taking 
the  upper  figures  of  Table  No.  77,  page  606,  as  a  basis.  The  results 
are  as  follows : 

Ratio  of  maximum  to  ordinary  rate 2  4  10  25  50 

6-inch  pipe. ..  2.3  3.0  4.2  5.8  7.4 

8-  "    •     "...  2.5  3.2  4.5  6.2  8.0 

Economical  velocities...^  10-   "         "...  2.7  3.4  4.7  6.6  8.5 

I  12-  "         "...  2.8  3.6  5.0  7.0 

U6-  "         "    ...  30  3.9  5-4 

For  still  larger  pipes  the  ratio  will  usually  be  quite  small,  and  the 
velocities  therefore  not  much  greater  than  given  in  Table  No.  77. 

(2)  Where  fire  pressure  is  furnished  only  when  needed,  and  a  com- 
paratively low  pressure  is  used  at   other   times,   the  pipes  are  to   be 
designed,  first,  to  give  economical  velocities  for  ordinary  service,  and, 
second,  to  give  practicable  velocities  and  losses  of  head  for  fire  service. 
It  is  desirable  to  limit  the  loss  of  head  so  that  the  fire  pressure  at  the 
pumps  will  not  need  to  be  excessively  high,  both  to  avoid  the  use  of 
extra  thick  pipe  and  heavy  plumbing,  and  to  avoid  too  large  variations 
in  the  pump  pressures.     Ordinarily  about  120  to  130  pounds  is  as  high 
a  pump  pressure  as  is  desirable  to  use,  but  sometimes  a  greater  pressure 
is  necessary  to  furnish  fire-streams  on  the  higher  areas   of  the   city. 
With  a  hydrant  pressure  of  80  to  100  pounds,  and  a  pump  pressure  of 
120  to  130  pounds  as  a  desirable  maximum,  the  allowable  velocities 
of  flow  will  not  much  exceed  those  given  in  ease  (i),  and  may  in  fact 
be  lower.      The  smaller  mains  would  seldom  be  affected  in  any  event, 
as  a  change   of  2   inches  in  the  diameter  of  a   small   main  so  greatly 
changes  its  capacity,  but  some  of  the  larger  mains  might  be  reduced 
somewhat  in  size. 

(3)  Where  a  gravity  system  furnishes  a  certain  definite  pressure  at 
the  distributing-reservoir,  the  loss  of  head  allowable  in  the  pipe  system 
is  more  or  less  closely  defined.      If  the  available  pressure  is  low,  the 
distributing-pipes  will   need  to  be  made  large  in  order  to   obtain   as 
much   head   at  the  hydrant  as  possible,  but  for  certain  areas  and  for 
large  fires  it  may  be  cheaper  to  employ  fire-engines  than  to  go  to  a 
large  expense  to  save  loss  of  head  in  conduit  and  distributing-pipes. 
Where  the  available  pressure  is  high,  then  the  loss  of  head  in  the  pipe 
system  may  equal  the  difference  between  this  and  a  hydrant  pressure 
of,  say,  100  pounds. 

Whenever  a  certain  definite  loss  of  head  is  allowable  between  a 
reservoir  and  a  certain  section  of  the  city,  the  proper  distribution  of 
this  loss  among  large  and  small  mains  is  a  matter  of  considerable  im- 
portance. A  general  solution  of  the  problem  will  be  of  some  aid. 


VELOCITIES   OF  FLOW  FOR  FIRE   SUPPLIES.  755 

In  Fig.  223,  let  a\ ,  Qlt  vlt  /x,  //t,  and  sl  be,  respectively,  the 
diameter,  discharge,  velocity,  length  of 
pipe,  loss  of  head,  aad  hydraulic  slope 
with  respect  to  a  main,  AB\  and 
let  d2,  <22,  etc.,  refer  to  corresponding 
quantities  in  a  branch  BC,  of  which 
there  are  several  of  the  same  length 
and  size.  Let  n  =  number  of  branches ; 
H  =  total  loss  of  head  from  A  to  C, 
=  k^  -|-  kr  The  total  cost  of  the 
system  is,  by  eq.  (i),  page  604, 


FIG.  223. 


A  = 


n/2) 


(2) 


Substituting  the  value  of  d  as  derived  from  eq.  (5),  page  604,  we  have 

/  1.325 


+  "Q^ 


(3) 


If  we  differentiate  with  respect  to  h^  ,  or  add  an  increment  dk,  ,  we  at 
the  same  time  subtract  the  same  amount  from  7/2  ,  since  h,  +  ^2  =  H  = 
a  constant.  Hence  dh,  =  —  dk2.  Differentiating  then,  and  equating 
to  zero,  etc.,  we  have  for  a  minimum  cost 


or  since,  in  general,  j  =  s,  we  have 


s  ••      n.74Q.4*> 


or,  practically, 


J'  (     Q*      Y 

7--\-^-     •   • 


(A\ 


In  the  case  where  nQ2  =  Ql  ,  or  where  all  the  branch  pipes  are  dis- 

s       /i  V4 

charging  equally,  then  —  =  (—  j    ;  that  is,  the  hydraulic  slopes  for  AB 

and  each  of  the  branches  BC  should  be  as  i  :  n  4.  Thus  if  a  single 
large  pipe  branches  into  ten  smaller  ones,  each  designed  to  carry  one- 
tenth  the  total  volume,  then  the  hydraulic  slopes  should  be  as 


756  THE  DISTRIBUTING   SYSTEM. 

I  :  io-4  =  I   :  2^.     If  four  of  the  smaller  pipes  be  designed  to  carry  the 
entire  volume,  as  for  fire  purposes,  then  Q2  =  J<2i  >  and  we  have 


_ 
'  3.6' 

The  actual  sizes  of  pipes  for  any  given  total  loss  of  head  and  discharge 
can  readily  be  found  by  trial  by  the  aid  of  the  diagram  on  page  243. 

The  general  principle  here  brought  out  is  that  in  a  distributing 
system  containing  a  large  number  of  small  pipes,  only  a  few  of  which 
are  ever  discharging  at  their  full  capacity  at  the  same  time,  most  of 
the  loss  of  head  at  times  of  fires  should  occur  in  the  near  vicinity  of 
the  fire,  and  relatively  little  in  the  large  mains  leading  thither. 

As  already  stated,  the  possible  variation  in  size  in  the  smaller  pipes 
will  be  very  little,  but  in  the  larger  and  more  expensive  mains  con- 
siderable economy  can  be  secured  by  a  careful  study  of  the  problem, 
and  by  calculations  of  two  or  more  possible  arrangements. 

(4)  Where  a  pressure  sufficient  only  for  ordinary  purposes  is  pro- 
vided, the  pipes  must  still  be  designed  largely  with  reference  to  fire 
consumption,  so  that  they  will  at  all  times  be  able  to  furnish  full  sup- 
plies to  the  fire-engines  without  suction.  The  problem  is  essentially 
the  same  as  that  discussed  under  (3). 

745.  Loss  of  Head  in  Distributing-pipes,  —  To  aid  in  the  selection  of 
the  smaller  sizes  of  pipes  it  will  be  convenient  to  tabulate  the  losses  of 
head  in  such  pipes,  when  supplying  various  numbers  of  fire-streams. 
Table  No.  98  is  made  up  in  this  way,  the  values  given  being  based  on 
the  diagram  of  page  243. 

It  will  be  readily  seen  that  for  any  given  number  of  streams  the 
choice  of  pipe  will  usually  be  confined  to  two  or  possibly  three  sizes, 
since  the  loss  of  head  varies  so  rapidly  with  change  of  size.  The 
ordinary  consumption  may  be  neglected  for  short  pipes  supplying  only 
one  or  two  blocks,  while  for  larger  areas  the  ordinary  rate  may  be 
converted  into  an  equivalent  number  of  fire-streams. 

For  example,  if  ten  streams  are  required,  the  choice  would  prob- 
ably be  either  a  12-,  14-,  or  i6-inch  pipe.  In  the  case  of  a  city  where 
1  2  -inch  pipes  are  used  for  comparatively  short  submains,  such  a  size 
might  be  employed,  but  where  serving  larger  districts,  or  where  the 
available  head  is  small,  a  1  2-inch  would  be  too  small,  and  a  14-  or 
1  6-inch  should  be  used.  The  1  6-inch  pipe  would  probably  be  the  best 
size  if  the  district  comprised  a  large  portion  of  a  small  city,  where  the 
large  main  would  be  relatively  long  and  the  ratio  of  fire  to  ordinary 
consumption  not  very  large.  In  the  same  way  a  supply  of  six  fire- 


LOSS   OF  HEAD    SAT  DISTRIBUTING-PIPES. 


7S7 


TABLE  NO.  98. 

VELOCITY  OF  FLOW  AND  LOSS  OF  HEAD  PER  IOOO  FEET  IN  DISTRIBUTING-PIPES  WHEN  DELIVERING  GIVEN  NUMBERS  OF 
250-GALLON  FIRE-STREAMS. 
Loss  of  head,  in  feet,  given  by  light-faced  type.  Loss  of  head,  in  pounds,  given  by  bold-faced  type. 

0 

c 

JO  SS01 

O 

-PA 

en 

o 

C 
I 

jo  ssoq 

r>-  « 

_      CO              M 

O   ^-    <tio    co  O 

O 

M                M               C4     M 

•An 

-00  [3  A 

N            pj            CO           4 

"o 

(S 

ToslJl 

m        t^        t* 

a>    co  co  in  o  oo 

O  <n   O  tx  \noo 

O                  M        '      cJ        * 

CO   M       Tt   M     VO     <* 

•An 

M              CO              <O 

in           rj-           O 

20-inch. 

jo  ssoq 

T*-<*   ooo    N  ^-  r-« 

O   O     to  M 

COM       ^H, 

t-CO    OTf 

-^A 

VO                M                M                M 

tr>          oo 

W           CO          ^t          vr> 

vO          r** 

i6-inch. 

jo  ssoq 

0^^«Ot^COCOOO»          VO 

M    '    (SM    eoMu^«    ocnco^ 

•An 

Tt-         N          O         oo          ^         O 

0»             CO            rj-            •*           O            00 

a 

0 

a 

jo  ssoq 

c.   0 

M«o«co«w*      ^   : 

N     M 

COM    mw    t^coO^r^t1^ 

•An. 

0 
M 

O         c^         N          co         T$- 

CO           ^           U^          O           OO               • 

1 
'I 

jo  ssoq 

CO  M      rt  M 

0  «    O  *   >^vo    «  o>     • 

. 

•An 

OO             ""> 

a        co 

*      *      * 

.c 
c 

"u 

c 

3 

u 

jo  ssoq 

»n  o»    rj-  «    O\  C-N 

10             0^             M         . 

TJ-M     t-co    0   -*•    JOVO     u-,0     t^iO       .            .            :            -            .            . 

•An 

jo  ssoq 
•An 

jo  ssoq 

co        4-        ""> 

rl-00    00  10          VO           0\ 
VOW      (NIOWO»WCO 

«           O         »n          O\ 
CO          •<*         0           ^ 

0            00             g                .                '. 

0 

i 

a 
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jo  ssoq 
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J  'IBS 

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tn  c«      •            •             '            •            

758  THE   DISTRIBUTING   SYSTEM. 

streams  would  in  most  cases  call  for  either  a  10-  or  12-inch  pipe,  and 
four  streams  an  8-  or  lO-inch,  etc.  It  is  to  be  particularly  noted  that 
a  4-inch  pipe  is  hardly  suited  for  even  a  single  stream,  and  a  6-inch 
pipe  for  not  more  than  two  streams. 

The  table  and  computations  refer  of  course  to  the  actual  flow  in  the 
pipe.  A  pipe  fed  from  both  ends  and  supplying  intermediate  hydrants 
is  equivalent  to  two  pipes  and  should  be  so  calculated.  The  diagram 
on  which  the  table  is  based  allows  about  20  per  cent  increase  in  loss  of 
head  for  corrosion,  but  in  many  cases  a  considerably  greater  allowance 
should  be  made  for  the  smaller  sizes,  and  unless  it  is  quite  certain  that 
corrosion  will  not  be  great,  4-inch  pipes  should  not  be  used  at  all  to 
supply  hydrants. 

As  it  is  frequently  desirable  to  ascertain  the  size  of  a  single  large 
pipe  equivalent  to  several  small  pipes,  the  relative  discharging 
capacities  of  pipes  of  different  sizes  for  the  same  loss  of  head  are  given 
in  Table  No.  99,  the  capacity  of  a  4-inch  pipe  being  taken  as  i. 

TABLE    NO.   99. 

RELATIVE    DISCHARGING    CAPACITIES    OF    PIPES    FOR    THE    SAME    LOSS    OF    HEAD. 

Size  of  pipe 468         10       12       14       16       20         24      30         36 

Relative  capacity I       3        6^      12       20       30       43       80        130     235       390 

746.  General  Problems  Pertaining  to  the  Flow  through  Compound 
Pipes. — In  calculating  the  flow  through  a  system  of  pipes,  several 
problems  will  arise.  Some  of  these  can  be  solved  only  by  rough 
approximations,  but  there  are  two  classes  of  problems  for  which  simple 
general  solutions  can  readily  be  found.  Where  a  distributing  system 
consists  of  but  a  few  pipes,  or  is  in  the  form  of  a  long  narrow  district, 
the  formulas  derived  can  often  be  easily  and  directly  applied.  Where, 
however,  the  pipes  spread  over  a  broad  area  it  is  impracticable  to 
obtain  anything  more  than  a  very  rough  approximation  to  exact 
results,  but  the  general  relations  brought  out  by  the  solution  of  these 
two  cases  will  assist  in  making  reasonable  assumptions  in  the  more 
complicated  case. 

The  two  general  cases  to  be  considered  are: 

(1)  The  discharge  from,   or  loss  of  head  in,  a  single  pipe-line  of 

varying  cross-section. 

(2)  The  discharge  from,  or  loss  of  head  in,  a  line  of  two  or  more 

pipes  extending  between  any  two  given  points. 

In  both  cases  an  algebraic  expression  could  readily  be  derived 
giving  the  exact  relation  between  discharge  and  loss  of  head,  but  prac- 
tically the  problem  is  best  solved  by  determining  the  size  of  a  single 


FLOW    THROUGH  COMPOUND   PIPES.  759' 

pipe  which  shall  be  equivalent  to  the  given  combination,  that  is,  such 
a  size  as  will  give  the  same  loss  of  head  for  a  given  discharge.  The 
method  of  solution  can  best  be  explained  by  solving  two  examples. 

i  .   As  an  example  of  the  first  case  let  the   sizes  and  lengths  be  as 
given  in  Fig.  224.      To  get  the  size  ,  • 

of  a  pipe   1600  feet  long  which  will  *  ^300'  '     TOO'  - 


give   the   same   loss  of  head  for  the  FIG.  224. 

same  discharge,  assume  any  convenient  discharge,  such  as  400  gallons 
per  minute.  Then  by  the  diagram  on  page  243  we  have  the  following 
losses  of  head  : 

For  A  C,  loss  =  1  20  X   •  3  =  36    feet 
«    CD,     "     =     17  X  .5  =    8.5  « 

"    DB,     "     =  4.5  X  -8  =    3.6  " 


Total  loss  of  head  =  48. 1  feet 

The  total  loss  of  head  is  at  an  average  rate  of  30  feet  per  1000.  The 
size  which  will  discharge  400  gallons  per  minute  at  this  loss  of  head 
is  then  found  by  the  diagram  to  be  5.3  inches  in  diameter,  which  size 
can  be  substituted  for  the  given  combination  in  all  calculations  relating 
to  the  section  AB  as  a  whole. 

2.  In  the  other  case  assume  the  arrangement  shown  in  Fig.  225. 
The  problem  is  to  get  the  size  of  a  single  pipe  from  A  to  B,  equivalent 
c  ^-  D       to  the  given    combination.      Get    first, 

by  the  method  just  described,  the  size 
of  a  uniform  pipe  ACDB,  1200  feet 
long,  which  shall  be  equivalent  to  the 
pipes  A  C  D  B  as  shown.  This  size  will 
6'  be  4. 5  inches.  Now  the  loss  of  head 

FlG-  225-  between  A  and  B  must  be  the  same  by 

both  routes.  Assume  any  loss  of  head,  as  10  feet,  and  find  the  dis- 
charge by  each  route.  For  the  6-inch  pipe  the  loss  is  -^  =  16.7  feet 

per  1000  feet,  and  the  discharge  =390  gallons  per  minute.      For  the 

10 
4. 5 -inch  pipe  1200  feet  long  the  loss  is  —  —  8.33  feet  per  1000,  and 

the  discharge  =  130  gallons  per  minute.  The  total  discharge  —  520 
gallons,  and  the  size  of  pipe  600  feet  long  which  will  deliver  520 
gallons  at  a  loss  of  head  of  10  feet  is  found  to  be  about  6.7  inches, 
which  is  the  equivalent  size  desired.  If  three  or  more  pipes  extend 
from  A  to  B,  the  problem  can  be  solved  in  a  similar  manner.  Where 


6OO' 


6OO' 


';60  THE  DISTRIBUTING   SYSTEM. 

the  pipes  are  of  the  same  length  the  relative  discharges  can  be  deter- 
mined from  the  table  of  relative  capacities  on  page  758. 

In  practice  there  will  usually  be  complications  from  the  fact  that 
two  routes  may  be  connected  at  more  than  two  points,  in  which  case 
no  simple  exact  method  of  calculation  can  be  used ;  but  by  making 
certain  -reasonable  assumptions  as  to  the  direction  of  flow,  and  eliminat- 
ing some  of  the  cross-connections,  the  problem  may  be  reduced  to  the 
simple  form  just  discussed.  A  more  extended  example  is  given  on  page 
768.  In  making  assumptions  as  to  the  relative  flow  in  different  lines, 
there  should  be  kept  in  mind  the  very  great  effect  of  diameter  (about 
as  cfi)  and  the  comparatively  small  effect  of  distance  (about  as  VI). 

747.  Calculation  of  the  Pipe  System. — Before  beginning  the  calcula- 
tion of  a  distributing  system,  a  map  should  be  prepared  showing  thereon 
the  streets  where  pipes  are  required,  probable  lines  of  future  growth, 
character  of  buildings  in  various  districts,  etc.  On  the  map  can  also 
be  recorded  the  population  of  various  districts,  ordinary  rates  of  con- 
sumption, and  number  of  fire-streams  required  simultaneously  at 
different  points.  There  should  also  be  shown  on  this  map  the  desired 
hydrant  pressure  at  various  points,  referred  to  a  horizontal  plane  as 
well  as  to  the  ground-surface.  This  pressure  will  of  course  be  selected 
with  reference  to  the  head  available,  and  may  need  to  be  altered  before 
the  plans  are  finally  completed. 

In  designing  a  pipe  system  it  will  be  well  to  first  lay  out  in  a  tenta- 
tive way  certain  main  lines  of  pipes,  or  arteries,  to  supply  certain  large 
districts,  which  may  be  more  or  less  separated  by  undeveloped  territory. 
Then  it  will  be  convenient  to  determine  upon  the  size  and  arrangement 
of  the  smallest  cross-mains,  according  to  the  number  of  fire-streams 
needed  in  any  given  small  area.  The  arrangement  of  submains  feed- 
ing these  smaller  ones,  and  connections  with  the  main  arteries  and  the 
submains  in  other  districts,  can  then  be  arranged,  provision  being 
made  at  all  points  for  the  ordinary  consumption  as  well  as  the  fire 
supply.  Then,  with  a  tentative  plan,  the  maximum  number  of  fire- 
streams  should  be  assumed  in  use  at  various  points  in  the  system,  and 
the  loss  of  head  between  the  source  and  the  hydrants  in  question 
estimated  as  closely  as  practicable.  This  loss  should  not  exceed  the 
desired  limit,  and  for  economy  should  be  adjusted  in  accordance  with 
the  principles  of  the  preceding  articles.  Several  arrangements  should 
be  tried  and  comparative  estimates  made.  As  already  shown,  the 
possible  variations  in  size  will  not  be  large. 

The  calculations  involved  will  be  only  roughly  approximate,  and  to 
enable  them  to  be  made  at  all,  certain  assumptions  may  be  necessary 


CALCULATION  OF   THE  PIPE   SYSTEM. 


76l 


as  noted  in  the  preceding  article.  If  the  area  is  broad,  the  calculations 
are  much  more  difficult  than  where  it  is  long  and  narrow.  It  is  to  be 
noted  that  any  large  system  will  be  built  up  gradually,  and  will  have 
to  be  reinforced  from  time  to  time  by  additional  larger  mains  or  by 
replacing  small  ones  by  large  ones.  The  actual  loss  of  head  which 
obtains  may  then  be  known  by  actual  measurements,  and  the  effect 
of  additional  mains  can  be  quite  easily  estimated.  However,  in  laying 
out  new  systems,  and  often  in  investigations  of  old  systems,  certain 
calculations  need  to  be  made. 

748.  Calculation  of  Small  Service  Mains. — In  long  narrow  districts 
the  pipes  can  be  calculated  by  the  methods  already  described,  but 
where  the  system  covers  a  broad  area  the  problem  is  a  very  indefinite 
one.  In  such  a  case  we  will  usually  have,  as  noted  on  page  688,  a 
general  scheme  of  large  pipes  filled  in  between  with  smaller  pipes, 
forming  a  sort  of  gridiron  system. 

The  size  and  arrangement  of  the  small  mains  can  be  determined 
conveniently  by  the  following  approximate  method:  In  Fig.  226  is 
represented  a  system  of  small  cross-mains 
where  the  streets  are  250  to  300  feet  apart 
in  each  direction.  It  is  assumed  that  the 
pipes  are  fed  from  both  directions.  Sup- 
pose it  is  desired  to  concentrate  20  fire- 
streams  at  A  without  exceeding  600  feet 
of  hose,  assuming  that  the  hydrants  are 
suitably  spaced  to  render  this  possible. 
Draw  a  circle  with  a  radius  of  about  500 
feet  with  A  as  a  center.  It  will  be  found 
to  cut  fourteen  lines  of  pipe.  It  will  then 
be  approximately  correct  to  assume  these 

fourteen  lines  of  pipe  tributary  to  the  fire,  without  reference  to  the 
exact  location  of  the  hydrants.  Each  pipe  where  cut  by  the  circle  will 
then  on  the  average  have  to  supply  1.7  fire-streams,  or  420  gallons 
per  minute,  and  if  6-inch  pipes  be  used,  the  loss  of  head  at  this  point 
will  therefore  be  about  20  feet  per  1000  feet,  assuming  all  pipes  to  dis- 
charge at  the  same  rate.  This  assumption  will  be  approximately 
correct  for  a  small  area  situated  in  a  large  system  and  surrounded  by 
large  pipes,  as  the  loss  of  head  near  the  fire  will  be  much  greater  than 
at  points  more  remote.  The  loss  of  head  at  points  nearer  A  will  be  at 
a  rather  less  rate  than  at  the  given  circle,  if  the  hydrants  be  evenly 
distributed ;  and  the  loss  of  head  outside  this  circle  will  rapidly  decrease 
as  other  vertical  and  horizontal  lines  are  crossed. 


-300- 


FIG.  226. 


/02  THE  DISTRIBUTING   SYSTEM. 

If  thirty  streams  were  needed  in  the  same  area,  each  pipe  would 
have  to  supply  2.1  streams,  or  520  gallons.  If  6-inch  pipes  be  used, 
the  loss  of  head  would  be  about  28  feet  per  1000,  which  might  be  a 
greater  loss  than  desirable.  In  this  case  the  supply  could  be  furnished 
by  the  use  of  8-inch  pipes  running  one  way  and  6-inch  the  other. 
Then  at  least  six  8-inch  pipes  would  be  available,  and  eight  6-inch. 
By  the  table  on  page  758  it  is  found  that  six  8-inch  pipes  are  equiva- 
lent to  thirteen  6-inch  pipes,  hence  we  have  an  equivalent  of  twenty- 
one  6-inch  pipes,  giving  a  loss  of  head  of  about  14  feet  per  1000.  In 
this  case  every  alternate  pipe  might  perhaps  be  made  an  8-inch.  For 
still  larger  supplies  all  pipes  can  be  made  8-inch,  or  a  10-  or  1 2-inch 
pipe  placed  in  every  second  or  third  street.  In  general  it  is  somewhat 
more  economical  to  provide  volume  in  one  or  two  large  pipes  than  to 
increase  the  size  of  all,  but  care  should  be  taken  that  the  smaller  pipes 
are  not  too  long  for  the  number  of  hydrants  placed  upon  them. 

The  approximate  loss  of  head,  locally,  can  be  found  in  the  way 
described  for  any  given  arrangement,  where  the  location  is  in  the  cen- 
tral part  of  a  large  network  of  pipes  or  where  large  pipes  surround  the 
territory. 

For  residence  districts  the  blocks  are  usually  about  250  to  300  feet 
by  500  to  600  feet,  and  larger  pipes  must  be  used  to  furnish  the  same 
number  of  streams  with  the  same  loss  of  head. 

To  aid  in  estimating  the  value  of  any  particular  arrangement  of 
cross-mains,  the  approximate  number  of  fire-streams  which  may  be 
supplied  by  different  arrangements  of  pipes  at  a  loss  of  head  of  about 
10  pounds  for  the  first  1000  feet  from  the  center,  is  here  given. 

TABLE    NO.    100. 

APPROXIMATE    NUMBER    OF    FIRE-STREAMS    SUPPLIED    BY  DIFFERENT  ARRANGEMENTS 
OF    PIPES    FOR   A    LOSS    OF    HEAD    OF    IO    POUNDS    IN    FIRST    IOOO    FEET. 

Arrangement  of  Pipes.  Approximate  No. 

of  Streams. 
Blocks  300  feet  by  600  feet. 

All  4-inch 6 

4-inch  lengthwise,  6-inch  crosswise 10 

All  6-inch 20 

6-inch  lengthwise,  8-inch  crosswise 25 

All  8-inch 40 

6-inch  lengthwise,  lo-inch  crosswise 40 

6-inch  lengthwise,  12-inch  crosswise 50 

Blocks  300  feet  by  300  feet. 

All  4-inch 9 

4-inch  and  6-inch 18 

All  6  inch 25 

6-inch  and  8-inch 40 

All  8-inch 60 

6-inch  and  lo-inch 65 


CALCULATION  OF   THE   PIPE   SYSTEM.  763 

The  loss  of  head  here  considered  refers  to  the  most  centrally 
located  hydrant;  the  loss  at  other  hydrants  will  be  less.  In  many 
cases  a  considerably  larger  loss  than  here  given  would  be  permissible, 
and  the  possible  number  of  fire-streams  could  be  increased,  but  not 
often  more  than  25  per  cent. 

749.  Calculation  of  Large  Mains. — The  arrangement  of  mains  and 
submains  must  be  made  with  reference  to  the  ordinary  consumption 
as  well  as  the  fire  demand,  and  proportioned  in  accordance  with  the 
principles  already  discussed.  The  best  velocities  will  be  much  lower 
than  in  the  small  pipes.  If  nothing  but  fire  demand  existed,  an  ideal 
system  would  consist  of  a  network  of  pipes  of  the  sizes  determined  in 
the  last  article,  surrounded  by  a  large  feeder  so  as  to  maintain  a  nearly 
uniform  pressure  at  the  periphery.  The  water  could  then  be  concen- 
trated for  fire  purposes  with  the  least  loss  of  head,  and  no  other  large 
mains  would  be  required.  But  to  provide  adequate  pressure  over  large 
areas  the  ordinary  consumption  must  be  taken  account  of.  A  certain 
number  of  large  mains  will  be  required,  and  these  will  increase  in  size 
as  we  approach  the  source  of  supply.  It  is  in  these  large  mains  and 
branches  that  a  great  saving  can  be  effected  by  having  two  or  more 
reservoirs  located  at  different  points  in  the  city.  The  possibility  of  one 
of  the  large  mains  being  shut  off  in  time  of  fire  should  be  considered, 
and  the  system  so  arranged  that  the  small  mains  may  be  fed  from  two 
or  more  larger  ones. 

Let  Fig.  227  represent  a  part  of  a  large  network  of  pipes,  in  which 
the  lines  AB  arid  BC  are  at  or  near  margins  of  the  system.  With  the 
arrangement  shown  let  it  be  required  to  determine  approximately  the 
maximum  loss  of  head  between  D  and  any  other  point,  such  as  Z,  in  the 
section  EH,  and  to  adjust  the  size  of  the  large  mains.  Suppose  that 
twenty  fire-streams,  or  5000  gallons  per  minute,  are  required  in  the 
vicinity  of  Z,  and,  further,  that  the  maximum  rate  of  the  ordinary  con- 
sumption is  400  gallons  per  minute  in  each  of  the  large  divisions. 

With  twenty  fire-streams  in  action  near  Z,  the  loss  of  head  in  the 
6-inch  pipes  between  Z  and  the  surrounding  large  pipes  will  be  found 
to  be  about  10  pounds,  although  the  pressures  in  these  large  pipes  will 
vary  considerably  at  different  points.  The  line  EB  feeds  five  6-inch 
pipes,  three  of  which  are  likely  to  be  called  upon  simultaneously  to 
supply  about  two  fire-streams  each ;  hence  EB  would  have  to  supply 
about  six  streams.  From  the  table  on  page  757,  we  would  evidently 
need  about  a  12 -inch  pipe,  and  this  is  the  size  which  would  result  by 
the  application  of  the  method  of  Art.  744.  BH  will  also  be  made  a 
12-inch  pipe.  Of  the  twenty  fire-streams  demanded  at  Z,  six  or  eight 


764 


THE  DISTRIBUTING   SYSTEM. 


may  be  assumed  to  come  from  GH  together  with  the  five  6-inch  pipes 
between  GH  and  JK.  The  line  GH  will  also  partly  supply  BH,  and 
as  the  capacity  of  five  6-inch  pipes  is  not  much  more  than  one  lo-inch, 


H 


X 


\ 


\ 


/<? 


X 


3* 


H 


K 


N 
FIG.  227. 

we  may  assume  that  five  or  six  streams  will  be  carried  by  GH.      This 
line  will  then  need  to  be  again  a  10-  or  12-inch  pipe. 

Farther  away  from  Z  the  proportion  carried  by  each  large  main 
becomes  very  difficult  of  estimation.  In  the  arrangement  here  assumed 
the  small  pipes  have  about  one-half  the  capacity  of  the  large  ones, 
except  in  the  vicinity  of  D.  It  will  be  reasonable,  then,  to  design  the 
large  pipes  to  carry  two-thirds  of  the  total  required  quantity,  and  to 
provide  for  contingencies  by  assuming  at  the  same  time  one  of  the 
large  pipes  tributary  to  any  district  to  be  out  of  service.  Another 
method  which  may  be  used  is  to  assume  all  the  water  carried  by  the 
large  pipes,  leaving  the  contributions  of  the  smaller  pipes  as  a  margin 
of  safety.  Whichever  assumption  be  made,  the  approximate  loss  of 
head  in  the  large  mains  from  Z  towards  the  source  D  can  then  be 
found  in  the  same  general  way  as  employed  for  service-mains.  To  do 
this  we  may  sketch  the  lines  ab,  cd,  etc.,  across  the  system  in  such  a 
direction  that  they  will  represent,  as  nearly  as  can  be  judged,  lines  of 


CALCULATION  OF   THE   PIPE   SYSTEM. 

equal  pressure ;  then  note  the  number  and  size  of  large  mains  cut  by 
these  lines.  The  relative  flow  in  each  main  can  then  be  estimated  in 
proportion  to  its  capacity  and  the  directness  of  the  route,  and  the 
approximate  loss  of  head  per  1000  feet  determined  at  several  points, 
and  finally  the  total  loss  between  Z  and  D.  The  maximum  rate  of 
the  ordinary  consumption  should  be  taken  account  of  at  each  section. 
Very  roundabout  routes  should  be  omitted  from  the  calculation,  and  a 
margin  allowed  for  contingencies  in  one  of  the  ways  mentioned  above. 

The  loss  of  head  between  Z  and  D  may  in  the  present  case  be 
estimated  as  follows:  On  section  ab  the  rate  of  flow  is  about  5700 
gallons  per  minute,  two-thirds  of  which  is  3800  gallons.  Four  12-inch 
pipes  are  intersected,  and,  omitting  one  for  contingencies,  the  flow 
through  each  of  the  others  will  average  about  1300  gallons  per  minute, 
which  will  give  a  loss  of  head  of  about  5  feet  per  1000.  For  section 
cd  the  maximum  rate  will  be  about  6800  gallons,  with  about  four  pipes 
available  for  two-thirds  this  amount,  which  will  involve  a  loss  of  head 
of  about  3.8  feet  per  1000.  Similarly  on  section  ef  the  volume  is 
about  8500  gallons,  with  four  pipes  in  service,  giving  a  loss  of  head  of 
5.5  feet  per  1000.  On  section  gh  we  will  assume  available  for  the  total 
volume,  one  2O-inch  pipe,  one  1 6-inch,  and  seven  6-inch  pipes.  The 
volume  equals  about  9600  gallons  per  minute.  The  loss  of  head  for 
this  combination  is  about  5  feet  per  1000.  Farther  towards  D  the 
supply  may  be  assumed  to  come  through  the  2O-inch  pipe  and  one 
1 6-inch,  which  will  also  give  about  5  feet  loss  of  head  per  1000  feet. 
In  the  24-inch  supply-pipe,  with  a  rate  of  98,000  gallons  per  minute, 
the  loss  of  head  would  be  about  6  feet  per  1000. 

Considering  the  average  distance  traveled  from  section  to  section, 
assuming  blocks  300  by  600  feet,  the  actual  loss  of  head  from  ab  to  cd 
is  approximately  8  feet,  from  cd  to  ef  8.5  feet,  from  efto  gh  5  feet, 
and  from  gh  to  D  4.5  feet.  Adding  the  loss  of  head  in  the  small  pipes 
and  mains  near  Z,  we  find  a  total  loss  of  head  of  50  to  55  feet,  or 
about  23  pounds,  which  would  ordinarily  be  a  reasonable  allowance. 

With  a  reservoir  at  A, 'or  beyond,  nearly  all  the  12 -inch  submains 
could  readily  be  reduced  to  lO-inch  or  8-inch  pipes,  or  perhaps  most 
of  them  to  6-inch.  The  volume  flowing  through  any  pipe  would  be 
reduced  about  one-half,  and  the  distance  traveled  also  about  one-half, 
thus  reducing  the  loss  of  head  very  greatly.  A  large  main  of  about 
20  inches  in  diameter,  extending  from  pumps  to  reservoir,  would, 
however,  be  required. 

750.  Example. — In  Fig.  228  is  shown  a  possible  arrangement  of  pipes  and 
hydrants  to  meet  the  conditions  stated  on  page752  ai*d  in  Table  No.  101. 


THE  DISTRIBUTING  SYSTEM. 


CALCULATION  OF  THE  PIPE  SYSTEM. 


767 


A  considerable  use  is  made  of  4-inch  pipe,  as  experience  has  shown  that  well' 
coated  pipe  will  corrode  very  slowly  with  the  Madison  water.     The  fire-pres- 

TABLE   NO.   101. 

ESTIMATED   POPULATION,   AND   MAXIMUM    ORDINARY  AND   FIRE-RATES   FOR 
DIFFERENT   DISTRICTS   OF   FIG.    228. 


District. 

Estimated 
Future 
Population. 

Maximum 
Ordinary  Rate, 
Gallons  per 
Minute. 

Maximum 
Fire-  rate, 
Gallons  per 
Minute. 

Total  Maxi- 
mum Rate, 
Gallons  per 
Minute. 

j 

•7QOO 

•?4o 

2  

800 

QO 

2OQO 

7.  . 

•3400 

2Qo 

800 

lOQO 

4  

•3  CQO 

•?,OO 

2  COO 

2800 

c    . 

2500 

2'7O 

2  COO 

6  :::::." 

C7OO 

460 

2  COO 

2Q6o 

7  

•?4.OO 

•3QO 

I2OO 

I  Coo 

8  

•34.00 

-?oo 

I2OO 

I  Coo 

g.  . 

1600 

I4O 

800 

040 

io  

4  Coo 

•3QO 

2  COO 

2890 

Entire  city  .  .  . 

32300 

2830 

3750 

6580 

m 
b 

r*                                                           s*" 

m                          *                   r?               &          o 

p 

8" 

Pumping  P/ant*    $"                                            \ 

a 

r     <3" 
^ 

i 
1 

I 
&' 

t> 

>\«                         4" 

^>v^                      £"     ft                         & 

9                                    4" 

B 


FIG.  229.         j  4* 

sure  at  the  pumping-station  is  assumed  to  be  120  pounds,  and  the  pipes  made 
of  such  size  that  the  loss  of  head  to  the  most  remote  hydrant  will  not  exceed 


;68 


THE  DISTRIBUTING   SYSTEM. 


40  pounds.     The  ground  is  assumed  to  be  level.      Many  other  arrangements 
could  be  made,  some  of  which  might  be  more  economical  than  that  given. 

As  a  further  example  of  the  application  of  the  method  of  calculation  given 
in  Art.  746,  page  758,  we  will  here  compute  the  approximate  loss  of  head 
from  the  pumping-station  A,  Fig.  228,  to  the  point  J3,  where  it  is  assumed 
that  eight  fire-streams  are  in  use.  We  will  for  the  present  neglect  the  ordinary 
consumption  and,  to  make  the  solution  possible,  will  omit  certain  cross-lines 
and  modify  the  arrangement  as  shown  in  Fig.  229.  We  will  also  estimate 
that  the  various  pipes  from  a  to  b  are  equivalent  to  a  single  1 2-inch  pipe. 
The  problem  is  to  determine  the  loss  of  head  from  the  pumps  to  the  point  / 
by  finding  the  size  of  a  single  pipe  which  will  be  equivalent  to  the  system 
shown.  The  blocks  of  Fig.  228  are  assumed  to  be  600  feet  long  by  300  feet 
wide.  Beginning  with  the  loop  hki  we  first  find  a  single  pipe,  hi,  equivalent 
to  the  two  pipes  shown,  then  a  single  pipe  ef  equivalent  to  the  given  pipe  ef 
together  with  the  new  pipe  egif  just  found,  etc.  The  calculations  are  very 
quickly  made  as  shown  in  Art.  746.  The  results  in  detail  are  as  follows: 

Equivalent  Pipes.- 


Line. 

hi 
hjki 

Diameter. 
6 
4 

Length. 
I2OO  ) 
I800  ) 

Line. 
hi 

Diameter. 
6-5 

Length, 
I2OO 

egh 

6 

1870  j 

Equiv. 

hi 

6. 

5 

I2OO  > 

ehf 

6. 

7 

3370 

if 

6 

300) 

Equiv. 

ehf 
<f 

6. 

4 

2 

3370} 
3000  f 

ef 

6. 

7 

30CO 

ce 

6 

370  J 

Equiv. 

ef 

6. 

7 

3000  V 

cefd 

6. 

5 

3670 

fd 

6 

300) 

Equiv. 

cd 
cefd 

8 
6. 

5 

3600  ) 
3670  j" 

cd 

9- 

5 

3600 

ab 

12 

t 

1  800  "j 

Equiv. 

be 
cd 

10 

9- 

5 

980! 
3600  j 

abl 

9- 

4 

7880 

dl 

8 

iSooJ 

nqp 
nop 

6 
6 

3300  ) 

2100  J 

np 

7- 

4 

2IOO 

amn 

6 

3000  J 

Equiv. 

np 

7- 

4 

2100  I 

ans 

6. 

4 

5400 

ps 

6 

300  ) 

Equiv. 

ans 

ars 

6. 

8 

4 

5400  | 
4800  J 

as 

9- 

3 

4800 

Equiv. 

as 
si 

9- 

8 

3 

4800  )' 
300  j 

asl 

9- 

2 

5100 

Equiv. 

abl 

9- 

4 

7880  | 

Equiv. 

asl 

9- 

2 

5100  j" 

al 

ii. 

3 

5100 

Thus  the  system  all  is  equivalent  to  a  single  pipe  9.4  inches  in  diameter 
and  7880  feet  long,  and  the  system  asl  is  equivalent  to  a  9.2-inch  pipe  5100 
feet  long.  Finally,  these  two  are  found  to  be  equivalent  to  a  single  pipe  1 1.3 
inches  in  diameter  and  5100  feet  long.  The  loss  of  head  in  such  a  pipe, 
for  eight  streams  of  250  gallons  each,  would  be  13.6  feet  per  1000,  or  a  total 
loss  of  about  70  feet  or  30  pounds.  The  volume  carried  by  the  system  abl 


SEPARATE   SERVICES  FOR  DIFFERENT  ELEVATIONS.         769 

will  be  equal  to  that  which  would  be  carried  by  a  9.4-inch  pipe  7880  feet 
long,  with  a  loss  of  head  of  70  feet.  This  will  be  about  900  gallons  per 
minute.  The  volume  carried  by  the  other  system  will  be  1160  gallons  per 
minute.  Corrections  can  be  approximately  made  for  the  amounts  consumed 
locally  by  adding  such  amounts  to  the  above  quantities  at  a  few  points  along 
the  pipe  system. 

751.  Separate  Services  for  Different  Zones  of  Elevation — Where  the 
different  parts  of  a  town  vary  considerably  in  elevation,  it  is  frequently 
advisable  to  divide  the  distributing  system  into  two  or  more  independ- 
ent portions,  each  serving  an  area  or  zone  situated  between  certain 
limiting  elevations.  It  often  happens  that  only  a  small  portion  of  a 
city  is  at  a  high  elevation,  and  by  thus  separating  the  systems  of  dis- 
tribution a  comparatively  small  amount  of  water  will  need  to  be  raised 
to  the  maximum  height,  the  greater  portion  being  pumped  against  a 
much  lower  pressure.  By  this  arrangement  a  large  saving  can  be 
effected  in  the  expense  of  pumping,  and  the  use  of  excessive  pressures 
in  the  lower  districts  will  also  be  avoided. 

Various  arrangements  may  be  made  for  supplying  the  different 
zones.  Each  zone  may  be  practically  an  independent  system,  with  its 
own  pumping-station  and  perhaps  its  own  source  of  supply;  or  the 
pumps  of  a  higher  zone  may  be  supplied  by  a  reservoir  located  at  a 
high  point  in  the  next  lower  zone ;  or  the  pumps  of  the  different  zones 
may  all  be  located  at  the  same  station  and  obtain  their  supply  from 
the  same  source.  In  the  gravity  system  a  division  is  often  made  so 
that  the  lowest  zone  is  supplied  by  gravity,  while  the  upper  zones  are 
supplied  by  pumps.  The  most  favorable  arrangement  will  be  deter- 
mined chiefly  by  the  cost  of  operation  and  the  cost  of  the  necessary 
piping.  For  small  plants  separate  pumping-stations  would  rarely  be 
an  economical  arrangement.  Separate  pumps  placed  in  the  same 
station  would  probably  be  employed ;  or,  where  the  difference  in  pres- 
sure is  not  great,  the  same  pump  may  be  designed  to  supply  the  two 
services  alternately.  The  latter  arrangement  will  require  some 
storage  capacity  in  each  system. 

The  advantage  of  two  or  more  services  depends  largely  on  how 
great  a  proportion  of  the  supply  can  be  furnished  at  the  lower  pressure. 
If  any  considerable  amount  of  storage  is  provided  in  the  higher  of  two 
systems,  advantage  may  be  taken  of  this  to  furnish  water  at  a  high 
pressure  for  fire  purposes  in  the  lower  system.  For  this  purpose,  con- 
nections controlled  by  suitable  valves  should  be  made  between  the  two 
systems  at  one  or  more  points.  If  the  lower  system  contains  a  reser- 
voir, it  can  be  shut  off  in  the  same  way  as  described  for  stand-pipes 
(page  719). 


770  THE   DISTRIBUTING   SYSTEM. 

Separate  systems  for  different  pressures  have  a  disadvantage  in  the 
fact  that  at  their  margins  the  two  networks  of  pipes  are  not  connected, 
and,  as  a  result,  somewhat  larger  pipes  are  required  for  the  same 
efficiency  than  in  the  single  system. 

752.  Location  of  Pipes  and  Valves. — The  distributing-pipes  should 
be  so  located  with  respect  to  street  lines  as  to  be  readily  found  and  to 
avoid  other  structures  as  far  as  practicable.      The  center  of  the  street 
being  usually  reserved  for  the  sewer,    the  water-pipes   are  placed  at 
some  fixed  distance,  usually  from  5  to   10  feet,  from  the  center.      The 
side  chosen  should  be  the  same  throughout.      The  north  side  of  east 
and  west  streets  will  be  warmer  than  the  south  side. 

Valves  should  be  introduced  in  the  system  at  frequent  intervals  so 
that  comparatively  small  sections  can  be  shut  off  for  purposes  of 
repairs,  connections,  etc.  As  a  general  rule,  wrherever  a  small  pipe 
branches  from  a  large  one,  the  former  should  be  provided  with  a  valve. 
Thus  with  10-  or  1 2-inch  pipes  feeding  6-inch  pipes,  each  of  the  latter 
should  have  a  stop-valve  at  each  end.  At  intersections  of  large  pipes 
a  valve  in  each  branch  is  usually  desirable.  In  a  network  of  small 
pipes  of  uniform  size,  a  valve  in  each  line  at  each  intersection,  or  four 
in  all,  is  rather  more  than  necessary,  but  two  at  each  intersection,  or  a 
valve  in  each  line  every  two  blocks,  answers  very  well.  The  map 
of  Fig.  228  shows  a  suitable  arrangement  of  valves  for  the  case  in 
question. 

Valves,  like  pipe-lines,  should  be  located  systematically.  They 
are  usually  located  in  range  either  with  the  property-line  or  the  curb- 
line,  but  sometimes  are  placed  in  the  cross-walks.  A  form  of  three- 
way  and  four-way  valve,  placed  at  the  intersection  of  two  pipes,  has 
been  used  to  some  extent.  This  arrangement  reduces  the  number  of 
valve-boxes  and  is  reported  to  be  quite  satisfactory. 

753.  Hydrants. — The  general  location  of  hydrants  has  already  been 
considered  in  Art.  741.      In  fixing  upon  the  exact  location,  and  the 
side  of  the  street  on  which  each  should  be  placed,  a  detailed  examina- 
tion should   be   made  and  the   location   determined   with  reference  to 
important    buildings,    convenience    of  access    in    case    of    fires,    etc. 
Generally  the  hydrant  is  placed  on  the  same  side  of  the  street  as  the 
pipe,  and   is  connected  to  the   larger  of  two   pipes   where  there  is  a 
choice. 

Hydrants  are  of  two  general  types :  the  post  hydrant,  in  which  the 
barrel  of  the  hydrant  extends  2  or  3  feet  above  the  ground-surface, 
and  the  flush  hydrant,  in  which  the  barrel  and  nozzle  are  covered  by 
a  cast-iron  box  flush  with  the  surface.  The  former  is  more  commonly 


HYDRANTS. 


77i 


used,  and  as  it  is  much  more  readily  found  and  more  conveniently 
operated,  it  is  to  be  preferred,  except  perhaps  in  the  congested  districts 
of  large  cities,  or  on  narrow  streets  where  all  obstructions  should  be 
avoided.  Post  hydrants  are  set  just  back  of  the  curb-line;  flush 
hydrants,  either  in  the  sidewalk  or  in  the  street.  In  Boston  and  some 
other  Eastern  cities,  extensive  use  is  made  of  a  flush  hydrant  placed 
directly  over  the  main,  or  at  the  intersection  of  two  mains. 

The  branch  supplying  the  hydrants  should  be  of  a  size  correspond- 
ing to  the  number  of  streams  to  be  carried,  and  should  be  designed  on 
the  same  principle  as  other  pipes.  For  one  fire-stream  the  branch 
may  be  4-inch,  and  for  two  streams  6-inch,  etc.  The  hydrant-barrel 
should  be  nearly  as  large. 

Many  styles  of  hydrants  are  on  the  market,  most  of  which  will  give 
reasonably  good  service  if  properly  handled.  Reliability  of  operation 
is  the  first  essential,  but  next  in  importance  is  the  requirement  that  the 
frictional  loss  in  the  hydrant  shall  be  small.  All  waterways  should 
be  ample,  and  sharp  angles  and  sudden  changes  in  size  should  be 
avoided  as  much  as  possible.  Considerable  difference  exists  in  differ- 
ent hydrants  in  this  respect,  with  a  corre- 
sponding difference  in  the  amount  of 
pressure  lost.*  The  main  valve,  which 
is  located  at  the  base  of  the  hydrant, 
should  seat  accurately  and  remain  tight, 
and  when  open  should  provide  ample 
waterway.  Valve-stems  should  be  made 
of  extra  strength,  as  they  are  likely  to  be 
subjected  to  rough  usage.  Valve  and 
stem  should  be  removable  without  the 
necessity  of  digging  up  the  hydrant.  In 
Fig.  230  are  shown  two  forms  of  hydrants 
which  illustrate  the  two  general  types  of 
valves  used, — the  gate- valve  and  the 
compression-valve.  Small  independent 
valves  controlling  the  nozzles  are  useful  in 
multiple-nozzle  hydrants,  as  they  enable 
hose-connections  to  be  more  conveniently 
made.  In  ordering  hydrants  care  should 
be  taken  to  have  the  nozzles  of  the  same 
standard  as  those  used  in  adjoining  large  FIG.  230. — FIRE-HYDRANTS. 


*  See  results  of  experiments  on  hydrants  by  Newcomb  in  Trans.  Am.  Soc.  M.  E., 
1899,  xx.  p.  494. 


7/2  THE  DISTRIBUTING   SYSTEM. 

cities,  so  that  connections  can  readily  be  made  to  fire  apparatus  which 
may  be  borrowed  in  emergencies. 

When  a  hydrant  is  closed  after  use,  the  water  remaining  in  the 
barrel  must  be  drained  out  through  a  drip,  so  arranged  as  to  open 
when  the  main  valve  is  closed.  This  is  an  important  feature  of  the 
design,  as  a  hydrant  is  likely  to  freeze  if  not  thoroughly  drained.  The 
escaping  water  may  be  led  away  through  a  small  drain-pipe  to  a 
sewer,  or  a  considerable  body  of  broken  stone  and  gravel  may  be  filled 
around,  the  base,  into  which  the  water  may  be  allowed  to  drain.  If 
the  hydrant  base  is  below  ground-water  level,  the  drip  should  be 
plugged  and  the  hydrant  pumped  out  after  use.  Hydrants  are  fre- 
•quently  provided  with  an  outside  shell  or  frost-case,  but  the  use  of  this 
lias  been  found  of  little  advantage.  In  setting  hydrants  care  should 
be  taken  to  provide  a  firm  base  and  to  ram  solidly  back  of  the  barrel. 
The  hydrant  branch  should  be  covered  at  least  as  deep  as  the  main, 
as  this  branch  is  essentially  a  dead  end  and  is  much  more  likely  to 
freeze  than  the  main  itself. 

754.  Depth  of  Covering  for  Distributing-pipes. — In  constructing  the 
pipe  system  one  of  the  most  important  points  to  settle  is  the  depth  at 
which  the  pipes  should  be  laid.      In  warm  climates  a  covering  of  2  to 
3   feet  is  sufficient.      In  cold  climates  the  depth  to  be  adopted  is  that 
which   will   be   sufficient   to   prevent   freezing.      In  the   Northwestern 
States  the  common  practice  of  a  depth  of  5  to  6  feet  proved  insufficient 
during  the  severe  winter  of  1 898-9,  and  many  small  mains  as  well  as 
service-pipes  froze.     The  experience  at  that  time  indicated  that  in  this 
region  7  feet  should  be  about  the  minimum  for    small  pipes.      In  a 
general  way  it  may  be  stated  that  in  New  York  and  New  England  the 
depth  of  cover  should  be  4  to  5  feet  for  latitude  42°,  and  6  to  7  feet  for 
latitude  45°.      Between  Lake  Michigan  and  the  Rocky  Mountains  the 
corresponding  minimum  depths  should  be  not  less  than  the  larger  of 
these  figures.      In  sandy  soil  the  depth  should  be  a  maximum.      Large 
pipes  are  not  likely  to  freeze,  but  should  be  placed  at  about  the  same 
depth  as  the  smaller  pipes  to  aid  in  maintaining  the  water  above  a 
freezing  temperature. 

755.  Service  Connections. — Service-pipes  are  usually  from  f  inch  to 
I   inch  in  diameter.      The  question  of  the  most  suitable  material  for 
these  pipes  has  been  discussed  in    Chapter  XXIV.      In  making  the 
connection  between  service-pipe  and  main,  the  latter  is  tapped  and  a 
brass    "corporation"   cock  screwed  in.      This    cock    is  then   usually 
connected  to  the  service-pipe  by  means  of  a  goose-neck,  or  U-shaped 
piece  of  lead   pipe,    in   order   to   avoid   breakage   from   settlement  of 


SPECIAL  FIRE-PROTECTION  SYSTEMS.  773 

main,  although  this  detail  is  omitted  by  some,  with  apparently  no 
bad  results.  At  the  curb  is  usually  placed  another  stop-cock,  with 
a  suitable  valve-box,  at  which  point  the  supply  to  the  consumer  is 
controlled.  Service  connections  can  be  made  without  shutting  off  the 
water,  by  the  use  of  special  tapping-machines,  several  of  which  are  oa 
the  market. 

756.  Other  Details.  —  In  laying  out  lines  of  pipe,  small  depressions 
should  be  avoided,  but  as  a  rule  the  line  may  follow  the  street  grade 
closely.     Hydrants  can  usually  be  placed  at  low  and  high  points  and 
thus  can  act  in  a  measure  as  blow-offs  for  clearing  out  sediment,  and 
as  air-valves.     For  draining  large  mains,  small  drain-pipes   connecting 
with  the  sewer  should  be  constructed  at  the  lower  points  of  the  system. 

The  construction  of  the  pipe-lines  has  already  been  described  in 
Chapter  XXV.  Where  pipes  are  laid  in  city  streets,  special  care  must 
be  taken  in  backfilling  and  replacing  the  pavement.  There  is  a  wide 
difference  of  opinion  as  to  the  best  method  of  backfilling,  but  probably 
the  most  certain  way  of  getting  the  earth  back  without  trouble  from 
future  settlement  is  by  very  thorough  ramming  of  the  material  in  a 
moist  condition,  but  not  wet.  Such  thorough  ramming  is  difficult  to 
secure,  and  it  will  usually  be  advisable  to  adopt  the  method  of  backfill- 
ing through  a  good  depth  of  water.  Hydrants  are  often  deranged  by 
being  used  for  filling  sprinkling-carts.  It  is  much  preferable  to  provide 
water-cranes  for  this  purpose,  numerous  forms  of  which  are  on  the 
market. 

757.  Special  Fire-protection  Systems.  —  Special    high-pressure  fire- 
protection    systems   were    constructed    in    a    few   cities,    conveniently 
located,  previous  to  1900,  but  since  that  time  this  method  of  improving 
the  fire  protection  has  been  given  much  attention  and  has  been  adopted 
in  several  of  the  largest  cities  of  the  country.     Very  high  pressures  can 
profitably  be  used  in  these  systems,  a  common  value  being  300  pounds 
per  square  inch.     The  pipe  system  should  be  of  ample  size  and  must 
be    designed  with  especial  reference   to  the   high   pressure   employed. 
Joints  are  commonly  hub  and  socket  pattern,  but  with  especially  deep 
sockets  and  double  grooves  for  the  lead  packing.     Specials  for  sharp 
angles  may  well  be  made  of  steel  castings.     Hydrants  must  be  of  ample 
size  and  no  connections  other  than  to  hydrants  should  be  allowed. 

Originally  these  special  fire  systems  were  laid  so  as  to  be  fed  from 
fire- boats  stationed  along  the  water  front.  These  boats  are  in  general 
use  in  large  cities  for  fighting  fires  along  the  shore  and  among  the 
shipping,  and  by  laying  special  lines  of  pipe  of  comparatively  short 
length,  they  can  be  made  of  great  use  in  fighting  fires  farther  inland 


774 


DISTRIBUTING  SYSTEM. 


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RECORDS  AND  MAPS*  775 

They  are  usually  of  large  capacity,  —  equal  to  from  ten  to  thirty  fire- 
engines,  —  and  so  can  supply  very  large  and  efficient  fire-streams.  By 
means  of  telephonic  or  telegraphic  communication,  one  fire-boat  can 
serve  any  one  of  several  pipe-lines.  Connections  between  boat  and 
pipe-line  are  made  by  means  of  several  lines  of  hose.  Generally  such 
lines  are  emptied  after  fires  and  consequently  must  be  provided  with 
ample  air  and  waste  valves,  and  often  with  relief  valves. 

The  increasing  importance  of  high-pressure  systems  has  led  to  their 
adoption  in  many  places  independently  of  fire-boat  service,  and  special 
pumping-stations  are  provided  for  supplying  the  necessary  water.  For 
such  purposes  gas  or  electricity  will  usually  be  the  most  convenient 
motive  power  and  the  triplex  or  multiple-stage  turbine  pump  the  best 
form  of  pump. 

Table  No.  102  gives  general  data  of  special  fire  systems  in  21 
cities  of  the  United  States  taken  from  a  report  on  an  auxiliary  high 
pressure  water  supply  for  Hartford,  Conn.* 

In  the  Hartford  plan  the  length  of  hose  necessary  was  given  more 
weight  than  the  probable  height  of  buildings.  The  system  was  planned 
to  limit  the  general  hose  length  to  600  feet,  and  to  400  feet  in  the  case 
of  the  more  important  city  blocks.  A  pressure  of  300  pounds  was 
adopted.  The  plans  provide  for  10.12  miles  of  8  to  24-in.  cast-iron  pipe 
ranging  in  thickness  from  j£  to  I  j4  inches,  and  giving  factors  of  safety 
of  15.3  to  10.8.  The  valves  are  to  be  of  the  double-disk  type,  tested  to 
500  pounds  per  square  inch.  The  fire-hydrants  are  of  the  gate  type 
with  four  2^-inch  outlets  and  8-inch  barrels.  The  hydrant  spacing  is 
fixed  at  150  feet  in  the  congested  district,  decreasing  to  200  feet  and 
finally  to  300  feet.  For  data  relating  to  other  plants  see  numerous 
references  at  the  end  of  the  chapter. 

Where  salt  water  is  used  in  such  systems,  special  care  must  be  taken 
in  the  design  of  valves,  etc.,  to  avoid  the  combination  of  dissimilar 
metals  without  insulation  of  rubber  or  other  like  material.  Otherwise 
galvanic  action  will  be  set  up  and  rapid  corrosion  will  result.  Besides 
this  feature,  and  the  slightly  increased  rate  of  corrosion  of  pipes,  there 
is  no  objection  to  the  use  of  salt  water. 

758.  Records  and  Maps. —  All  constructive  features  pertaining  to  the 
distributing  system  should  be  carefully  recorded  on  maps  of  adequate 
size  and  suitably  indexed.  The  exact  location  of  pipes,  hydrants,  and 
valves  is  of  special  importance.  It  will  be  convenient  to  have  two  sets 
of  maps  for  this  purpose :  one  on  a  small  scale  showing  arrangement 


See  abstract  in  Eng.  News,  1907,  LVIII,  p.  53. 


776  THE  DISTRIBUTING  SYSTEM. 

and  size  of  piping  and  points  of  connection,  and  a  set  of  large-scale 
maps,  each  one  showing  a  comparatively  small  section  of  the  system, 
on  which  the  detailed  information  can  be  recorded.  It  is  of  the  greatest 
importance  that  valves  on  large  mains  be  quickly  accessible  in  order  that 
great  damage  may  be  prevented  in  case  of  breakage  and  also  to  facilitate 
repairs.  Rigid  discipline  and  constant  drill  of  employees  is  of  great 
value  in  this  connection. 


LITERATURE. 

1.  Freeman.     The  Arrangement  of  Hydrants  and  Water-pipes  for  Protection 

of    a  City  against    Fire.     Jour.  New  Eng.  W.  W.  Assn.,  1892,  viz. 
pp.  49,  152. 

2.  Fanning.     Distributing-mains  and  Fire-service.     Proc.  Am.  W.  W.  Assn., 

1892,  p.  88;  Eng.  News,  1892,  xxvin.  p.  42. 

3.  Report  of  the  Boston  Water  Board,  1893,  contains  extracts  of  a  valuable 

report  by  Dexter  Brackett  on  fire  protection  in  various  large  cities. 

4.  Brackett.     Capacity  of  Steam  Fire-engines,  Hydrants,  and  Hose.     Jour. 

New  Eng.  W.  W.  Assn.,  1895,  ix.  p.  151. 

5.  Weston.     The  Separate  High-pressure  Fire-service  System  of  Providence, 

R.  I.     Jour.  New  Eng.  W.  W.  Assn.,  1898,  xin.  p.  85;  Eng.  News, 
1898,  xxxix.  p.  196. 

6.  Crowell.     Report  on  an  Auxiliary  Salt-water  Supply  for  Fire-protection, 

Street-washing,  Sewer-cleaning,  and  Other  Purposes.     Made  to  the 
Merchants'  Assn.,  N.  Y.     Eng.  Record,  1898,  xxxvu.  p.  124. 

7.  The  Record    System  of  the  Water-works  Department,  Detroit.      Eng. 

Record,  1898,  xxxvu.  p.  230. 

8.  Newcomb.     Experiments  on  Various  Types  of  Hydrants.     Trans.  Am. 

Soc.  M.  E.,  1899,  xx.  p.  494. 

9.  Crowell.     Report  to  the   Merchants'  Association  of  New  York  City  on 

Auxiliary  Salt-water  Supply.      1900. 

10.  Burns.     Some   Economic   Features    of    Municipal    Engineering.       Eng. 

Record,  1902,  XLV.  p.  126. 

11.  Trautwine.     Fire  Mains.     Refers  particularly  to  the  system  introduced 

in  Philadelphia.     Proc.  Engrs.'  Club  of  Philadelphia,  January,  1903. 

12.  Codman.     Philadelphia  High-pressure  Fire  Service.     Proc.  Engrs.'  Club 

of  Philadelphia,  January,  1903. 

13.  Hopson.       Pressure    in   City   Water-works  from    Fire-protection  View- 

point.    Eng.  Record,  1905,  LII.  p.  212. 

14.  The  Use  of  Salt  Water  for  Fire  Protection  and  Other  Purposes  at  U.  S. 

Navy  Yards.     Eng.  News,  1905,  LIU.  p.  109. 

15.  Ledoux.     An    Automatic    Regulating   Valve   for    Reservoirs    or    Stand- 

pipes  Supplied  from  a  Higher  Elevation.      Eng.  News,  1905,  LIII. 
P.  253. 

1 6.  A  High-pressure  Water  System  at    Coney   Island,  N.  Y.     Eng.  Record, 

1905,  LI.  p.  582. 

17.  High-pressure    System   for    Fire    Service.        Report    of    Committee    of 

National  Fire  Protective  Assn.     Eng.  Record,  1905,  LI.  p.  626. 


LITER  A  TURE,  77  7 

18.  de  Varona.      Proposed  High- pressure  Fire  System  for  the  Borough  of 

Manhattan,   New   York.      Eng.   News,  1905,  LIII.    p.    317  ;    Eng. 
Record,  1905,  LI.  p.  343. 

19.  Underwriters'   Committee  of  Twenty  on  Fire  Protection  in  New  York, 

Chicago,  and  Detroit.     Eng.  News,  1906,  LV.  p.  459. 

20.  Proposed    Auxiliary   High-pressure  Fire    Protection    Water   Supply  for 

Hartford,  Conn.     Eng.  News,  1907,  LVIII.  p.  53. 

21.  The  New  York  City  Fire  Protection  Water  System.     Eng.  Record,  1908, 

LVJI.  p.   22. 


CHAPTER   XXIX. 
OPERATION    AND    MAINTENANCE. 

759.  Conduits  and  Pipe-lines.  —  The  maintenance  of  conduits  and 
large  pipe-lines  involves  chiefly  the  work  of  cleaning  and  repairing. 
The  various  special  structures  should  be  frequently  inspected  to  detect 
any  sign  of  weakness,  and  in  the  case  of  large  aqueducts  the  entire  line 
should  be  regularly  patrolled.  Exposed  masonry  will  need  occasional 
repointing,  and  at  points  of  excessive  wear  may  need  renewal  at 
intervals.  The  right-of-way  should  be  properly  taken  care  of,  and 
slopes  of  earthen  embankments  kept  in  good  form.  Culverts  and 
other  waterways  must  be  looked  after  to  see  «that  they  are  not 
obstructed.  Air-valves  of  pipe-lines  must  be  frequently  inspected  and 
be  kept  in  working  order  ;  other  valves  require  less  frequent  inspection. 
If  the  water  carries  sediment  and  has  a  low  velocity,  the  pipe-line 
should  be  occasionally  flushed  by  opening  the  blow-off  valves.  Gates 
at  terminal  points  and  at  intermediate  reservoirs  require  frequent 
adjustment  to  regulate  the  flow  in  accordance  with  the  demand.  A 
telephone  or  telegraph  line  is  almost  indispensable  in  the  operation  of 
a  long  conduit. 

Masonry  conduits  are  likely  to  become  coated  with  slime  and 
organic  growth,  which  will  cause  a  large  diminution  of  their  carrying 
capacity,  and  if  allowed  to  remain  may  affect  the  quality  of  the  water. 
In  such  a  case  the  aqueduct  should  be  cleaned  regularly  once  or  twice 
a  year,  or  at  longer  intervals,  depending  on  the  rapidity  of  the  accumu- 
lations. In  cleaning  the  aqueduct  it  is  emptied  and  then  swept  with 
brushes  and  scrapers,  or  the  work  may  be  done  by  mechanical  brooms 
mounted  on  cars,  as  was  at  one  time  the  practice  with  the  Sudbury 
aqueduct.  Experiments  made  on  this  aqueduct,  and  also  on  the  new 
Wachusett  aqueduct  of  Boston,  show  that  the  carrying  capacity  is  in 
each  case  reduced  about  10  per  cent  by  a  few  months'  accumulation 
of  slime.  The  original  capacity  is  very  nearly  restored  by  the  cleaning 
which  the  aqueducts  regularly  receive.* 

*  See  paper  by  Patch  in  Eng.  News,  1902,  XLVII.  p.  488,  for  diagrams  showing 
effect  of  growths  on  capacity  of  aqueducts. 

778 


CONDUITS  AND    PIPE-LINES. 


779 


Cleaning  and  repairing  should  be  done,  if  possible,  at  a  favorable 
season,  so  as  to  render  the  risk  of  an  interruption  in  the  supply  as 
small  as  may  be.  In  a  well-constructed  aqueduct  or  pipe-line  the 
expense  of  repairs  should  be  very  slight. 

Large  steel  and  cast-iron  pipe-lines  will  rarely  need  to  be  emptied 
for  cleaning;  but  in  some  cases  accumulations  of  organic  growth  have 
formed,  which  greatly  obstructed  the  flow  and  which  could  not  be 
removed  by  blowing  off.  In  such  a  case  the  pipe  should  be  cleaned 
in  the  same  way  as  a  masonry  structure,  or  by  the  use  of  mechanical 
scrapers  as  described  below.  The  tuberculation,  which  occurs  to  a 
greater  or  less  extent  from  the  corrosion  of  the  iron,  often  seriously 
reduces  the  carrying  capacity  of  the  pipe.  The  removal  of  such 
incrustation  will  restore  a  large  part  of  the  lost  capacity,  and  may  be 
a  much  more  economical  method  of  increasing  the  pressure  in  a  system 
than  by  adding  new  pipes. 

760.  Use  of  Mechanical  Scrapers  in  Cleaning  Small  Pipes. — A 
method  of  cleaning  cast-iron  pipes  which  has  been  used  extensively  in 


Cross  Section. 


9  -  inch     Sc  race  r. " 
FIG.  231. — PIPE-SCRAPER. 

(From  Engineering  News,  vol.  XLIV.) 

England,  and  at  a  few  points  in  the  United  States  and  Canada,  is  by 
the  use  of  mechanical  scrapers  propelled  by  the  water-pressure.  These 
have  been  employed  chiefly  to  remove  hard  incrustation,  but  a  similar 
device  can  be  used  for  removing  less  resistant  obstructions.  The 
general  form  of  such  scrapers  is  shown  in  Fig.  231,  an  illustration  of 
one  recently  used  at  Torquay,  England.*  It  consists  of  a  scraping 

*  See  paper  by  Wm.  Ingham  before  Inst.  M.  E.  Abstract,  Eng.  News,  1900, 
XLIV.  p.  154.  The  paper  also  contains  a  description  of  a  mechanical  brush  for 
removing  peaty  deposits. 


7^0  OPERATION  AND   MAINTENANCE. 

mechanism  fastened,  by  means  of  a  jointed  rod,  in  front  of  two  propelling- 
pistons  which  are  rigidly  connected  together.  The  scraping-blades 
are  held  against  the  pipe  by  heavy  springs.  The  scraper  is  introduced 
into  the  pipe  through  a  long  hatch-box,  or  through  an  opening  made 
by  removing-  a  section  of  pipe.  After  closing  the  pipe  a  blow-off  valve 
is  opened  at  a  point  in  advance,  and  the  scraper  is  pushed  along  by 
the  water.  The  apparatus  may  be  followed  by  the  noise  it  makes,  and 
this  should  be  done  in  order  to  locate  it  if  it  should  stick.  The  velocity 
can  be  regulated  by  the  blow-off  valve.  At  Torquay  such  an 
apparatus  was  used  as  early  as  1866  in  cleaning  an  uncoated  cast-iron 
pipe.  The  operation  is  now  carried  out  at  that  place  every  year. 
The  scraper  here  described  will  pass  around  a  curve  of  a  radius  equal 
to  about  fifteen  times  the  pipe  diameter.  The  cost  of  cleaning  9-  and 
lo-inch  pipes,  at  Torquay,  was,  for  labor  alone,  $3.50  per  mile. 

Scrapers  similar  to  the  one  here  described  have  been  used  at 
Halifax  since  1880,  certain  mains  at  that  place  being  cleaned  twice  a 
year,  on  account  of  the  necessity  of  reducing  the  loss  of  head  to  the 
lowest  possible  limit.  In  1898,  1 12,803  feet  of  mains  was  cleaned  a,t 
Halifax  at  an  average  cost  of  about  0.4  cent  per  foot.  For  some  of 
the  pipes  the  cost  was  as  low  as  o.  3  cent  per  foot.  * 

761.  Pumping-stations. — Where  a  water-supply  has  to  be  artificially 
elevated,  the  pumping-station  expenses  constitute  by  far  the  largest 
portion  of  the  operating  expenses  of  the  water-works  system.  It  is 
therefore  of  the  greatest  importance  that  the  highest  efficiency  be 
maintained  in  this  part  of  the  service.  This  can  be  secured  only 
through  skillful  attendance,  and  the  best  results  will  be  obtained  by 
paying  good  wages  to  good  men.  The  item  most  susceptible  of  varia- 
tion is  the  cost  of  coal,  and  every  effort  should  be  made  to  reduce  this 
to  the  lowest  practicable  limit.  A  daily  record  should  be  kept  of  the 
weight  of  coal  and  of  ashes,  so  that  the  efficiency  of  the  service  can  be 
known  at  all  times.  Frequently  a  premium  paid  for  low  coal  con- 
sumption is  of  much  aid  in  this  matter.  Sufficient  reserve  boiler  and 
pumping  capacity  must  be  provided  to  enable  repairs  to  be  made  and 
the  boiler  to  be  regularly  cleaned  and  overhauled.  Reserve  machinery 
should  be  operated  frequently  to  make  sure  it  is  in  good  condition  and 
can  be  started  when  called  for.  This  is  especially  important  where  it 
is  depended  upon  for  fire-pressure.  Careful  attention  must  be  given 
to  pump-valves  and  plunger-packing  in  order  to  keep  the  leakage  or 
slip  a  minimum.  Air  should  not  be  allowed  to  get  too  low  in  air- 
chambers  or  to  accumulate  too  much  in  vacuum-chambers.  Suction- 
pipes  should  be  kept  air-tight  and  a  free  entrance  provided  at  all  times 
*  See  further  data  in  Eng.  Record,  1904,  L.  p.  623. 


THE  DISTRIBUTING   SYSTEM.  781 

for  the  water.  The  motive  power,  whatever  it  may  be,  should  be 
maintained  at  a  high  efficiency,  and  should  have  the  same  careful 
attention  as  is  given  to  other  high-class  machinery. 

Records  should,  of  course,  be  kept  of  the  amount  of  water  pumped 
per  day,  and  the  pressure  maintained;  also  of  the  time  during  which 
special  fire-pressure  is  furnished,  and  the  amount  of  water  pumped  at 
this  pressure.  Recording  pressure-gauges  are  of  the  greatest  value  in 
maintaining  the  efficiency  of  a  plant.  By  the  use  of  several  such 
gauges,  placed  in  different  parts  of  the  city,  a  valuable  record  may  be 
obtained  of  the  actual  working-pressures  under  different  conditions. 
Such  records  will  be  of  especial  value  at  times  of  fires,  and,  if  the  pres- 
sure is  insufficient,  will  determine  whether  it  be  due  to  low  pressure  at 
the  pumps  or  to  inadequate  size  of  mains.  Recording-gauges  serve 
also  as  quick  detectors  of  pipe  breakages  and  the  occurrence  of 
stoppages,  so  that  means  can  be  at  once  taken  to  remedy  the  trouble. 
Probably  no  other  detail  of  equal  cost  is  of  such  great  value  to  the 
superintendent  as  is  a  reliable  recording-gauge. 

762.  Distributing-reservoirs,   Stand-pipes,  and  Tanks. — The  main- 
tenance of  earthen  reservoirs  calls  for  little  more  than  has  already  been 
mentioned  (page  337).      The  cleaning  of  such  reservoirs  may  need  to 
be  done  frequently.    It  is  usually  accomplished  by  flushing  out  the  mud 
through  the  waste-pipe   by  means   of  a  hose,    as  in   the  cleaning   of 
settling-basins.      Stand-pipes  and  tanks  may  require  occasional  flush- 
ing or  blowing  out,  and  will  need  to  be  repainted  at  intervals  of  a  few 
years.      They  should  also  be  inspected  for  signs  of  excessive  corrosion 
or  of  electrolysis,  and  for  any  indication  of  weakness  or  wear  at  the 
base.      Wooden  tanks  need  rigid  and  frequent  inspection  to  ascertain 
the  condition  of  the  wood  and  of  the  hoops.      One  or  two  of  the  latter 
will  probably  need  to  be  occasionally  removed  to  determine  this  point. 
Details  should  be  inspected  for  leaks.      Any  automatic  or  quick-acting 
valve  should  have  special  attention  to  make  certain  that  it  is  in  working 
condition. 

THE    DISTRIBUTING    SYSTEM. 

763.  In  the  operation  and   maintenance  of  a   distributing  system 
there   are   to   be    considered,    besides    the    questions    of  construction 
already  discussed,  the  cleaning  of  pipes,  detection  of  leaks,  repairs  of 
pipes,  prevention  of  corrosion,  provision  against  electrolysis,  thawing 
of  frozen  pipes,  care  of  valves  and  hydrants,  detection  and  prevention 
of  waste,  and  the  use  of  meters. 


72  OPERATION  AND    MAINTENANCE. 

764.  Mains  and  Service-pipes. — A  method  of  removal  of  incrusta- 
tion has  already  been  described  in  Art.   760.      To  remove  sediment 
from  the  pipe  system  use  is  made  of  blow-off  valves  or  hydrants.     Dead 
ends  may  need  quite  frequent  flushing  on  account  of  odors  and  bad 
tastes  developing  in  the  stagnant  water.      Large  leaks  in  mains  will 
quickly  make  themselves  known,    especially  if  a  recording  pressure- 
gauge  is  in   use.      Prompt  action  in   shutting  off  the   supply  is  often 
necessary  to  prevent  heavy  damage.      Small  leaks,  if  occurring  in  clay 
soil,  will  usually  be  indicated  by  the  appearance  of  water  at  the  surface, 
but  in  porous  soils,  and  especially  near  sewers  or  drains,  quite  large 
leaks  may  go  unnoticed  for  years.      These  may,  however,  be  detected 
by   the   method   described   in   Art.    768    for   the   detection   of  waste. 
Leaks  in  services,  between  the  curb-cock  and  the  house,  can  also  be 
likewise    detected.      Broken    sections    of  pipe    must   be   cut   out    and 
replaced,  either  by  cutting  the   pipe  and  putting  in  a  short  piece  by 
means  of  sleeve-joints,  or  by  melting  out  the  lead  joints  of  three  sec- 
tions and  introducing  a  new  length  of  pipe. 

765.  Electrolysis. — A  serious  form  of  corrosion   which   has  given 
trouble  in   many  cities  is  the  electrolysis  which  is  caused  by  return 
currents    from    single-trolley   electric    railways.      In    this    system    the 
return  current  is  supposed  to  pass  through  the  rails,  but  as  these  are 
not  insulated,  a  portion  passes  through  the  earth  to  neighboring  pipes 
or  other  conductors  leading  in  the  right  direction.      This  current  then 
flows  along  the   pipe  with   more  or  less  resistance  until  it  reaches  a 
neighborhood  where  the  rails   or  some  other  conductors  are  of  lower 
potential  than  the  pipe,  this  being  usually  in  the  vicinity  of  the  power- 
station.      The  current  then  leaves  the  pipe,  and  in  so  doing  sets  up 
corrosive  electrolytic  action.      Such  action  takes  place  only  where  the 
current  passes  from  the  pipe  to  the  ground,  and  not  where  the  current 
passes  from  the  ground  to  the  pipe.      It  depends  in  amount  upon  the 
strength  of  the  current,  and  upon  the  character  of  the  salts  in  the  soil. 
If  the  current  in  the  pipe  is  strong,  corrosion  will  also  take  place  near 
the  joints.      This  is  due  to  the  fact  that  the  joints  offer  relatively  high 
resistance,  thus  causing  a  part  of  the  current  to  leave  the  pipe  and  pass 
around  the  joint  through  the  soil  or  the  water  and  back  to  the  pipe  on 
the  other  side.      This  corrosion  near  the  joint  is  apt  to  be  much  less 
than  at  other  points,  but  recent  reports  indicate  that  it  is  likely  to  be 
serious. 

Electrolytic  corrosion  is  in  some  cases  so  rapid  that  pipes  are 
practically  eaten  through  in  three  to  four  years,  and  some  of  the  worst 
cases  have  occurred  where  the  pressure  is  but  \\  volts.  At  Peoria, 


THE  DISTRIBUTING   SYSTEM.  783 

111.,  a  stand-pipe  which  failed  had  been  badly  corroded  by  electrolysis, 
and  this  was  doubtless  a  prime  cause  of  its  failure. 

The  remedies  for  electrolysis  should  apparently  rest  entirely  with 
the  railway  companies.  The  double  trolley  is  the  only  complete 
remedy,  and  it  has  been  applied  extensively,  and  writh  success,  in  one 
or  two  places.  A  very  important  aid  in  preventing  electrolysis  is  the 
construction  of  a  good  return  conductor  by  means  of  good  rail-bonding 
and  the  use  of  adequate  return  wires.  Then  in  those  districts  where 
the  pipes  are  of  higher  potential  than  the  rails,  if  good,  low-resistance 
connections  are  made  between  rails  and  pipes,  or  from  pipes  to  special 
return  wires,  the  current  will  leave  the  pipes  without  passing  into  the 
ground  and  without  causing  trouble.  Voltmeter  tests  between  pipes 
and  rails,  at  various  points  over  the  city,  will  determine  the  danger  area, 
but  such  tests  should  be  made  under  a  variety  of  conditions  and  at 
occasional  intervals.  Pipes  and  rails  should  not  be  connected  outside 
of  the  danger  area,  as  this  only  aggravates  the  trouble  by  conducting 
more  current  into  the  pipes.  This  method  of  making  connections  to 
the  pipes  does  not  obviate  the  trouble  at  the  joints,  but  rather  in- 
creases it,  as  it  adds  to  the  conductivity  of  the  pipes. 

It  has  been  proposed  to  insulate  the  pipes  by  the  occasional  use  of 
a  wooden  section,  or  by  the  use  of  wooden  joints,  so  as  to  render  the 
pipe  a  poor  conductor.  The  success  of  such  means  would  depend  upon 
whether  the  current  could  be  sufficiently  reduced  to  avoid  electrolysis 
at  the  end  of  each  individual  section,  as  now  occurs  at  the  joints. 

766.  Thawing  Frozen  Pipes. — Not  infrequently  considerable  trouble 
arises  from  the  freezing  of  service-pipes  which  are  not  placed  at  a  suffi- 
cient depth.  Occasionally,  also,  small  mains  are  frozen.  Where  the 
proper  facilities  exist  the  best  way  to  thaw  frozen  pipes  is  by  warming 
them  with  an  electric  current,  a  method  applied  for  the  first  time  by 
Professors  Jackson  and  Wood  at  Madison,  Wis,  in  1898-99,  and 
which  has  been  used  in  many  places  since  then. 

For  thawing  service-pipes  a  current  of  200  to  300  amperes  at  a 
pressure  of  50  volts  is  satisfactory,  and  will  ordinarily  thaw  a  pipe  in 
from  20  to  30  minutes.  The  current. can  conveniently  be  taken  from 
electric-light  wires  and  reduced  by  a  transformer.  Connections  can 
readily  be  made  to  a  faucet  in  the  house  and  to  a  fire-hydrant  outside, 
or  to  faucets  in  two  houses.  To  regulate  the  current  large  sheet-iron 
terminals  can  be  immersed  in  a  bucket  of  salt  water.  Direct  connec- 
tion to  house-lines  should  not  be  made  on  account  of  the  danger  of 
fire.  A  6-inch  main  320  feet  long  has  been  thawed  in  two  hours  with 
a  current  of  350  amperes  at  100  volts. 


784  OPERATION  AND    MAINTENANCE. 

Where  the  electrical  method  cannot  be  used  steam  may  be 
employed,  not  only  to  warm  the  pipe,  but  to  excavate  through  the 
frozen  ground  in  a  way  similar  to  the  operation  of  the  water-jet.  The 
pipe  may  thus  be  reached  at  points  4  to  5  feet  apart  and  gradually 
thawed  out.  Service-pipes  are  often  thawed  by  the  use  of  a  small 
steam-pipe  inserted  in  the  service-pipe  through  the  house  end,  or  from 
an  opening  at  an  excavation  outside.  Ground  may  be  thawed  by 
maintaining  a  fire  on  the  surface  for  several  hours,  or  more  readily  by 
the  use  of  a  gas-flame  projected  against  the  soil. 

767.  Valves  and  Hydrants. — Valves  should  be  inspected  occasionally 
to  detect  leakage  and  to  ascertain  if  they  are  in  working  order  and  the 
boxes  clean.      Fire-hydrants  require  very  careful  attention,  'especially 
in  cold  climates,  as  it  is  of  the  greatest  importance  that  they  be  at  all 
times  available.     The  chief  trouble  with  fire-hydrants  is  from  the  freez- 
ing of  the  valves  due  to  imperfect  drainage,  although  a  hydrant  branch 
sometimes  freezes  up. 

Hydrants  should  be  carefully  examined  on  the  approach  of  cold 
weather  and  put  in  good  condition.  Valves  should  be  tight  and  the 
hydrant  thoroughly  drained.  If  so  located  that  the  hydrant  cannot  be 
drained,  it  should  be  pumped  out  each  time  after  being  used.  To 
ascertain  if  a  hydrant  is  drained,  a  lead  weight  tied  to  a  graduated  cord 
can  be  let  down  through  a  nozzle.  .  Hydrants  should  never  be  opened 
unnecessarily  in  cold  weather,  and  never  by  others  than  those  responsi- 
ble for  their  condition.  In  very  cold  climates  it  is  found  desirable  after 
using  a  hydrant  to  oil  the  packing  and  the  nut  at  the  top  with  kero- 
sene in  order  to  prevent  sticking  of  the  valve  and  nut. 

To  thaw  frozen  hydrants,  a  small  portable  steam-boiler  is  com- 
monly employed,  which  is  provided  with  a  length  of  hose  for  conduct- 
ing steam  to  the  bottom  of  the  hydrant.  Hot  water  may  also  be  used, 
and  for  mild  cases  a  little  salt  may  be  effective.  After  thawing,  the 
water  should  always  be  pumped  out. 

768.  Detection  and  Prevention  of  Waste. — From  the  data  given  in 
Chapter  II  it  was  made  evident  that  a  very  large  .percentage  of  the 
water  supplied  to  American  cities  is  wasted  by  the  consumer  and  lost 
by  leakage.      In  many  cities  the  consumption  of  water  is  easily  double 
the  amount  which  can  possibly  be  made  use  of,  and  in  a  very  large 
proportion  of  them  the  wastage  is  fully  one-third  of  the  entire  quantity 
supplied.      This  excessive  use  of  water  not  only  increases  the  cost  of 
pumping  unnecessarily,  but  adds  to  the  expense  in  all  parts  of  a  water- 
works system.     Its  effect  is  noticed  perhaps  most  of  all  in  the  reduction 
of  pressure,    since  the  frictional  head   is   nearly  proportional    to   the 


DETECTION  AND    PREVENTION  OF    WASTE.  785 

square  of  the  discharge.  For  the  same  reason  a  moderate  reduction 
of  the  consumption  will  result  in  a  large  increase  of  pressure.  The 
problem  of  waste-prevention  is  thus  seen  to  be  one  of  great  economic 
importance. 

Unquestionably  the  easiest  and  most  rational  method  of  prevent- 
ing the  waste  of  water  is  by  the  use  of  meters,  so  that  each  consumer 
will  pay  for  what  he  uses.  It  furnishes  also  the  most  equitable  basis 
for  charging  up  the  cost  of  service,  as  by  any  other  system  the  careful 
user  is  forced  to  pay  for  the  water  wasted  by  his  careless  neighbor. 
The  use  of  meters  is  becoming  much  more  general,  and  in  most  cities 
the  larger  consumers,  at  least,  are  now  metered ;  but  a  very  large  part 
of  the  loss  or  waste  is  due  to  the  small  consumer,  so  that  the  full 
benefit  of  the  system  will  not  be  felt  until  the  use  of  meters  becomes 
general.  Usually  much  opposition  is  raised  to  the  introduction  of 
meters,  but  after  they  have  been  put  into  use  the  results  are  commonly 
such  as  to  cause  them  to  be  greatly  favored  by  the  community.  The 
effect  of  the  use  of  meters  has  been  generally  discussed  in  Chapter  II, 
and  many  individual  cases  could  be  cited  showing  the  great  economy 
consequent  upon  the  introduction  of  the  meter  system.  As  a  system 
of  waste-prevention  it  is  always  in  service,  and  for  that  reason  is  far 
superior  to  any  system  of  inspection.  In  nearly  all  cases  the  decrease 
in  cost  of  supplying  water  after  the  adoption  of  meters  much  more  than 
balances  the  cost  of  the  meters. 

If  meters  are  not  used,  some  method  of  inspection  is  highly 
desirable  whereby  the  most  serious  cases  of  waste  can  be  detected  and 
the  consumption  kept  within  reasonable  limits.  The  most  common 
method  is  a  house-to-house  inspection,  carried  out  one  or  more  times 
per  year  for  the  purpose  of  examining  the  plumbing  fixtures.  Any 
leaky  or  imperfect  fixture  is  ordered  repaired,  and  the  premises 
reinspected  shortly  to  make  sure  that  the  order  has  been  complied 
with.  Persistent  refusal  is  followed  by  the  shutting  off  of  the  supply. 
This  method  of  inspection  cannot  be  carried  out  frequently,  and  is  of 
no  value  in  preventing  willful  waste  through  open  fixtures. 

A  comparatively  effective  method  of  house-to-house  inspection  was 
employed  temporarily  in  St.  Louis  to  avoid  a  water  scarcity.  A  night 
inspection  was  first  made  at  the  curb-cock  by  means  of  a  long  key  with 
the  end  flattened  so  that  the  ear  could  be  held  against  it.  By  turning 
the  water  off  and  then  turning  on  again,  a  flow  as  small  as  5  gallons 
per  hour  could  be  detected  by  the  hissing  noise  made.  Any  appreci- 
able flow  at  night  was  inquired  into  next  day,  the  house  fixtures 
inspected,  and  notice  given  to  avoid  the  waste  of  water.  The  same 


786  OPERATION  AND  MAINTENANCE. 

house  was  shortly  reinspected,  and  after  two  or  three  notices  to  repair 
plumbing  or  stop  waste  the  water  would  be  shut  off. 

If  meters  are  not  used  a  system  of  inspection  by  districts  will  serve 
to  determine  and  control  the  waste  to  a  considerable  extent.  To 
accomplish  this  some  method  of  measuring  the,  water  flowing  into  a 
given  district  must  be  employed.  This  system  of  district  inspection 
was  introduced  in  Liverpool  in  1873  by  Mr.  G.  F.  Deacon,  and  a  waste- 
water  meter  was  devised  by  him  to  determine  the  flow.*  His  meter 
is  in  general  use  in  many  cities  in  England  and  has  been  employed  to 
a  limited  extent  in  this  country.  A  more  convenient  and  economical 
method  of  determining  the  flow  for  inspection  purposes  is  by  -the  use  of 
the  Cole-Flad  pitometer.  This  instrument  consists  of  a  pair  of  Pitot 
tubes,  which  can  be  inserted  in  a  water  main  through  an  ordinary 
corporation  cock.  The  pressure  within  these  tubes  is  communicated 
to  a  glass  "  U  "  tube  and  recorded  photographically  by  suitable  appa- 
ratus. It  can  readily  be  carried  from  place  to  place  and  is  found  to  be 
very  satisfactory  for  inspection  purposes. •)• 

Jn  the  district  system  of  inspection  the  city  is  divided  into  sections 
of  a  few  blocks  each  and  valves  are  closed  controlling  the  section  so 
that  all  water  supplied  to  it  will  pass  the  meter  or  other  measuring 
apparatus.  If  the  records  thus  secured  show  the  night  consumption 
to  be  large,  thus  indicating  much  waste,  this  waste  is  then  localized  to 
certain  streets  as  far  as  possible,  by  shutting  off  different  streets  in 
succession  and  noting  the  resulting  curves.  Finally  the  houses  in  the 
worst  streets  are  inspected,  or  the  excessive  waste  localized  still  further 
by  closing  off  individual  services,  and  noting  the  effect  on  the  records, 
or  by  the  same  method  as  employed  at  St.  Louis. 

One  of  the  weak  points  of  the  meter  system  is  that  it  fails  to  detect 
leaks  in  the  mains  or  in  the  services  beyond  the  meters.  The  district 
system  is  advantageous  in  this  respect,  for  by  shutting  off  all  services 
the  leakage  in  the  mains  is  at  once  known.  It  may  thus  be  applied 
to  good  advantage  even  where  the  meter  system  is  in  operation,  if  a 
large  amount  of  water  is  "unaccounted  for."  To  localize  a  leak  in 
a  main,  a  waterphone  may  be  used,  which  consists  of  a  staff  of  wood 
or  iron  having  at  one  end  a  diaphragm  and  ear-piece  similar  to  a  tele- 
phone-receiver. The  staff  is  placed  against  the  pavement  over  the 
pipe  at  various  points,  and  the  ear  applied  to  the  receiver,  when  any 
sound  made  by  a  leak  is  readily  perceived. 

Any  method  of  waste-prevention  except  by  the  use  of  meters  is 
of  temporary  value  only  and  must  constantly  be  repeated,  and,  to  be 

*  See  illustration  in  Trans.  Am.  Soc.  C.  E.,  xxxiv.  p.  199. 
t  See  references  at  end  of  chapter. 


METERS.  787 

effective  at  all,  must  be  supported  by  strong  laws  and  good  plumbing 
ordinances. 

769.  Meters. — Water-meters  may  be  divided  into  two  general 
classes:  the  positive  displacement  meter,  in  which  a  definite  quantity 
of  water  passes  at  each  complete  movement  (neglecting  the  effect  of 
the  slight  clearance  necessary),  and  the  inferential  meter,  in  which  the 
moving  water  actuates  a  screw  or  other  similar  mechanism  and  the 
amount  of  flow  is  inferred  by  the  number  of  revolutions  of  the  screw. 
The  former  type  is  in  general  use  in  this  country;  but  the  latter  is  a 
common  form  abroad.  Both  forms  are  sufficiently  accurate  at  ordinary 
rates  of  flow,  but  the  inferential  type  is  the  less  accurate  at  low  rates. 
Of  the  displacement  meters  there  are  the  piston  type,  having  either  a 
reciprocating  or  a  rotary  piston,  and  the  disk  type,  in  which  a  disk  has 
a  sort  of  wobbling  motion  in  a  closed  chamber.  Most  of  the  meters 
in  use  are  of  the  rotary-piston  or  the  disk  type.  Many  different  kinds 
of  meters  are  on  the  market,  most  of  which  will  give  satisfactory 
service  if  properly  treated,  and  many  of  them  have  been  thoroughly 
tested  by  years  of  use.  No  new  form  of  meter  should  be  adopted 
without  thorough  and  long-continued  tests,  and  in  all  cases  it  is  well 
to  specify  the  desired  requirements  of  a  meter,  and  to  test  all  new 
meters,  in  order  to  insure  uniformly  good  workmanship. 

The  general  requirements  of  a  meter  are :  a  fair  degree  of  accu^ 
racy,  ability  to  register  approximately  quite  small  rates  of  flow,  suit- 
able capacity  for  a  given  loss  of  head,  durability,  and  low  cost.  All 
of  these  requirements  except  that  of  durability  can  readily  be  deter- 
mined by  a  brief  test.  Some  notion  of  the  durability  can  also  be  had 
by  a  careful  inspection  of  the  parts,  and  by  running  a  meter  at  a  rapid 
rate  for  a  considerable  period  and  again  determining  its  accuracy  and 
sensitiveness.  Maintained  accuracy,  accessibility,  and  ease  of  repairs 
are  the  most  important  qualities  of  a  meter. 

Great  accuracy  in  the  measurement  of  water  is  unnecessary.  Most 
meters  on  the  market  will  register  within  I  or  2  per  cent  of  the  correct 
amount  at  ordinary  rates  of  flow,  which  is  abundantly  accurate.  To 
avoid  dissatisfaction  it  is  desirable  that  the  error  of  registration  be  in 
favor  of  the  consumer.  A  small  error  is  otherwise  of  little  conse- 
quence. 

Sensitiveness,  or  accuracy  at  low  rates  of  flow,  is  much  more 
difficult  to  secure,  and  is  a  point  in  which  meters  differ  more  widely. 
Sensitiveness  is  desired  in  order  that  some  account  may  be  taken  of 
small  leaks,  which  in  the  aggregate  may  amount  to  a  large  proportion 
of  the  total  flow.  If  the  consumption  of  a  family  be  150  gallons  per 


788  OPERATION  AND   MAINTENANCE. 

day,  this  will  be  at  an  average  rate  of  about  6  gallons  per  hour.  A 
flow  of  water  at  a  uniform  rate  of  one-half  this  amount  would  not 
move  some  meters  at  all.  Great  accuracy  for  small  rates  is  not  needed, 
but  it  is  desirable  that  small  flows  be  accounted  for  in  part  at  least.  A 
sensitiveness  of  about  90  per  cent  registration  for  a  flow  of  10  gallons 
per  hour  ought  readily  to  be  obtained. 

In  a  test  of  fourteen  different  kinds  of  meters  by  J.  W.  Hill,* 
several  of  the  f-inch  meters  tested  would  register  a  flow  of  10  to  12 
gallons  per  hour  with  less  than  10  per  cent  of  error.  Tests  of  seven 
meters  by  J.  W.  Smith  t  gave  a  registration  of  95  per  cent  of  the  flow 
with  rates  of  3  to  24  gallons  per  hour.  His  experiments  also  showed 
little  reduction  of  accuracy  or  sensitiveness  in  the  best  meters,  after 
registering  an  amount  of  water  corresponding  to  thirty-five  to  forty 
years  of  service,  and  most  were  in  good  condition  after  a  use  corre- 
sponding to  one  hundred  years  of  service.  In  general,  the  disk  meters 
experimented  upon  showed  a  more  uniform  degree  of  accuracy  at 
different  rates  and  a  better  maintained  accuracy  than  the  piston  type. 
The  figures  just  mentioned  cannot  be  taken  as  indicating  the  actual  life 
of  a  meter,  as  many  other  things  besides  the  actual  wear  affect  the 
durability.  The  actual  life  of  a  good  meter  is  probably  not  over 
twenty  years,  and  in  many  cases  will  be  less  than  this.  The  accuracy 
and  durability  depend  much  on  whether  the  water  contains  suspended 
matter,  and  upon  the  character  of  the  same. 

Meters  should  be  so  designed  that  the  various  parts  will  be  easily 
accessible  and  readily  replaced,  and  the  moving  parts  protected  from 
serious  injury  by  frost.  The  latter  object  is  usually  accomplished  by 
frost-bottoms  of  cast  iron,  or  cast-iron  cases,  made  so  as  to  be  more 
easily  broken  than  other  and  more  costly  parts  of  the  meter. 

The  loss  of  head  in  a  meter  is  a  matter  of  some  importance,  as  this 
virtually  determines  the  size  necessary  for  a  given  capacity,  although 
meters  are  usually  rated  according  to  the  size  of  connecting  pipes. 
The  ordinary  sizes  for  domestic  service  are  f  and  £  inch.  The  loss  of 
head  in  seven  f-inch  meters  tested  by  J.  W.  Smith,  varied  from  3  to 
12  pounds  for  a  rate  of  flow  of  10  gallons  per  minute,  a  rate  which 
would  consume  about  70  feet  of  head  per  100  feet  off-inch  pipe.  For 
5  gallons  per  minute  the  loss  of  head  ranged  from  I  to  3  pounds. 
Mr.  Hill  found  in  disk  meters,  for  10  gallons  per  minute,  a  loss  of  6  to 
8  pounds,  and  in  piston  meters  7  to  13  pounds.  For  5  gallons  per 
minute  the  losses  were,  respectively,  2  to  2j,  and  2  to  3  pounds. 

*  Trans.  Am.  Soc.  C.  E.,  1899,  XLI.  p.  326. 
f  Ibid.,  p.  359- 


FINANCIAL. 

The  cost  of  I -inch  meters  is  ordinarily  from  $8  to  $12  each;  and 
cost  of  setting  $1.50  to  $3.00.  The  cost  of  maintenance  of  meters  at 
Providence,  R.  I.,  where  careful  accounts  have  been  kept,  is  as  follows: 
Interest  on  meters  and  setting,  50  cents;  depreciation,  assuming  a  life 
of  twenty  years,  75  cents;  maintenance  and  repairs,  testing,  etc.,  46 
cents;  reading  and  computing  bills,  42  cents;  total,  $2.13.  The  cost 
of  repairs  at  several  other  places  is  variously  reported  at  from  10  to  3  5 
cents  per  year. 

FINANCIAL. 

770.  General  Considerations. — The  financial  management  of  a  muni- 
cipal wrater-works  department  is  a  matter  of  much  importance  to  a 
community,  inasmuch  as  upon  this  management  depends  largely  the 
question  of  rates  and,  to  some  extent,  of  other  forms  of  taxation.     The 
total  cost  of  the  service  must  eventually  be  borne  by  the  community, 
but  much  care  is  necessary  in  fixing  the  rates  so  that  the  expense  will 
be  equitably  distributed,  both  with  respect  to  various  individuals  at  the 
present  time,  and  with  respect  to  future  generations.      To  fix  the  rates 
equitably  requires,  first,  a  careful  calculation  of  the  expenses  to  be  met ; 
then  a  determination  of  how  much  should  be  met  at  the  present  time 
and  what  portion  should  be  left  to  future  generations ;   then  what  pro- 
portion of  the  total  expense  should  be  raised  by  water  rates  and  what 
portion,  if  any,  by  general  taxation;  and  finally,  whether  it  be  wise  or 
expedient   to   so   adjust   the   rates   that  the  revenue  will   exceed   the 
expenditure  and  so  act  to  lower  taxation  in  other  ways.      In  the  case 
of  private  companies  the  last  element  would  represent  the  profit. 

In  many  respects  the  question  is  largely  a  matter  of  bookkeeping, 
but  it  is  highly  desirable  that  a  proper  and  businesslike  method  of 
accounting  be  adopted,  both  as  an  aid  in  equitably  fixing  the  charges, 
and  to  enable  the  public  to  know  the  exact  financial  condition  of  the 
water  department  as  a  separate  business. 

771.  Expenses  and  Charges  to  be  Met.— The  yearly  expenses  and 
charges  will  be  included  under  some  or  all  of  the  following  heads : 

1.  Interest  on  bonded  debt  incurred  for  construction. 

2.  Yearly  operating  and  maintenance  expenses. 

3.  Yearly  payment  into  a  sinking  fund  for  liquidating  the  bonded 
debt. 

4.  Yearly  payment   into  a   depreciation  fund    to    provide   for   the 
renewal  of  various  parts  of  the  works  when  worn    out  or   otherwise 
rendered  valueless. 


79°  OPERATION  AND    MAINTENANCE. 

5.  Yearly  cost  of  extensions  and  improvements. 

6.  Profit. 

Items  (i)  and  (2)  must  evidently  be  fully  met  year  by  year  by  the 
annual  income,  and  not  by  borrowing,  if  the  department  is  to  remain 
solvent.  The  only  question  is  as  to  what  should  be  included  under 
the  term  maintenance.  In  some  works  it  is  customary  to  charge  up 
some  part  of  the  cost  of  extensions  to  maintenance ;  also  the  replacing 
of  small  pipes  with  larger  ones,  and  renewals  of  various  other  portions 
of  a  plant.  But  to  keep  the  question  clear  it  is  usually  considered 
better  to  include  under  maintenance  only  the  regular  operating 
expenses  and  the  cost  of  minor  repairs. 

(3)  and  (4).  In  addition  to  the  interest  and  maintenance  expenses, 
a  fund  must  be  provided  from  the  annual  income,  either  for  the  pay- 
ment of  the  borrowed  money  by  the  time  the  works  are  worn  out, 
or  for  rebuilding  the  various  parts  when  necessary;  otherwise  a  city 
would,  in  the  course  of  time,  find  itself  with  a  worn-out  plant  on  its 
hands  and  a  bonded  debt  in  addition.  To  provide  both  a  sinking  fund 
and  a  depreciation  fund  would  be  to  tax  the  present  generation  for  the 
entire  first  cost  of  the  works,  and  for  its  renewal  or  its  maintenance  in 
perfect  condition.  This  method  of  management  is  usually  considered 
much  too  liberal  towards  the  future  generations,  but  may  be  adopted 
in  part  where  the  city  finances  are  in  good  condition. 

In  actual  practice  the  sinking  fund  usually  receives  the  most  and 
often  the  only  consideration,  and  by  some  States  such  a  fund  must  be 
provided  for.  If  the  sinking  fund  be  adjusted  to  pay  the  bonds  at  the 
end  of  a  period  corresponding  to  the  life  of  the  plant  as  a  whole,  or 
for  safety  a  little  short  of  this  time,  then  the  sinking-fund  provision  is 
equivalent  to  a  fund  for  depreciation,  and  the  finances  will  be  held  in 
equilibrium.  Renewals  will  then  be  paid  for  by  a  new  issue  of  bonds, 
and  the  payments  into  the  sinking  fund  will  continue.  To  provide  for 
contingencies  and  to  relieve  the  future  generations  to  some  extent,  it 
is  considered  good  policy  to  make  the  sinking  fund  such  as  to  pay  off 
in  time  all  the  original  debt,  including  that  portion  covering  the  per- 
manent parts  of  the  plant. 

If  a  sinking  fund  is  not  provided,  then  a  depreciation  fund  is  neces- 
sary. This  should  be  sufficient  to  furnish  funds  for  the  renewal  or  re- 
placement of  old  parts,  and,  as  a  margin  of  safety  in  calculating  the 
payments  into  this  fund,  the  more  permanent  portions  of  the  works 
should  be  assumed  to  have  a  limited  life.  A  portion  of  the  deprecia- 
tion fund  can  then  be  used  to  gradually  extinguish  a  part  of  the  bonded 
debt. 


FINANCIAL. 

(5)  The  cost  of  extensions  may  properly  be  met  in  the  same  way 
as  the  cost  of  new  works,  namely,  by  issuing  bonds  and  at  the  same 
time  providing  a  corresponding  increase  in  the  sinking  or  the  deprecia- 
tion fund.      Such  expenses  are,  however,  as  a  matter  of  accounting, 
often  paid  in  part  from  the  annual  receipts,  or  by  general  or  special 
taxation,  or  by  both  methods. 

(6)  As  a  general  proposition  there  can  be  no  ' '  profit ' '  derived  by 
a   city   from   supplying   itself  with  water.      If  more   is   paid   into   the 
treasury  than  sufficient  to  meet  the  expenses,  it  can  only  be  considered 
as  a  sort  of  indirect  tax  levied  for  other  purposes. 

From  these  considerations  it  is  evident  that  the  annual  charges 
upon  the  community  must  on  the  average  cover  at  least  the  in- 
terest on  the  bonded  debt,  the  operating  expenses,  including  ordi- 
nary repairs,  and  a  payment  into  a  sinking  or  a  depreciation  fund. 
(For  formulas  for  calculating  sinking  or  depreciation  funds  see  page 
2 1 6.) 

772.  Relative  Cost  of  the  Different  Services  Performed  by  a  Water- 
works.— The  functions  performed  by  a  water- works  are:   (i)  to  furnish 
water  for  private  use;   (2)  to  furnish  water  for  public  use  on  the  streets, 
and  for  sewers,  fountains,  public  buildings,  etc.  ;  and  (3)  to  furnish  fire 
protection  to  property.      In  (i)  and  (2)  the  cost  of  service  maybe  con- 
sidered approximately  proportional  to  the  quantity  of  water  supplied, 
but  in  (3)  it  is  out  of  all  proportion  to  the  amount  of  water  used,  for 
while  the   cost  of  construction  is   greatly  affected,   the  total   amount 
of  water  consumed  is  slight.      The  extra  cost  involved  in  furnishing 
adequate  fire  protection  is  due  to  largely  increased  pumping  capacity, 
increased  size  of  mains,   reservoirs,   or  stand-pipes,  cost  of  hydrants, 
and  increased  cost   of  maintenance.      Estimates   of  careful   observers 
place  the  proportion  of  interest,  depreciation,  and  maintenance  expenses 
chargeable  to  fire  protection  at  one-third  or  one-half  the  entire  cost. 
Another  very  considerable  part  of  the   expense  which  is  not  directly 
chargeable  to  present  consumers  of  water  is  the  provision  made  for 
future  growth.      The  expense  of  this  in  first  cost  may  also  easily  be 
one-third  the  entire  cost  of  construction. 

773.  Sources  of  Revenue. — The  sources   of  revenue  are  the  water 
rates  and  the  funds  received  by  general  taxation.     The  former  are  paid 
by  those  who  use  the  water,  and   more  or  less  in   proportion  to  the 
amount   used.      The    latter    are    paid   by   assessment   on   all    taxable 
property.      If  the  revenue  be  so   raised   that  each  interest  served  be 
charged  according  to  the  cost  of  the  service,  it  would  appear  from  the 


79 2  OPERATION  AND    MAINTENANCE. 

preceding  article  that  the  cost  of  furnishing  water  to  private  consumers 
should  be  paid  by  water  rates;  that  the  cost  of  supplying  water  for 
public  purposes  should  be  paid  by  taxation  and  according  to  the 
amount  of  water  used ;  and  that  the  cost  of  fire  protection  should  also 
be  met  by  taxation,  since  the  individual  is  benefited  by  reason  of  the 
protection  afforded  to  property.  The  expense  of  providing  for  the 
future  should  also  properly  be  met  by  the  city  as  a  whole,  and  there- 
fore by  general  taxation.  It  would  therefore  seem  that  ordinarily  from 
35  to  40  per  cent  of  the  total  expense,  plus  the  cost  of  the  water  used 
for  public  purposes,  should  be  met  by  general  taxation,  and  the 
remainder  of  the  revenue  obtained  from  the  water  rates.  The  exact 
proportion  of  the  revenue  which  should  be  derived  from  each  source 
depends  much  upon  local  conditions,  such  as  size  of  town,  character 
of  supply,  etc.  In  many  small  towns  the  works  are  primarily  installed 
for  fire-protection  purposes,  in  which  case  nearly  all  the  expense  should 
be  met  by  taxation.  It  is  also  good  policy  to  begin  with  fairly  low 
water  rates,  so  as  to  encourage  the  use  of  water,  but  to  enable  this  to 
be  done  a  large  proportion  of  the  expense  will  have  to  be  met  for  a 
few  years  by  taxation. 

In  most  water  departments  the  general  principle  of  distributing  the 
cost  as  above  outlined  is  recognized  by  making  payments  from  the 
general  fund  into  the  water  department,  either  yearly  or  at  irregular 
intervals.  In  but  few  places,  however,  is  the  system  fully  carried 
out. 

774.  Water  Rates. — The  proportion  of  the  revenue  to  be  derived 
from  private  consumers  requires  careful  consideration  in  its  adjustment. 
The  most  equitable  method  of  apportioning  the  cost  is  by  the  meter 
system.  In  fixing  rates  under  this  system,  allowance  should  be  made 
for  the  fact  that  quite  a  large  percentage  of  the  water  recorded  at  the 
pumping-station  cannot  be  accounted  for  (Chapter  II),  and  rates 
per  unit  of  volume  registered  by  the  meters  must  be  correspondingly 
raised. 

Meter  rates  are  usually  graduated,  that  is,  a  less  rate  is  charged  for 
large  quantities  than  for  small  ones.  This  is  partly  on  the  ground  that 
the  cost  of  meter  maintenance,  keeping  of  accounts,  etc*,  is  propor- 
tionally greater  for  small  quantities,  and  partly  by  reason  of  the  policy 
of  encouraging  the  operation  of  factories  which  contribute  largely  to 
the  general  prosperity  of  the  community,  and  which  may  require  large 
amounts  of  water.  In  establishing  a  graduated  schedule,  it  should  be 
so  made  that  the  lower  rate  shall  apply  only  to  the  additional  water 


LITER  A  TURE.  793 

used  beyond  the  limit  of  the  next  higher  rate.     An  example  of  such  a 
schedule  is  that  at  Madison,  Wis.,  which  reads  as  follows : 
For  1,500  cu.  ft.  or  less  per  6  months,  $2.00 
"  the  next  5,000  cu.  ft.    "    "       "          13  cts.  per  loocu.  ft. 
(i    (i        "i^  ooo  "     "    "    "       "         10   "      "      "     "     " 
"  all  over   21,500  "     "     "    "       "  5    "      "      "     "     " 

An  objection  to  the  meter  system  which  is  often  advanced  is  that 
it  discourages  the  use  of  sufficient  water  for  sanitary  purposes,  but  this 
is  entirely  obviated  by  making  a  small  minimum  charge,  such  as  given 
above,  which  will  be  enough  to  allow  the  use  of  an  abundance  of  water 
for  sanitary  purposes,  and  at  the  same  time  will  cover  the  expense  of 
meter  maintenance. 

Most  cities  meter  the  larger  consumers,  but  comparatively  few  have 
yet  introduced  the  full  meter  system.  In  such  cases  private  houses  are 
charged  mainly  by  the  fixture.  Usually  a  minimum  family  rate  is 
charged  for  kitchen  use,  then  an  additional  rate  for  each  bath-tub, 
water-closet,  wash-bowl,  stable-hose,  lawn-hose,  etc.,  with  often  other 
variations  depending  upon  the  number  of  rooms,  number  of  occupants 
of  the  house,  etc.  Little  data  exist  as  to  the  actual  amount  of  water 
used  by  different  fixtures,  and  the  rates  are  largely  arbitrary.* 

LITERATURE. 

GENERAL. 

1.  Jamieson.     The    Internal    Corrosion    of   Cast-iron    Pipes.      Proc.    Inst. 

C.  E.,  1880,  LXV.  p.  323.     Relates  to  the  use  of  scrapers. 

2.  Keating.     On  the  Removal  of  Incrustation  in  Water-mains.     Trans.  Am. 

Soc.  C.  E.,  1882,  xi.  p.  127.     Describes  work  done  at  Halifax. 

3.  A    Conduit-scrubbing    Machine.      Eng.    News,    1892,    xxvu.    p.    580. 

Machine  used  at  Boston. 

4.  Murdoch.     Cleaning  a  Water-main  at  St.  John,  N.  B.     Jour.  New  Eng. 

W.  W.  Assn.,   1899,  xin.  p.  333;  Eng.  News,  1899,    XLII.  p,  45. 
Use  of  scrapers  described. 

5.  Brackett.      Experiments    made   with   the    Deacon    Waste-water     Meter 

System.     Jour.  Assn.  Eng.  Soc.,  1882,  i.  p.  253. 

6.  Holman.     House-to-house   Inspection    to    Prevent   Water-waste.      Jour. 

Assn.  Eng.  Soc.,  1885,  iv.  p.  368. 

7.  Collins.     The  Prevention  and  Detection  of  Waste  of  Water.     Proc.  Inst. 

C.  E.,  1894,  cxvn.  p.  147.    Relates  to  the  use  of  the  waste-water  meter. 

8.  Water-waste  Prevention,  or  Increased  Pumping  Capacity.     Results  of  a 

thorough    investigation    of    consumption    and   waste    of   water   in 
American  cities,  by  H.  S.  Maddock.     Eng.  News,  1894,  xxxi.  p.  55. 

9.  Hague.     The  Value  of  Pressure-records  in  Connection  with  Water-works. 

Proc.  Am.  W.  W.  Assn.,  1891 ;   Eng.  Record,  1891,    xxm.  p.  345. 

*  For  rates  of  many  cities  see  Manual  of  Am.  W.  W.  Assn.,  1897,  pp.  i-xxxiv. 


794  OPERA  TION  AND  MAINTENANCE. 

10.  Bailey.     The  Care  of  Fire-hydrants  in  Winter.     Jour.  New  Eng.  W.  W. 

Assn.,  1899,  xiv.  p.  116;  Eng.  Record,  1899,  XL.  p.  387. 

11.  Cole.     Water-waste    and    Its    Detection.      Pitometer    described.      Jour. 

West.  Soc.  Engrs.,  1902,  vn.  p.  574. 

12.  Clemmitt.     Meter  System  of  the  Water  Department  of  Baltimore,  Md. 

Eng.  News,  1902,  XLVIII.  p.  355. 

13.  Patch.     Measurement  of  the  Flow  of  Water  in  the  Sudbury  and  Cochitu- 

ate  Aqueducts.     Eng.  News,  1902,  XLVII.  p.  488. 

14.  The  Loss  of    Capacity  of  the  Vyrnwy  Aqueduct.     Eng.  Record,   1902, 

XLVI.  p.  103. 

15.  Ericson.     Report  on  Water-waste  and  the  Metering  of  the  Water-supply 

of  Chicago.     Eng.  News,  1903,  XLIX.  p.  41. 

1 6.  Bemis.     Methods   and   Cost   of  Installing  Meters   at   Cleveland,  Ohio. 

Eng.  News,  1903,  L.  p.  373. 

17.  Investigations    of    Water-waste    in    New    York    City.       Pitometer  used. 

Department  Report  of  N.  S.  Hill.     Abstracts  in  Eng.  News,  1903, 
XL.  p.  135  ;  Eng.  Record,  1903,  XLVII.  pp,  122,  404,  XLVIII.  p.  340. 

18.  Thawing  Water-pipes  by  Electricity.     Eng.  News,  1904,  LI.  p.  251. 

19.  Ritchie.     Scraping    Water-mains    at   Melbourne.     Paper    before    Inst. 

C.  E.     Abstract,  Eng.  Record,  1904,  L.  p.  623. 

20.  Brown.     Incrustations,  Deposits,  and    Organic    Growths    in    Pipes   and 

Conduits.     Paper  before  Inst.  C.  E.     Abstract,  Eng.  News,   1904, 
LII.  p.  253. 

21.  Fuertes.     Report  on  Water-waste  in  New  York  and  Its  Reduction  by 

Meters  and  Inspection.     Abstract,  Eng.  News,  1906,  LVI.  p.  150. 

22.  Cole.     Pitometers.     Proc.  Am.  W.  W.  Assn.,  1907. 

23.  Hill.     Tuberculation  and  the  Flow  of  Water  in  Pipes.     Proc.  Am.  W.  W. 

Assn.,  1907. 

ELECTROLYSIS. 

1.  Jackson.     The  Corrosion  of  Iron  Pipes  by  the  Action  of  Electric  Railway 

Currents.     Jour.  Assn.  Eng.  Soc.,  1894,  xm.  p.  509. 

2.  Farnham.     Electrolysis  of  Water  and  other  Subterranean  Pipes  by  Elec- 

tric Currents.     Trans.  Am.  Inst.  E.  E.,  April,   1894;    Elec.  Eng., 
April  25,  1894. 

3.  Barrett.     Report  to  Commissioners  of  Electric  Subways  of  Brooklyn  on 

the    Subject   of   Electrolysis.      Abstract,  Eng.  Record,   1895,  xxxi. 
p.  225. 

4.  Electrolysis  of  Water-pipes  at  Dayton,  Ohio.     Report  of  investigation. 

Abstract,  Eng.  News,  1898,  XL.  p.  218. 

5.  Electrolysis  at  Kansas  City.     Report  of  Prof.  L.  I.  Blake  in  regard  to. 

Eng.  Record,  1899,  XL.  p.  239. 

6.  Maury.     Electrolysis  of  Underground  Metal  Structures.      Corrosion  of 

the  Peoria  Stand-pipe  and  Water-mains.     Proc.  Am.  W.  W.  Assn., 
1900;  Eng.  News,  1900,  XLIV.  p.  38. 

7.  Knudson.     Cause  and  Effect  of  Electrolytic  Action  upon  Underground 

Piping   Systems.     Jour.  New  Eng.  W.  W.  Assn.,  March,  1901;  Eng. 
Record,  1901,  XLIII.  p.  322. 

8.  Stearns.       Electrolysis  on   the    Metropolitan    Water-works.     Report   on. 

Abstract,  Eng.  Record,  1905,  LII.  p.  120. 


LITERATURE.  795 

METERS. 

1.  Rice.     The  Methods  and  Apparatus  used  in  the  Recent  Test  of  Water- 

meters  at  Boston.     Jour.  Assn.  Eng.  Soc.  1888,  vil.  p.  285. 

2.  Thompson.      A    Memoir   on    Water-meters.       Trans.    Am.   Soc.  C.  E., 

1891,  xxv.  p.  40. 

3.  Gill.     The  Sale  of  Water  by  Meter  in  Berlin.     Proc,  Inst.  C.  E.,  1892, 

cvn.  p.  203. 

4.  Thompson.     Uniformity  of  Methods    in    Testing  Water-meters.       Jour. 

New  Eng.  W.  W.  Assn.,  1895,  x.  p.  77. 

5.  Bericht  der  Commission  fiir  Wassermesser-Normalien.     Jour.  f.  Gasbel. 

u.  Wasservers.,  1896,  xxxix.  p.  699.  Results  of  tests  on  a  large 
number  of  meters,  and  suggested  standards. 

6.  Meter-testing  Apparatus,  Somerville,  Mass.     Eng.  Record,  1898,  xxxvm. 

p.  402. 

7.  Hill.     The  Accuracy  and  Durability  of  Water-meters.     Trans.  Am.  Soc. 

C.  E.,  1899,  XLI.  p.  326. 

8.  Nuebling.      A   Meter-testing   Apparatus   used   at    Reading,   Pa.     Eng. 

Record,  1899,  XL.  p.  698. 

9.  Burdick.     Accuracy  Tests  of   Water-meters   at  Des  Moines,   la.     Eng. 

News,  1905,  LIII.  p.  266. 

FINANCIAL. 

1.  Tubbs.     Particulars    in   which    Municipal    Officers    should    Protect   the 

Municipal  Corporations  in  Granting  Water-works  Franchises  to 
Private  Companies.  Proc.  Am.  W.  W.  Assn.,  1892  ;  Eng.  News, 
1892,  xxvn.  p.  518. 

2.  The  Regulation  of  Private  Water-rates.     Eng.  News,  1892,  xxvn.  p.  201. 

3.  Coffin.     The  Financial  Management  of  Water-works.     Jour.  New  Eng. 

W.  W.  Assn.,  1896,  xi.  p.  63. 

4.  Kiersted.     Valuation  of  Water-works  Property.     Trans.  Am.  Soc.  C.  E., 

1897,  xxxvni.  p.  115.     Extensive  discussion. 

5.  Kuichling.     The  Financial  Management  of  Water-works.     Trans.  Am. 

Soc.  C.  E.,  1897,  xxxvm,  p.  i. 

6.  Manual  of  American  Water-works,   1897.     Contains    much   information 

on  the  questions  of  ownership  and  of  water-rates. 

7.  Hermann.     Water-rates.     Elaborate  paper   before   the  Am.   Soc.  Muni- 

cipal Improvement.     Eng.  Record,  1899,  XL.  p.  459. 

8.  Hill.     Valuation  Clauses*  in  Water-works  Franchises.     Proc.  Am.  W.  W. 

Assn.,  1899,  p.  233;  Eng.  Record,  1899,  xxxix.  p.  594. 

9.  Sawyer.     Hydrant  Rental.     Municip.  Eng.,  March,  1903. 

10.  Tighe.     Municipal    Water-supply    Revenue.     Jour.    New    Eng.    W.    W. 

Assn.,  December,  1904. 

11.  Regulations  of   the  Engineering    Bureau,  Board  of  Water-supply,  New 

York.     Eng.  Record,  1906,  LIV.  p.  357. 


INDEX. 


Aeration: 

effect  of,  on  bacteria,  163. 
efficiency,  535. 
in  removal  of  iron,  541. 
methods  of,  534. 
Air-chambers  for  pumps,  666,  735. 

for  wells,  305. 
lift  pump,  662. 
valves,  614. 
Algae,  development  in  reservoirs,  178. 

odors  due  to,  167. 
Amoeba  coli,  198. 
Ammonia,  albuminoid,  128. 

free,  128. 
Anabcena,  168. 
Anaerobic  cultures,  136. 
t   Analysis  of  water,  sanitary,  118. 
Analytical  methods,  different,  120. 

value  of,  120. 
samples,  collection  of,  116. 
bacterial,  117. 
chemical,  117. 
Anchor-ice,  269. 
Anderson  process,  543. 
Animal  tests  in  water  analysis,  137. 
Annuities,  table  of,  218. 
Anthrax,  vitality  of,  in  water,  202. 

fever,  197. 

Aqueduct  bridges,  see  Bridges. 
Aqueducts,  ancient,  2. 
cleaning,  778. 
maintenance,  778. 
masonry,  see  Masonry  aqueducts. 
Roman,  2. 
Zempola,  8. 
See  also  Conduits. 
•  Artesian  strata,  capacity  of,  108. 
Dakota  sandstone,  in. 
occurrence    along    the    Atlantic    Coast, 

no. 

occurrence  in  the  United  States,  no. 
Potsdam  sandstone,  109,  112. 
value  of,  1 08. 
water,     bacterial     content     of,     at     Du- 

buque,  176. 
denned,  107. 

wells,  arrangement  of,  314. 
boring  of,  309. 
in  rock,  310. 

in  soft  materials,  309,  310. 
casing,  312. 

conditions  requisite,  106. 
cost,  313. 


Artesian  wells,  Dakota,  289. 

examples,  289,  313. 

failure  of,  317. 

flow  of  water  into,  283,  285. 

location,  no. 

operation,  315. 

predictions  concerning,  no. 

Rockford,  316. 

size,  313. 

spacing,  313. 

yield,  317. 
Asphalt  for  reservoir  lining,  700. 

for  pipe  coating,  569. 
Asterionella,  167,  168,  178. 
Atmosphere,  pressure  of,  224. 

Bacillus  cloaca,  138. 
coli  communis,   as  index  of  fecal   polli* 

tion,  138. 

methods  of  isolation,  139. 
enteritidis  sporogenes,  137,  138. 
lactis  aero  genes,  138.    ' 
typhosus,  methods  of  isolation,  141. 

relation  of,  to  colon  organism,  139. 
Bacteria,  effect  of  sunlight  on,  161. 
growth  of,  in  spring- waters,  172. 
in  ice,  168. 
in  soil,  152. 

multiplication  of,  in  water  samples,  133. 
organic  nutriment  on  growth  of,  176. 
significance  of  liquefying,  135. 
vitality  of  disease,  199. 
Bacterial  analysis  of  waters,  120,  121. 

quantitative,  132. 
content  of  Isar  River,  156. 
Lake  Superior,  164. 
Potomac  River,  156. 
rain-water,  153. 
spring-water,  172. 
streams,  156. 
wells,  174,  176. 
purification  of  rivers,  157. 
Danube,  157. 
Hudson,  158. 
Illinois,  159. 
Isar,  158. 
Rhine,  157. 
tests  of  filters,  491. 

scope  of,  131. 
Backfilling,  773. 
Balanced  valves,  616. 
Bell-and-spigot  joint,  557. 
Belting,  efficiency  of,  644. 


797 


INDEX. 


Berkefeld  filter,  532. 

Blood-heat,  effect  of,  on  bacterial  growth, 

133- 

Blow-off  valves,  615. 
Boiler-scale,  151,  419,  537. 
Bridge,  aqueduct,  3,  5,  598. 
for  pipe-lines,  573,  618. 

Canals,  cost  of,  624. 
cross-sections,  590. 
details,  591. 
flow  of  water  in,  589. 
gates,  592. 
slopes,  589. 
use  of,  589. 
.velocities  in,  589. 
Carbolic  acid  and  sulphuric  acid,  effect  of 

mixing,  142. 

Cast  iron,  strength  of,  555,  651. 
Cast-iron  pipe: 
branches,  560. 

calculations  of,  238,  242,  760,  768. 
coating,  563. 
-    corrosion,  564,  782. 
cost,  604,  625,  626. 
covering,  610,  772. 
derrick  for,  608. 
distortion  of,  554. 
durability,  564. 
economical  size,  603. 
flow  of  water  in,  238. 
inspection  of,  563. 
intakes,  623. 
joints,  557. 

bell-anti-spigot,  557. 

flanged,  560. 

flexible,  621,  623. 

rubber,  560. 

sleeve,  560. 

special,  623. 

standard,  558,  559, 

turned,  559. 
laying,  607. 
manufacture,  561. 
material  for,  561. 
specials,  560. 
Standard  weights,  557. 
stresses  in,  551. 
testing,  564. 
thickness,  555. 
tuberculation,  564. 
use  of,  555. 
weight  of,  555,  564. 
Cement  pipe,  581. 
Centrifugal  pumps,  316,  661,  670. 
Check-valves,  616. 

Chemical  analysis  of  water,  120,  125. 
data,  expression  of,  125. 

interpretation  of,  126. 
reaction  of  water,  125. 
Chemicals,   use  of,   in   detecting  pollution, 

119. 

in  water  purification,  544. 
Chlorinated  lime  in  water  purification,  545. 


Chlorine,   increase   of,   in   inhabited   areas, 

128. 

relation  of,  to  quality,  127. 
Cholera,  184. 
infantum,  197. 
organism,  isolation  of,  137,  141. 

vitality  of,  in  waters,  202. 
outbreaks: 

epidemics  in  the  United  States,  195. 
Hamburg,  196. 
London,  195. 

Circulation,  vertical,  of  lake  waters,  165. 
Cities,  growth  of,  34. 
Clark  process,  538. 
Clear-water  reservoir  for  filters,  487. 

for  settling-basins,  444. 
Closterium,  168. 

Coagulants,  action  of  various,  432,  506. 
amount  required,  434. 
efficiency  of,  437. 
iron,  432. 

sulphate  of  alumina,  432. 
use  of,  in  filtration,  494,  506,  526. 

in  sedimentation,  431. 

Colon   bacillus,   relation  of,  to  typhoid  or- 
ganism, 137. 
significance  of,  135. 
Color  of  water,  122. 

Comparison   of  waters   by  qualitative   bac- 
terial analyses,  134. 
by  quantitative  bacterial  analyses,  133. 
Concentration    of    bacteria    in    water    an- 
alysis, 138. 

Condensers,  value  of,  640. 
Conduits,  canal,  see  Canals, 
capacity,  587. 

cast-iron,  see  Cast-iron  pipe, 
classes  of,  586. 
location,  587. 
maintenance,  778. 
masonry,  see  Masonry  aqueducts, 
pipe,  see  Pipe-lines, 
single  vs.  double,  587. 
steel,  see  Pipe-lines. 
Consumption  of  water,  by  ancients,  8. 
effect  of  meters  on,  18,  25. 
fire  rate,  20,  31,  745. 
for  commercial  purposes,  18. 
domestic  purposes,  17. 
public  purposes,  19. 
street-sprinkling,  20. 
in  American  cities,  23. 
in  European  cities,  33. 
increase  in,  17,  24. 
influences  affecting,  16. 
loss  and  waste,  20,  784. 
maximum  rate,  32,  745,  751. 
total,  per  capita,  22. 
variations  in,  26. 
daily,  27. 
hourly,  29. 
monthly,  26. 
waste,  20,  784. 
Copper  sulfate  in  water  purification,  546, 


INDEX. 


799 


Core-walls,  345,  348. 

masonry,  349. 

position  of,  351. 

puddle,  348. 

steel,  351. 

wooden,  351,  357. 
Corrosion  of  pipes,  564,  570,  782. 
Coupling-shoes  for  stave-pipe,  579. 
Covered  reservoirs,  704. 

data  on,  706. 

masonry,  705. 

wooden,  705. 
Crenothrix,  170,  179. 
Croton  aqueduct,  coefficients  for,  258. 

sections  of,  596. 
Crops,  use  of  water  by,  61. 
Culverts  for  aqueducts,  598. 

Dakota  sandstone,  in. 
Dams,  considered  as  porous,  339. 
buttress  type,  407. 
reinforced  concrete,  407. 
earthen,  343. 

advantages,  of,  343. 

clay  in,  347. 

conditions  requisite  for,  343. 

construction,  354. 

floods  during,  370. 

foundation,  354. 

hydraulic,  355. 
core-walls,  345,  348. 

masonry,  349. 

position  of,  351. 

puddle,  348. 

steel,  351. 

wooden,  351,  357. 
cost,  371. 
culverts  in,  359. 
faces,  357. 
forms  of,  344. 
foundations,  344,  353,  356. 
gate-chambers,  361,  367. 

screens,  365. 

sluice-gates,  366. 
height  of,  352. 
hydraulic  construction,  355. 
material  for,  347. 
outlet  pipes  and  valves,  357,  366. 
percolation  in,  341. 
pipes  in,  358. 
porous,  356. 
puddle  for,  348. 
slopes,  352,  356. 
stability,  345. 
top  width,  353. 
tunnels  in,  359. 
wasteways  for,  369. 
kinds  of,  339. 
loose  rock,  414. 
maintenance,  337. 
masonry,  374. 
advantages,  374. 
conditions  requisite,  374. 
construction,  392,  394. 


Dams,  masonry,  cost,  409. 
curved,  388. 
action  of,  388. 
examples,  390. 
draw-off  arrangements,  397. 
errors  in  theory,  376,  384. 
earth  backing  for,  396. 
examples,  404. 
forces  acting,  374,  387. 
foundation,  392. 
earth,  393. 
water  in,  394. 
gate-chambers,  399. 
height  above  water,  388. 
high,  381. 

examples,  405. 
ice  action  on,  387. 
imperviousness,  396. 
internal  pressure  in,  387. 
leakage,  396. 
low,  379. 

examples,  404. 
outlet-pipes,  397. 
pressures  allowable,  379. 
profiles,  385,  386. 
stability,  377. 

high  dams,  381,  387. 
low  dams,  379. 
standard  profile,  385. 
stresses  in,  375. 
top  width,  388. 
triangular  profile,  386. 
valves  for,  399. 
water-pressure  in,  387. 
waste-weirs,  forms  of,  400. 
examples,  401,  402,  403. 
wave-action  on,  387. 
Wegmann's  formulas,  382. 
weight  of,  379. 
wind-pressure  on,  387. 
porosity  of,  339. 
pressure  of  water  in,  339,  387. 
reinforced  concrete,  407. 
requisites  of,  339. 
rock-fill,  414. 
steel,  415,  417. 
timber,  412. 
Darcy's  formula,  240. 
Data  necessary  in  water  examination,  115. 
Deacon  waste-water  meter  system,  784. 
Death-rates    from    typhoid,    large    cities    in 

the  U.  S.,  186. 
Massachusetts,  186. 
Deep-well  pumps,  316,  660,  668. 
Deep  wells,  see  Artesian  wells. 
Depreciation,  calculation  of,  217,  218. 
of  works,  220. 
fund  for,  790. 

Derrick  for  pipe-laying,  608.  [160. 

Dilution,  effect  of,  on  purification  of  streams, 
Direct  pumping  system,  209. 
Disease  bacteria,  in  lake-mud,  166. 

vitality  of,  in  water,  197. 
disseminated  by  water,  183. 


8oo 


INDEX. 


Disinfection  of  wells  and  pipes,  141. 

Distillation,  543. 

Distributing  pipes,  arrangement  of,  748,  762. 

calculation,  760,  768. 

covering,  772. 

flow  through  compound  pipes,  758. 

location,  770. 

loss  of  head  in,  242,  756. 

maintenance,  778. 

relative  capacity,  758. 

thawing,  783. 
reservoirs,  automatic  valve  for,  719. 

capacity,  690. 

construction,  696. 

cost,  719. 

covered,  704,  707. 

depth,  697. 

elevation,  694. 

form,  694. 

gate-chambers,  703. 

high-water  alarm,  720. 

kinds  of,  352. 

linings,  697,  700. 

location,  693. 

masonry,  702. 

maintenance,  781. 

outlet  pipes,  703. 

purpose  of,  689. 

reinforced  concrete,  699,  702,  707. 

value  of,  689,  693. 

valves  for,  703. 
system,  742. 

ancient,  7. 

arrangement,  748,  762. 

calculation,  758,  760. 

cost,  625. 

examples,  750,  765. 

fire-pressure  required,  745. 

fire-streams  required,  745. 

hydrant  location,  747. 

maps  of,  765. 

pressure  required,  743,  769. 

records,  775. 

requirements,  742,  751. 

services,  772. 

valves,  770. 

velocities  in,  752. 

zones  of  pressure,  769. 
Distribution,    effect     of,    on     quality,    177, 

179. 

Domestic  filters,  532. 
Driven  wells,  see  Wells,  tubular. 
Dug  vs.  driven  wells,  pollution  of,  141. 
Dysentery,  198. 

Earth,  pressure  of,  on  pipes,  553. 
Earthen  dams,  see  Dams,  earthen. 
Efficiency  of  generators  and  motors,  637. 
Electrical  purification  processes,  542= 

transmission,  649. 
Electrolysis,  782. 
Elevated  tanks,  see  Tanks. 
Embankments,  construction  of,  354,  696. 

for  aqueducts,  597. 


Energy,  equivalent  units  of,  634. 
generation  of,  637. 
losses,  635,  674. 
sources  of,  635. 
transmission  of,  644. 
Enrichment  cultures,  137. 
Evaporation,  54. 

from  land-surfaces,  57. 

determined  from  stream-flow,  63. 
effect  of  vegetation,  61. 
experiments  on,  62,  64. 
formula  for,  63. 
from  water-surfaces,  55. 
at  Boston,  55. 
Lee  Bridge,  57. 
Rochester,  56. 

calculated,  for  U.  S.,  57,  58. 
experiments  on,  55,  56. 
relation  to  stream-flow,  54. 
Examination  of  water-supplies,  115. 
Expansion-joints,  610. 

Fecal  bacteria,  character  of,  136. 
Fermentation-tube,  use  of,  135. 
Filter,  Fischer  system,  530. 
control,  bacterial,  142,  491. 
cribs,  322. 
galleries,  284,  318. 
Filters,  domestic,  532. 

mechanical,  see  Filters,  rapid  sand, 
rapid  sand: 

action  of,  506. 

advantages  of,  512. 

agitating  system,  523. 

arrangement  of,  513,  526. 

Chester,  Pa.,  504. 

Cincinnati,  515,  519. 

collecting  pipes,  520. 

Columbus,  518. 

coagulating  system,  526. 

cost,  528. 

description  of,  502. 

details  of,  515. 

experiments  on,  507. 

head  on,  525. 

history  of,  502. 

Little  Falls,  N.  Y.,  505,  511. 

Maignen  "scrubber,"  530. 

operation  of,  527. 

preliminary  filters,  494,  530. 

rate  for,  525. 

sand  bed,  515. 

strainer  system,  520. 

types  of,  503. 

use  of,  422,  503. 

wash  water  system,  524. 

Watertown,  N.  Y.,  513,  515. 

Youngstown,  O.,  513,  527. 
slow  sand: 

acreage  of,  451. 

Albany,  465,  467,  477. 

arrangement,  451,  466,  487. 

beds,  size  and  number,  464. 

bacterial  control  of  operation,  491. 


INDEX. 


801 


Filters,  slow  sand:  capacity,  45i»  464- 
cleaning,  487. 
clear-water  reservoir,  487. 
construction,  451,  466,  475. 
cost.  496 
covers,  469. 
depth  of,  468. 

of  water  on,  475. 
drainage  systems,  475. 
loss  of  head  in,  478,  479. 
effluent,  bacteria  in,  457. 
friction  in,  473,  480. 

drains,  478. 

gravel,  479. 

sand,  473. 

gravel,  loss  of  head  in,  479. 
inlet  pipe,  481. 
interior  of,  468. 
intermittent,  496. 
loss  of  head  in,  473,  478,  480. 
operation,  491. 

cost  of,  497. 
outlet  pipes,  481. 
period  of  service,  488. 
Philadelphia,  478. 
preliminary,  494,  530. 
pipes  for,  481,  486. 
pure-water  reservoir,  487. 
regulators,  481. 

automatic,  484. 
sand  for,  471. 

analysis,  471. 

selection,  472. 

washing,  490. 
sand  bed,  friction  in,  473. 

thickness,  474. 
sand  washers,  490. 
sediment  layer,  455. 
scraping,  487. 
use  of,  in  U.  S.,  451. 
valves  regulating,  481,  484,  486. 
washing  of  sand,  490. 
Zurich,  478. 
types  of,  451. 

Filtration,  extent  of,  in  soil  to  effect  puri- 
fication, 171. 
history,  10,  450. 

mechanical,  see  Filtration,  rapid  sand, 
rapid  sand: 

coagulation  and,  506. 
cost  of,  527. 
efficiency  of,  507,  512. 

Brooklyn,  N.  Y.,  511. 

Little  Falls,  N.  J.,  511. 

Moline,  111.,  511. 
experiments  on,  507. 

Cincinnati,  508. 

Louisville,  507. 

New  Orleans,  510. 

Pittsburgh,  509. 

Washington,  509. 
rate  of,  525. 
sedimentation  and,  506. 
theory  of,  506. 


Filtration,  slow  sand: 

bacteria  in  effluent,  457. 
bacterial  control,  491. 
biological  action,  454. 
chemical  action,"  453. 
coagulation  and,  494. 
double,  495. 
efficiency,  452,  458. 
bacterial,  452,  458. 
chemical,  453.     - 
death-rates  as  measure  of,  460. 
effect  of  cold,  470. 
rate,  462. 
scraping,  489. 
effluent,  bacteria  in,  457. 
history  of,  450. 
intermittent,  496. 
mechanical  action,  453. 
rate  of,  451,  461. 

regulation  of,  481. 
results  of,  452,  460. 
sedimentation  and,  493. 
theory,  452,  453. 
through  river-bed,  318. 
Financial  management,  789. 
Fire-boats,  773. 
Fire-cisterns,  747. 
Fire-pressures,  743. 
Fire-streams,  hydraulics  of,  250. 

number  required,  746. 
Fire-supply,  cost  of,  791. 

separate,  213,  773. 
Fires,  consumption  of  water  for,  31. 
Fish -screens,  365. 
Fishy  odors,  167. 
Flexible  joints,  621,  622,  623. 
Floods,  estimating,  74. 

examples,  77. 
Flow  of  streams,  66. 

annual  and  seasonal,  78. 
estimates,  83,  85. 
minimum,  80. 
statistics  of,  79. 

distribution  of,  through  the  year,  86. 
effect  of  lakes  and  ponds,  85. 
maximum,  69. 

diagrams  for,  75,  76. 
estimates   74. 
examples  of  floods,  77. 
formulas,  72. 
statistics,  70. 

methods  of  estimating,  66. 
minimum,  68. 
monthly,  82. 
units  of  measure,  67. 
Flow  of  water  in  filter-drains,  478,  479. 
in  hose,  251. 
in  hydrants,  252. 
in  open  channels,  256. 
coefficients,  257,  600. 
formulas,  256. 
Kutter's  formula,  256. 
coefficients  for,  257. 
measurement  of,  258. 


802 


INDEX. 


Flow  of  water  in  tunnels,  600. 
in  pipes,  235. 

coefficients  for  cast-iron  pipe,  238. 

compound  pipes,  758. 

Darcy's  formula,  240. 

diagram  for  cast-iron  pipe,  242. 

distributing  pipes,  242,  756. 

fire-hose,  250. 

Flamant's  formula,  240. 

formulas,  237,  241. 

friction  of  water,  nature  of,  2*37. 

general  relations,  235. 

Lampe's  formula,  240. 

loss  of  head  at  entrance,  249. 
due  to  bends,  249. 
contraction,  249. 
enlargement,  249. 

in  valves,  249. 

measurement  of,  248. 

old  pipe,  242. 

riveted  pipe,  245. 

service-pipes,  244. 

smooth  pipe,  245. 

wooden  pipe,  247. 
over  weirs,  228. 

sharp-crested,  228. 

submerged,  231. 

various  forms,  231. 
through  niters,  473,  478. 

gravel,  99,  479. 

nozzles,  251. 

orifices,  226. 

rock  strata,  109 

sand,  96,  473. 
Flowing  waters,  154. 

physical  appearance,  155. 
Flumes,  592. 

Fluorescein,     use    of    in     detecting    pollu- 
tion, 119. 

Food-supply,    lack   of,   on    bacterial   purifi- 
cation of  streams,  162. 
Fountains,  water  for,  20. 
Frazil  ice,  269. 
Friction,  fluid,  237. 
Frontinus,  7. 
Fuels,  calorific  value  of,  637. 

Galleries,  see  Filter  galleries. 
Galvanized  iron  pipe,  582. 
Gas-engines,  efficiency  of,  643. 
G astro-intestinal  diseases,  198. 
Gate-chambers,  361,  367,  399. 
Gates,  aqueduct,  599. 

canal,  592. 
Gatun  dam,  357. 
Gearing,  efficiency  of,  637. 
Generators,  efficiency  of,  637. 
Germ  theory  of  disease,  181. 
Grassy  odors,  167. 

Gravel,  flow  of  water  through,  99,  479. 
Ground-water,  89. 

collecting  works,  274. 

flow  of,  96,  101,  102. 

direct  measurement  of,  99. 


Ground-water,  methods  of  estimating  flow, 
94,  95,  99- 

form  of  surface,  90. 

formations  favorable  for,  91,  93. 

level  of,  90. 

occurrence,  89,  93. 

quantity  available,  102. 
Growth  of  cities,  34. 

Hard  waters,  effect  of,  on  soap,  151. 

relation  of,  to  disease,  150. 
Hardness  of  water,  151,  537. 
Heat-engines,  efficiency  of,  643. 
High  and  low  service,  769. 
High-water  alarm  for  stand-pipes,  etc.,  720. 
Household  filters,  532. 
Hydrants,  770. 

drainage  of,  770,  784. 

forms,  771. 

freezing,  772,  784. 

friction  in,  252,  770, 

location,  747. 

maintenance,  784. 

setting,  772. 

valves,  771. 
Hydraulic  dam  construction,  355. 

grade,  601,  602. 

ram,  662. 

transmission,  efficiency  of,  649. 

Ice,  action  of,  on  stand-pipes,  714. 
anchor,  269. 
bacteria  in,  168. 
pressure  on  dams,  387. 
Impounded  waters,  164. 
Impounding       reservoirs,    see       Reservoirs, 

storage. 
Impurities,     absorption     of,     by     meteoric 

waters,  153. 

Income  of  water  departments,  791. 
Incubation    at    blood-heat,    effect    of,    on 

bacterial  growth,  133. 
Indol  test  in  water  analysis,  136. 
Infection  of  well-waters,  175. 
Intakes,  259. 
lake,  266. 

anchor-ice  in,  269. 

Chicago,  271. 

construction,  268,  622,  623. 

cribs  for,  269. 

examples,  271,  622. 

location,  266. 

Milwaukee,  270,  622. 

sewage  pollution  at,  266. 

submerged  pipe,  268,  622,  623. 

tunnels,  268. 
river,  259. 

Cincinnati,  265. 

construction,  260. 

examples,  261,  263,  264. 

for  gravity  supplies,  266. 

location,  259. 

St.  Louis,  264. 

Steubenville,  263. 


INDEX. 


803 


Iron  in  waters,  150,  169. 

amount  necessary  to  impart  taste,  150. 

cause  of,  540. 

removal  of,  540. 

use  of  in  purification,  432,  543. 
bacterium,  170. 
Isochlors,  127. 

Joints  for  pipes,  cast-iron,  557. 
riveted,  567,  715. 
steel,  567,  569. 
wood,  575,  576. 

Kutter's  formula,  256. 

Lactose  agar  in  water  analysis,  135. 
Lakes,  intakes  for,  266. 

vertical  circulation  in,  163. 
Lead,  action  of  waters  on,  150,  572. 

pipe,  572. 

use  of  by  ancients,  2. 
Leakage  of  pipes,  21,  782. 
Liquefying  bacteria,  significance  of,  135. 
Lithium,    use    of,    in    detecting    pollution, 

120. 

Locking-bar  joint,  569. 
London,  water-supply  of,  8. 
Loss  on  ignition,  127. 

Low  temperatures,  influence  of,  on  typhoid, 
201. 

Maignen  "scrubber,"  530. 
Mains,  leakage  from,  21. 
Maintenance: 
conduits,  778. 
cost  of,  790. 

distributing  system,  782. 
pipe-lines,  779. 
pumping-stations,  780. 
reservoirs,  337. 
Malaria,  199. 
Manholes  in  pipes,  621. 

in  tanks,  721. 
Maps,  775. 

Masonry,  cost  of,  409,  624. 
weight  of,  381. 
aqueducts,  593. 
construction,  597. 
cost,  624. 
cross-sections,  594. 
Croton  596. 
details,  598. 
embankments  for,  597. 
gates,  599 
maintenance,  778. 
materials  for,  594. 
stability,  594. 
Wachusett,  596. 
dams,  see  Dams,  masonry, 
reservoirs,  702,  709. 
cost  of,  709,  710. 
covers  for,  705. 
Melosira,  167. 
Meteoric  waters,  153. 


Meter  rates,  792. 
Meters,  787. 

accuracy,  21,  788. 

cost,  789. 

durability,  788. 

requirements,  787. 

value  of,  in  waste  prevention,  24,  785. 
Microscopical  analysis  of  water,   120,    122, 

143- 

Molding  of  pipes,  562. 
Motors,  efficiency  of,  637. 
Mud,  bacteria  in,  166,  430. 
Multiplication  of  bacteria  in  water  samples, 

132. 

Nitrates,  significance  of,  130. 

Odors  in  water,  124,  167. 

due  to  algae,  167. 

fishy,  167. 

grassy,  167. 

Operation  of  water-works,  cost  of,  789. 
Organic  matter,  128. 
Orifices,  flow  through,  226. 
Overturning  of  lake-waters,  165. 
Oxygen  consumption,  129. 
Ozone  in  water  purification,  544. 

Parasitic  worms,  dangers  of,  143. 
Paris,  water-supply  of,  8,  9. 
Pasteur  filter,  532. 
Pathogenic  bacteria,  detection  of,  138. 

relation  of,  to  water  analysis,  135. 
Pediastrum,  168. 
Percolation,  54,  57. 

determined  by  stream-flow,  64. 
effect  of,  on  quality,  169. 
effect  of  vegetation  on,  61. 
experiments  on,  62,  64. 
relation  to  stream-flow,  54. 
Permanent  hardness,  151,  537. 
Peroxide    of    hydrogen    in    water    purifica- 
tion, 546. 

Physical  analysis  of  water,  120,  122. 
Physiological  bacterial  tests,  137. 
Pipe-lines,  586,  601. 

bridges  for,  618. 

calculations  of,  603. 

construction,  606. 

cost,  604,  624. 

covering,  610. 

crossings,  618. 

design  of,  601. 

details,  610. 

economical  size,  603. 

expansion-joints,  610. 

foundations,  607. 

freezing,  610. 

inspection,  609, 

manholes,  611. 

material  for,  601. 

pressures  in,  602. 

pressure-regulators,  606. 

profile,  60 1. 


804 


INDEX. 


Pipe-lines,  Rochester,  603. 
safety-valves,  617. 
terminals,  617. 
testing,  609. 
valves,  612. 
velocities  in,  606. 
molds,  562. 
moss,  1 80. 
scraper,  779. 

Pipes,  cast-iron,  see  Cast-iron  pipe, 
cement,  see  Cement  pipe, 
corrosion  of,  by  electrolysis,  782. 
depth  of  covering,  772. 
freezing,  610,  619. 
lead,  see  Lead  pipe, 
leakage  from,  21. 
location,  771. 
maintenance,  789. 
materials  for,  5-51. 
pressure  of  earth  filling,  553. 

water,  551,  602. 
protection  of  exposed,  619. 
scraping,  779. 
service,  see  Service-pipes, 
steel,  see  Steel  pipes, 
stresses  in,  551. 
thawing,  783. 
water-hammer  in,  552. 
wooden,  see  Wooden  pipe, 
wrought  iron,  565. 
Pitometer,  786. 
Platinum-cobalt  color  standard,  123. 

wire    method    of    determining    turbidity, 

123. 

Pneumatic  transmission,  549. 
Poisonous  metals  in  waters,  150. 
Pollution,     detection    of,     by    addition    of 

chemicals,  119. 
Population,  estimates  of,  34. 
Porosity  of  soils,  91. 
Potableness,  150. 
Potsdam  sandstone,  109,  112. 
Power  equivalents,  633,  634. 
pumps,  653,  659,  660,  661. 

efficiency  of,  674. 
Precipitation,  see  Rainfall. 
Pressure  in  distributing  system,  743. 
of  atmosphere,  224. 
of  water,  224. 
equivalents,  633. 
gauges,  value  of,  781. 
regulators,  616. 
relief-valves,  617. 
Prime  movers,  efficiency  of,  637. 
Protection  of  pipes  from  frost,  619,  756. 
Puddle,  347,  348. 
Pumping,  effect  of,  on  bacterial  content  of 

well-waters,  175. 
work  done  in,  631. 
machinery,  arrangement  of,  668,  677. 
calculation  of  efficiency,  670. 
capacity,  680. 
duty,  660,  662. 
economy  of  different  designs,  68 1. 


Pumping  machinery,  efficiency,  660, 662, 664, 
stations,  design  of,  677. 

operation  of,  780. 
Pumps,  air-chambers  for,  666. 
air-displacement,  660. 
air-lift,  662. 
Allis,  658. 

boiler  capacity  for,  681. 
bucket,  663. 

centrifugal,  316,  661,  670. 
classification,  649. 
Connersville  rotary,  659. 
continuous-flow,  660. 
deep-well,  660. 
details,  663. 
duplex,  654. 
efficiency,  672,  674. 
Gaskill,  657. 
Heisler,  656. 
hydraulic,  659. 
hydraulic  ram,  662. 
impeller,  660. 
impulse,  662. 
jet,  662. 
location  of>  668. 
power,  655,  659. 
reciprocating,  650. 
rotary,  659. 
slip  of,  1 6,  21. 
steam,  653. 

steam-displacement,  660. 
suction-pipes,  666. 
types  of,  651,  652. 
U  pump,  650. 
valves,  663. 
vacuum  chamber,  666. 
Worthington,  654,  655. 
Purification  of  streams,  157. 
causes,  158. 
effect  of  aeration,  163. 

competing  organisms,  162. 

dilution,  160. 

lack  of  food,  162. 

sedimentation,  160. 

sunlight,  161. 
of  water,  general  statement,  419. 

aeration,  see  Aeration. 

Anderson's  process,  543. 

chemical  processes,  544. 
chlorinated  lime,  545. 
peroxide  of  hydrogen,  546. 
ozone,  544. 

distillation,  543. 

electrolytic  methods,  542. 

filtration,  see  Filtration. 

for  domestic  purposes,  419. 

for  manufacturing  purposes,  419. 

imperfect,     Lausen     typhoid    outbreak 
due  to,  172. 

in  the  soil,  170. 

iron-removal,  540. 

methods,  420. 

number  of  plants,  422. 

objects  of,  419. 


INDEX. 


805 


Purification  of  water,  preliminary  treatment, 

494. 

sedimentation,  see  Sedimentation, 
softening,  536. 
sterilization,  543. 

Quality  of  water,  from  various  sources,  38. 

in  ancient  times,  8. 

relation  of,  to  character,  149. 

requirements,  150. 
Quantitative  bacterial  examination,  132. 

Rain-water,  bacterial  content  of,  153. 
Rainfall,  41. 

annual,  in  U.  S.,  43. 
maximum  rates,  49. 
measurement  of,  41. 
minimum,  47. 
monthly,  46. 
statistics,  43. 
variations  in,  43. 
Rain-gauges,  41. 
Rain-storms,  frequency,  50. 

maximum,  50,  51. 
Rates,  water,  792. 
Reinforced  concrete,  conduits  of,  597. 

reservoirs  of,  see  also  Filters. 
Reservoir  dams,  see  Dams, 
linings,  699. 

sediment,  bacteria  in,  430. 
Reservoirs,  ancient,  2. 

distributing,  see  Distributing  reservoirs, 
for  pipe-lines,  602,  617. 
storage,  327. 

capacity,  329,  331,  332. 
cleaning  of  site,  336. 
construction,  333. 
depth,  335. 
location,  333. 
maintenance,  337. 
organic  matter  in,  33. 
shallow  flowage,  337. 
surveys  for,  334. 
Revenue,  sources  of,  791. 
Rivers,  intakes  for,  259. 
Riveted  joints,  for  pipes,  567. 

for  stand-pipes,  715. 
pipes,  friction  in,  245,  246. 
Rocks,  porosity  of,  91,  109. 
Rope-gearing,  efficiency  of,  544. 
Rotary  pumps,  659. 
Run-off,  see  Flow  of  streams. 
Running  water,     physical     appearance     of, 
155- 

Safety-valves,  607. 

Salt,  use  of,  in  detecting  pollution,  120. 
Samples  for  analysis,  collection  of,  116. 
Sand,  analysis  of,  471. 

effective  size,  471. 

flow  of  water  in,  96. 

washing,  490. 
Sanitary  survey,  value  of,  144. 

water  analysis,  nature  of,  118. 


Saprol,  use  of,  in  detecting  pollution,  119. 
Scale,  boiler,  151. 
Scenedesmus,  168. 
Scrapers,  pipe,  779. 
Screens,  reservoir,  365. 
Sediment,  bacteria  in,  166,  430. 
in  streams,  155,  424. 
relation    to    bacterial    content    of    rivers, 

156. 
Sedimentation,  424. 

action  of  finely  divided  matter,  431. 
sulfate  of  alumina,  408. 
various  chemicals,  411. 
efficiency,  427,  428. 
limitations  of,  425. 
methods,  426. 
of    bacteria    in    purification    of    streams, 

1 60. 

plain,  426. 
theory  of,  426. 
time  required,  426,  436. 
coagulation,  431. 

action  of  chemicals,  432. 
amount  of  chemical  required,  434. 
efficiency,  437. 

preparation  of  coagulant,  444. 
rapid  sand  filtration,  506. 
slow  sand  filtration,  493. 
time  required,  436. 
Self-purification  of  rivers,  157, 
Separate     systems     of     supply,     213,    769, 

773- 

Service-connections,  772. 
Service-pipes,  friction  in,  244. 

maintenance,  782. 

materials  for,  582.  '. 

thawing,  721. 
Settling  basins,  438. 

Albany,  449,  465. 

Cincinnati,  448. 

clear-water  reservoir  for,  444. 

drain-pipes,  444. 

draw-off  arrangements,  441,  443. 

examples,  447. 

form  of,  440. 

inlet-  and  outlet-pipes,  414. 

methods  of  operation,  439. 

number,  439. 

Pittsburg,  448. 

St.  Joseph,  447. 

St.  Louis,  447. 

size,  439. 
Sewage     bacteria,     B.     cnteritidis    sporog., 

diagnosis  of,  135. 
physiological  character  of,  137. 

pollution,    value   of   certain    bacteria  in, 

J37' 
Sewer-gas,    relation    of,    to    typhoid    fever, 

185. 

Shafting,  efficiency  of,  644. 
Shoes  for  stave-pipe,  579. 
Sinking  fund,  217,  790. 
Sluice-gates,  366. 
Soft  water  vs.  hard  in  Glasgow,  151. 


8o6 


INDEX. 


Softening  of  water,  536. 

Archbutt-Deeley  process,  539. 
chemistry  of,  537. 
Clark  process,  538. 
Columbus,  O.,  513,  539. 
efficiency,  540. 
for  boiler  use,  540. 
Southampton,  Eng.,  539. 
Soil,  purification  of  water  in,  170. 
Soils,  porosity  of,  91. 
Solids,  total,  126. 

volatile,  127. 

Sources  of  water-supply,  38. 
Specials  for  cast-iron  pipe,  560. 
steel  pipe,  569. 
wooden  pipe,  579. 

Species,  significance  of  bacterial,  135. 
Springs,  102. 
artesian,  104. 
bacteria  in,  172. 
classification,  102. 
collecting  works  for,  274. 
yield  of,  105,  277. 
Stand-pipe  system,  209. 
Stand-pipes,  anchorage,  717. 
Stand-pipes,  automatic  valves  for,  720. 
bottom  details,  717. 
capacity,  690. 
details,  711.. 
dimensions,  711. 
encased,  721. 
foundations,  717. 
high-water  alarm,  720. 
ice-action  on,  714. 
inlet-pipes,  718. 
location,  711. 
maintenance,  781. 
manhole,  721. 
material  for,  714. 
ornamentation,  721* 
painting,  721. 
purpose  of,  689. 
reinforced  concrete,  735. 
riveting,  715. 
stresses,  713. 
thickness  of  plates,  715. 
valves,  719. 
wind-pressure,  713. 
Stave-pipe,  see  Wooden  pipe. 
Steam,    as    a    disinfectant    for    wells    and 

pipes,  141. 

boilers,  efficiency  of,  637. 
engine,  effect  of  condensers,  640. 

effect  of  operating  at  part  load,  642. 
efficiency,  639. 
expansive  use  of  steam,  639. 
steam-consumption,  641,  642. 
expansive  use  of,  639. 
Steel  for  pipes,  5660 

stand-pipes,  714. 
pipe,  565- 

advantages,  565. 
coating,  569. 
corrosion,  570. 


Steel  pipe,  cost,  626. 
details,  569. 

distortion  by  back-filling,  554. 
durability,  570. 
expansion-joints,  610. 
joints,  567,  569,  610. 
laying,  609. 
locking-bar  joint,  569. 
material  for,  566. 
riveting,  567. 
stiffening  of,  554. 
stresses,  551. 

temperature  stresses,  554,  568. 
thickness,  566. 
Sterilization,  543. 

Storage,  impairment  of  water  by,  177. 
improvement  of  water  by,  177. 
of  water,  327. 

reservoirs,  see  Reservoirs,  storage, 
tanks,  see  Tanks. 
Stored  waters,  164. 

diminution  of  dissolved  oxygen  in,  177. 
Storms,  great,  50. 
Streams,  flow  of,  see  Flow  of  streams. 

gauging  of,  258. 

Street-sprinkling,  water  used  for,  20. 
Submerged  pipes,  620. 
Suction-pipes,  304,  666. 
Sudbury  aqueduct,  coefficients  for,  258. 
Sulfate  of  alumina,  action  of,  432. 

amount  required,  434. 
Sulfate  of  lime,  solubility  of,  537. 
Sulfuric  acid,  use  as  disinfectant,  141. 
Sunlight,  effect  of,  on  bacteria,  161. 
Surface  waters,  154. 
appropriation  of,  328. 
as  portable  supplies,  154. 
Surveys,  sanitary,  144. 
Synedra,  167,  168. 
Syphon,  inverted,  620. 

ancient,  2. 

Systems  of  supply,  209,  213. 
separate  for  fire  service,  213. 

Tanks,  air-pressure,  735.        , 
elevated,  723. 

Ames,  Iowa,  728,  729. 

anchorage,  733. 

details,  733. 

dimensions,  723. 

economy  of,  723. 

inlet-pipe,  733. 

maintenance,  720. 

masonry  pedestal,  734. 

Murphysboro,  731,  732. 

reinforced  concrete,  735. 
.  stresses  in,  724. 

trestle  tower,  727. 

wooden,  734. 
pressure,  735. 
Tape-worms,  182. 
Taste  of  water,  124. 
Temperature  of  water,  124. 
stresses,  in  pipes,  554,  568. 


INDEX. 


SO/ 


Temporary  hardness,  152. 
Thawing  pipes,  783. 
Thermophone,  125. 
Tin-lined  pipes,  583. 
Tower,  see  Tanks,  elevated. 
Transmission  of  energy,  644. 
Trenching,  606,  773. 
Tuberculation,  564. 

effect  on  flow  of  water,  242. 
Tunnels,  as  conduits,  600. 
for  collecting  water,  320. 
Turbidity,  123. 

determination  of,  123,  124. 
Typhoid  bacillus,  in  feces,  184. 

methods  of  isolation,  in  water,  139. 
relation  of,  to  colon  bacillus,  140,  182. 
death-rates,    decline    in,    coincident    with 

improved  water-supplies,  190,  193. 
in  cities  on  Great  Lakes,  154. 
Munich,  194. 
river  cities,  154. 
Zurich,  194. 

index  of  quality  of  water-supplies,  191. 
fever,  caused  by  polluted  milk,  185. 
caused  by  polluted  wells,  189. 
filters  not  complete  protection,  458. 
method  of  introduction,  185. 
mortality  of,  186. 
period  of  incubation,  185. 
relation  of  sewers  to,  185. 
seasonal  distribution,  194. 
organism,  difficulties  in  detecting,  139. 
relation  to  colon  organism,  140,  182. 
vitality  of,  in  ice,  168. 

in  water,  200. 

outbreaks,  Chicago,  *9o-'92,  189. 
Havre,  France,  172. 
Lausen,  Switzerland,  172. 
Lowell-Lawrence,  Mass.,  'go-'gi,  188. 
Mohawk-Hudson  Valley,  '90-^91,  187. 
Plymouth,  Pa.,  191. 
Stamford,  Conn.,  185. 
Washington,  D.  C.,  190. 
Wittenberg,  Germany,  172, 

Units,  chemical,  125. 

hydraulic,  223. 
Uroglena,  167. 

Vacuum  chambers,  656. 
Valve-box,  613. 
Valves,  air,  614. 

automatic,  for  pipe-lines,  616. 
for  stand-pipes,  720. 

balanced,  482. 

blow-off,  615. 

filter-regulating,  481. 

location  of,  770. 

loss  of  head  in,  249. 

maintenance,  784. 

pump,  663. 

reservoir,  356,  399. 

stop,  612. 
Vapor  tension,  224. 


Venturi  meter,  248. 
Vitrified  pipe,  581. 
Volatile  solids,  127. 

Waste  prevention,  784. 
Waste-weirs,  capacity,  370. 

construction,  400. 

examples,  401. 

forms,  369,  400. 

importance  of,  344,  369. 
Water,  artesian,  176. 

consumption  of,  see  Consumption  of  water. 

flow  of,  see  Flow  of  water. 

flowing,  154. 

impounded,  164. 

measurement  of,  247. 

meteoric,  153. 

pressure  equivalents,  633. 

spring,  172. 

storage  of,  327. 

subterranean,  169. 

surface,  154. 

weight  of,  223,  632. 

well,  173. 
Water  analysis,  interpretation  of,  126. 

value  of  different  methods  in,  120. 
Water-borne  diseases,  183. 

relation  to  intestinal  canal,  183. 
Water-hammer,  252,  552. 
Water-power,  636. 

Water  purification,  see  Purification  of  water. 
Water-ram,  252,  552. 
Water-supplies,  ancient,  i. 

cost  of,  729. 

relation  of,  to  disease,  181. 

sources  of,  38. 
Water-table,  defined,  89. 

form  of,  90. 
Water-tower,   masonry,   722,  734;    see  also 

Tanks. 

Water-vapor,  pressure  of,  224. 
Water-weeds,  effect  of,  on  quality,  166. 
Water-works,  arrangement  of,  207,  208. 

classification,  207. 

depreciation,  216,  220. 

development  in  Europe,  9. 
in  U.  S.,  10. 

Roman,  2,  7. 

systems  of  operation,  209. 
comparison  of,  210. 
double  systems,  213,  773. 
Water-works    construction,    cost    compari- 
sons, 214. 
economy  of,  214. 
estimates  of  cost,  221. 
future  provision,  220. 
Water-works  management,  789. 
Waterphone,  786. 
Waves,  height  of,  352. 

pressure  of,  on  dams,  387. 
Weight  of  masonry,  379. 

of  water,  223. 

Weirs,  flow  of  water  over,  228. 
sharp-crested,  228. 


8o8 


INDEX. 


Weirs,  submerged,  231. 
various  sections,  231. 
Well,  Joseph's,  i. 
Well-points,  298. 
strainers,  300. 
Wells,  ancient,  i. 

artesian,  see  Artesian  wells, 
construction  of,  292,  310. 
disinfection  of,  141. 
driven,  see  Wells,  tubular, 
flow  of  water  into,  277. 

artesian,  283. 

calculation  of,  280,  288. 

effect  of  fissures,  292. 
size  of  well,  288. 

formulas  for,  278. 

high-pressure,  289. 

pipe-friction,  287. 
forms  of,  292. 
horizontal,  322. 
hydraulics  of,  277. 
large  open,  294. 

construction,  294. 

cost  of,  297. 

examples,  296. 

shoes  for  sinking,  295. 

yield,  296. 
large  vs.  small,  293. 
location,  292. 

of  pumps  in,  668. 
near  streams,  321. 
pumps  for,  668. 
push,  322. 
tubular,  297. 

air-chambers,  305. 

arrangement,  302. 

Brooklyn,  308. 

clogging  of,  306. 

connections,  304. 

Cook,  300. 

examples,  307. 

operation,  302. 


Wells,  tubular,  Plainfield,  307. 
sand-box,  305. 
sinking,  297. 
size,  304. 
spacing,  302. 
strainers,  300. 
suction  mains,  304. 
tests,  306. 
well-points,  298. 
yield,  303,  306. 
yield  of,  291. 
decrease  in,  291. 
estimates  of,  288. 
Wire-rope  transmission,  644. 
Work  and  power  equivalents,  633,  634^ 
Wood-stave  pipe,  friction  in,  247. 
Wooden  pipe,  575. 
advantages,  575. 
bored  pipe,  575. 
construction,  609. 
early  use  of,  10. 
stave-pipe,  576. 

bands  for,  576,  577. 
size,  577. 
spacing,  578. 
construction,  609. 
coupling-shoes,  579. 
cost,  626. 
durability,  580. 
leakage,  580. 
specials,  579. 
staves,  576. 
Wyckoff  pipe,  575. 
Wooden  tanks,  735. 
maintenance,  781. 
Worms,  parasitic,  182. 
Wrought-iron  pipe,  565. 
Wyckoff  pipe,  575. 

Zinc  in  water,  150,  583. 
Zones  of  pressure,  769. 


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